Abstract Book Phosphorous Conference

8/12/2019 Abstract Book Phosphorous Conference

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Dirk PoelmanPhilippe Smet

Joke Hadermann

Jonas BottermanKoen Van den Eeckhout


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Persistent luminescence can perfectly beexplained to the layman. Everyone knows theglow-in-the-dark stars and the tiny glowingghosts from several toy companies. The

phenomenon is also associated with glowingmarkers on wrist watches and night-glowpushbuttons. However, it is very oftenconfused with radioactive materials, and mostpeople have no clue how and why thesematerials are glowing, nor what kinds ofmaterials are suitable. Unfortunately, thissomewhat relates the layman to us,researchers in the field. Just like the layman, westill dont really know how and why brightpersistent luminescence can be obtained:several models, based on theoreticalconsiderations, numerical simulations andextensive experimenting have been proposed,but there are no final answers yet. On theexperimental side, new and very performingmaterials have been developed, but mostprobably, these are still far from optimum. Inaddition, there are probably countless othermaterials both hosts and dopants which areappropriate.,

Our research group LumiLab at GhentUniversity has been working on luminescentmaterials for many years, and it is only since afew years that we started working on persistentluminescence. It was to our surprise that,despite the wealth of possible application,there appeared to be only a relatively smallresearch community working on persistentphosphors, and that there were no workshopsor conferences devoted to the topic.

About a year ago triggered by writing an EU-COST proposal and a review paper onpersistent luminescence we developed the

plan to organize a small-scale meeting focusingon persistent and storage phosphors. Thiswould enable a melting pot of ideas pouringall existing expertise and models together andstrengthen the bonds between researchers inthe field.

We hope that, thanks to your contributions, thefirst Phosphoros meeting will achieve thisgoal. We trust that you will have theopportunity to discuss new ideas andexperiments. Also, we would be very glad if

Phosphoros at UGent is not the last meeting onthis exciting topic.

Finally, we want to thank everybody who hascontributed to Phosphoros: the members ofthe program committee, our invited speakers,the contributors of oral and posterpresentations, our co-organizers Koen Van denEeckhout, Jonas Botterman and Joke

Hadermann, the entire LumiLab research groupand, last but not least, our sponsors AgfaGevaert, Sysmex, FWO-Flanders and GhentUniversity.

May the light be with you!

Dirk Poelman and Philippe Smet,Conference chairs


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Committees 6

Program 7

Abstracts: Invited lectures 11

Abstracts: Oral presentations 18

Session I: Eu 2+-doped persistent phosphors 18

Session II: Applications of persistent phosphors / Energy storage 31

Session III: Thermoluminescence / Persistent luminescence models 42

Session IV: Non Eu 2+-doped persistent phosphors 55

Abstracts: Poster presentations 64

List of abstracts 95

List of contributing authors 99


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Local organizing committee

Dirk Poelman

Philippe SmetJoke HadermannJonas BottermanKoen Van den Eeckhout

International advisory committee

Marco Bettinelli University of Verona Italy

Philippe Boutinaud University of Clermont-Ferrand FrancePieter Dorenbos Delft University of Technology The NetherlandsJorma Hls University of Turku FinlandDariusz Hreniak Inst. of Low Temperature and Structure Research PolandStphane Jobic Universit de Nantes FranceThomas Jstel University of Applied Sciences Mnster GermanyAndries Meijerink Utrecht University The NetherlandsDirk Poelman Ghent University BelgiumPhilippe Smet Ghent University Belgium

Wieslaw Strek Inst. of Low Temperature and Structure Research PolandBruno Viana Laboratoire de Chimie de la Matire Condense FranceXiaojun Wang Georgia Southern University United StatesEugeniusz Zych University of Wroclaw Poland


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00 Introduction

Session I: Eu2+

-doped persistent phosphors

15 Persistent luminescence mechanisms: Human imagination at work Jorma Hls, University of Turku, Finland

00 Synthesis and characterization of BaAl 2O4:Eu2+

co-doped with different rare earth ionsMartin Ntwaeaborwa, University of the Free State, South Africa

20 DFT and synchrotron radiation study of the Eu2+

doped BaAl 2O4 Taneli Laamanen, University of Turku, Finland

Coffee break

10 Surface characterization and luminescent propertiesof SrAl2O4:Eu

2+,Dy3+ nano thin filmsHendrik C. Swart, University of the Free State, South Africa

30 Fabrication of long-lasting glass-ceramic phosphorsby melt-quenching method and their propertiesSetsuhisa Tanabe, Kyoto University, Japan

50 Luminescence studies of a combustion-synthesizedblue-green BaAl xOy:Eu

2+,Dy3+ nanophosphorsFrancis B. Dejene, University of the Free State, South Africa

10 Synthesis, persistent luminescence, and thermoluminescence

properties of yellow Sr 3SiO5:Eu2+,RE3+ (RE = Ce,Nd,Dy,Ho,Er,Tm,Yb)and orange Sr 3-xBaxSiO5:Eu

2+,Dy3+ phosphor Jing Wang, Sun Yat-sen University, China

30 Yellow persistent luminescence in Sr 2SiO4:Eu2+,Dy3+

Thomas Jstel, Fachhochschule Mnster, Germany

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Session III: Thermoluminescence / Persistent luminescence models

15 Thermoluminescence as a tool to studythe mechanism of persistent luminescence

Adrie J.J. Bos, Delft University of Technology, The Netherlands

00 Thermoluminescence study of persistent luminescence fadingin Sr2MgSi2O7:Eu

2+,R3+ materialsMika Lastusaari, University of Turku, Finland

20 Thermally stimulated luminescence:an algorithm for analysing phosphorescence curvesEduardo Caselli, Universidad Nacional del Centro, Argentina

Coffee break

10 Charging behaviour in persistent phosphorsKoen Van den Eeckhout, Ghent University, Belgium

30 Photoionization of lanthanide defects and how that affectsluminescence and carrier storagePieter Dorenbos, Delft University of Technology, The Netherlands

50 Controlling trap depth to enhance persistent luminescenceof silicate nanoparticles for in vivo imagingThomas Maldiney, UPCGI Paris, France

10 An x-ray absorption study of SrAl 2O4:Eu,Dy powdersKatleen Korthout, Ghent University, Belgium

30 ZnGa 2O4:Cr3+: a new red long-lasting phosphor with high brightness Aurlie Bessire, LCMCP Paris, France

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Session IV: Non-Eu 2+-doped and infrared-emitting phosphors

50 Persistent phosphorescence through persistent energy transfer Xiaojun Wang, Georgia Southern University, USA

35 IR laser stimulated afterglow fluorescence ofEu(III) doped LaAlO3 nanocrystalsPawe Guchowski, Institute of low temperature

and structure research Wrocaw, Polan d

55 Synthesis and characterization of Y 2O2S:Eu nanophosphorsusing sol-combustion method

Abdub Ali, University of the Free State, South Africa

Coffee break

40 Persistent phosphorescence in Ce 3+-doped Lu 2SiO5 Mitsuo Yamaga, Gifu University, Japan

00 Long-lasting phosphorescence of Ce 3+-doped garnet crystals Jumpei Ueda, Kyoto University, Japan

20 Synthesis and characterization of calcium titanium oxide basedpigments with red afterglowEugenio Otal, EMPA, Switzerland

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I 01 Persistent luminescence mechanisms: Human imagination at work 12 Jorma Hls, University of Turku, Finland

I 02 Storage and read-out mechanisms in the best photostimulable 14phosphor materials for digital radiography: BaFBr:Eu and CsBr:Eu Miroslaw Batentschuk, University of Erlangen-Nrnberg, Germany

I 03 Thermoluminescence as a tool to study the mechanism 15of persistent luminescence

Adrie J.J. Bos, Delft University of Technology, The Netherlands

I 04 Persistent phosphorescence through persistent energy transfer 17 Xiaojun Wang, Georgia Southern University, USA


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Persistent luminescence mechanisms: Human imagination at work I 01

Hermi F. Brito 1, Jorma Hls 1-3,*, Taneli Laamanen 2,4, Mika Lastusaari 2,3, Marja Malkamki 2,4,Lucas C.V. Rodrigues 1,2

*Corresponding author: [email protected] de So Paulo, Instituto de Qumica, Departamento de Qumica Fundamental, So Paulo, Brazil2University of Turku, Dep artment of Chemistry, FI20014 Turku, Finland 3Turku University Centre for Materials and Surfaces (MatSurf), Turku, Finland4Graduate School of Materials Research (GSMR), Turku, Finland

Keywords : persistent luminescence, mechanisms, europium, terbium

The persistent luminescence will pass its 400 th anniversary in 2012 though this importantmilestone is somewhat uncertain [1]. During its entire lifetime, the origin of persistentluminescence has certainly stimulated the mental activity of both scientists and laymen alike butno significant progress in the explanation of the phenomenon was made prior to the 21 st century.

In fact, in the early times ( i.e. the 17 th century), revolutionary ideas were not particularly greetedwith official recognition ( cf. Galileo Galilei spent his life under house arrest since 1632) and thustaking initiative to explain controversial phenomena may have been dangerous.

The lack of knowledge about the origin of the phenomenon was not, however, preventing thecommercial use of such materials ( e.g. copper doped ZnS [2]). The poor performance of ZnS:Cupaved way to true innovations, e.g. to increase the excitation strength, the only radioactive (andartificial) rare earth, promethium (Pm 3+) was used until the effects of radioactivity were realized.Only the advent of the new Eu 2+ based materials ( e.g. aluminates MAl 2O4:Eu

2+,R3+) [3] kicked off a

serious boom in their study first to discover and then to elucidate the mechanism. In the 1990s,it was thought that sufficient knowledge had been accumulated on the (luminescence) propertiesof both the di- and tri- or even the tetravalent rare earths. The harsh reality was soon to prove theopposite, however, and the details of the persistent luminescence are still under debate.

In one of the first rather schematic mechanisms (Fig. 1), it was suggested quite uncommonspecies, e.g. Eu+ [3]. Of course, under ambient conditions such cannot be found as the simplechemistry would suggest. In the following years, alternative species as R 2+ and R IV (R4+) wereintroduced as well, though these mechanisms relied on the existence of the Eu 2+-R3+ and Eu 3+-R2+ (or similar) redox pairs. Unfortunately, it is now clear that persistent luminescence from Eu 2+ canbe observed without R3+ co-doping [4] though such co-doping frequently enhances evendrastically the original persistent luminescence [5]. Both electron and hole trapping mechanismswere suggested for Eu 2+ based materials. This proliferation evidently resulted from the lack ofeven the basic information of the energetics of the system ( i.e. the host band gap and the positionof the Eu 2+/R2+/R3+/defect level positions therein). In some cases, if these positions were notknown, they were invented leading to some wild (and false) guesses The ignorance about thelevel positions was removed by the invaluable work of P. Dorenbos [6] and thus the door tomaster the excitation, emission as well as electron and hole trapping mechanisms was now open.However, the question on the nature of defects capable of storing the excitation energy, remains.

The persistent luminescence has now been extended from the complete dominance of efficientEu2+ based materials to the Eu 3+ [7] and Tb 3+ [8] based materials as well. Although the
mailto:[email protected]:[email protected]


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mechanisms for these ions are basically an open question, there exist models to predict them.Despite the persistent luminescence of Ce 3+ and Tb 3+ should follow the well-beaten track of Eu 2+ (electron trapping), the mechanism (Fig. 2) for Eu 3+ may be explained by hole trapping [7].Following the drastic increase in the price of the rare earth oxides (from 2010 to 2011: up to tenfold increase!), interest has emerged to use non-rare earth materials ( e.g. with Ti 3+ doping).

The experimental work based on trial and error, may be replaced in the future by computationalmethods. Considerable progress has been achieved in the reliable and realistic calculation of thehost band gap as well as energy level positions [9]. It might, however, be difficult if not impossible,to calculate the defect energy levels because of the minute amounts of thermal energy involved.

In conclusion, the importance of imagination and creativity in the explanation of new

luminescence phenomena should not be underestimated at the early stages, at least. However,the basics of chemistry, physics, spectroscopy and materials science should not be forgotten,either, since only the successful use of interdisciplinary competence leads to successfulinnovations. As the story of persistent luminescence has, hopefully, shown

[1] E. Newton Harvey, A History of Luminescence: From the Earliest Times until 1900 , Amer. Phil. Soc.,Philadelphia, PA, USA (1957) 307.

[2] S. Shionoya et al. , Phosphor Handbook , CRC Press, Boca Raton, FL, USA (2007) Ch12.3.[3] T. Matsuzawa et al. , J. Electrochem. Soc. 143 (1996) 2670.

[4] P.F. Smet et al. , 16th

Int. Conf. Lumin. (ICL'11) , June 27-July 1, 2011, Ann Arbor, MI, USA.[5] H.F. Brito et al. , J. Therm. Anal. Calorim. 105 (2011) 657.[6] P. Dorenbos, Phys. Stat. Sol. b 242 (2005) R7 (and many more recent works).[7] J. Hls et al. , 16 th Int. Conf. Lumin. (ICL'11) , June 27-July 1, 2011, Ann Arbor, MI, USA.[8] L.C.V. Rodrigues et al. , 16 th Int. Conf. Lumin. (ICL'11) , June 27-July 1, 2011, Ann Arbor, MI, USA.[9] T. Laamanen et al. , 16 th Int. Conf. Lumin. (ICL'11) , June 27-July 1, 2011, Ann Arbor, MI, USA.

Figure 1 : Persistent luminescence mechanism forSrAl2O4:Eu

2+,Dy3+ [3]. Note the false Eu + species!Figure 2: Persistent luminescence mechanism

for Eu 3+ in Y2O2S [7].

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Eu2+ 8S7/2

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[Eu3+]* [Eu3+-e -]* or [Eu2+]*

Y2O

2S:Eu 3+,Ti3+

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E [ E u

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kT


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Storage and read-out mechanisms in the best photostimulable I 02phosphor materials for digital radiography: BaFBr:Eu and CsBr:Eu

Miroslaw Batentschuk*, Peter Hackenschmied, Andres Osvet, Albrecht Winnacker

*Corresponding author: [email protected] of Erlangen-Nrnberg, Germany

Keywords : storage phosphors, BaFBr:Eu, CsBr:Eu, F-center, energy transfer

Since the introduction of X-ray imaging systems based on image plates [1], BaFBr doped with Eu 2+ and related storage phosphors, such as for instance BaSrFBr:Eu [2,3,4] have shown superiorproperties among a large number of photostimulable materials. In the last years, the needle imageplates (NIPs) based on CsBr:Eu 2+ storage phosphor are increasingly used for digital X-ray imaging.These NIPs offer better image quality and allow exposure dose reduction of up to 75 % comparedto the dose required when granular BaFBr:Eu image plates are used.

The operation of the both types of image plates relies on the occurrence of X-ray inducedphotostimulated luminescence (PSL). After irradiation, the charge carriers can be stored in traps,formed by crystal defects. For both materials referred here, the electron trap is F- center, and thehole trap is v k-center (or H-center) stabilised by a neighboring Eu

2+ ion [5,6]. However, the creationof new F-H-pairs during the irradiation is more pronounced in CsBr:Eu [7] than in BaFBr:Eu [8]. Adetailed analysis of the storage center creation for CsBr:Eu and BaFBr:Eu can be found in [7] and[9] respectively.

The read-out process is essentially absorption of light in F-centers. It is important that the excited

state of the F-center relaxes after excitation. As a result, a state is built slightly lower thanconduction band which allows a thermal excitation into the conduction band and migration of theelectron to the hole. The next, very interesting process for physics of storage phosphors is theenergy transfer from the electron-hole recombination to the Eu 2+ emitting centers [7] [10].

[1] M. Sonada et al. , Radiology 148 (1983) 833-837.[2] R.J. Klee, J. Phys. D: Appl. Phys. 28 (1995) 2529-2533[3] A. Meijerink, Mat. Chem. Phys. 44 (1996) 170-177.[4] M. Batentschuk et al. , Radiat. Meas. 29 (1998) 299-305.

[5] M. Thoms et al. , Phys. Rev. B 44 (1991) 9240-9247.[6] P. Hackenschmied et al. , Nucl. Instr. Methods Phys. Res. B 191 (2002) 163-167.[7] M. Weidner et al. , J. Appl. Phys. 106 (2009) 063514.[8] H. H. Rter et al. , Phys. Rev. Lett. 65 (1990) 2438-2442.[9] S. Hesse et al. , J. Appl. Phys. 105 (2009) 063505.[10] P. Hackenschmied et al. , Radiat. Meas. 33 (2001) 669-674.


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Thermoluminescence as a tool to study the mechanism I 03of persistent luminescence

Adrie J.J. Bos*, Pieter Dorenbos

*Corresponding author: [email protected] Materials Research Group, Delft University of Technology, Delft, The Netherlands

Keywords : thermoluminescence, persistent luminescence mechanism, trap depth, TL excitation

Persistent luminescence is the phenomenon that luminescence can last for hours after thetermination of the excitation. At least two kinds of active centres are involved: a luminescencecentre and a trapping centre. The luminescence centre can be studied by emission spectroscopyand the trapping centre by thermoluminescence. Thermoluminescence (TL) is the thermallystimulated emission of light of the phosphor following the previous absorption of energy ofradiation. TL is usually observed by measuring the luminescence while the sample is heated at a

constant heating rate. The curve obtained in this way is called a glow curve. In this contributionwe will review how glow curves measured under different circumstances can help us to get insighthow the trapping centres are involved in the mechanism of the persistent luminescence.

In Fig. 1 the glow curves of a well-known persistent luminescence phosphor, SrAl 2O4:Eu2+,Dy3+, are

shown after excitation with light of different wavelengths. It can be seen that the glow curveshows a broad, asymmetrical glow peak. Such glow peaks are characteristics for most persistentluminescent phosphors. Studying the shape and location of the peak can provide insight into thetrap depth or distribution of trap depths responsible of the glow peak. However, the derivation of

these trap depth values is not straightforward. It depends on the model that is used to describethe TL mechanism. Is there a single trap depth? Is retrapping of the charge possible? To derivesolid information it is necessary to perform a series of experiments. A first series involve themeasurement of TL glow curves with different waiting times between excitation and readout toinvestigate whether the decay of the TL glow peak corresponds with the decay of the persistentluminescence. A second series involve the measurement of TL glow curves as function of the

Figure 1 : Glow curves of SrAl 2O4:Eu2+,Dy3+ excited by photons of different wavelengths.

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period of excitation to see whether the glow peak maximum shifts to lower temperature withexcitation duration. If so this might be an indication for second order kinetics. Another seriesinvolve the measurement of TL glow curves as function of the heating rate. From the shift of theglow peak maximum the trap depth can be derived. Finally the measured glow curves can besubmitted to glow curve analysis. Only if different methods yield the same trap depth one cantrust the outcome.

From TL glow curves also information can be obtained about the source of the charge carriersliberated during exposure and about the position of the energy levels. The idea is the following:monochromatic light is used to excite electrons from impurity states within the band gap into theconduction band. The thus created free electrons will be captured in available trapping centres ofthe sample. The traps are subsequently read out by heating the sample while thethermoluminescence is recorded. By varying the wavelength, repeating the TL readout, anddisplaying the temperature integrated TL yield as function of the wavelengths the TL excitationspectrum (TLES) will be obtained [1]. In Fig. 2 an example is of such a spectrum is shown together

with the 10 K photoluminescence excitation spectrum (PLES) of Eu2+

emission. The PL excitationspectrum of the Eu 2+ 5d 4 f emission starts at around 475 nm, rises steeply to the maximumaround 425 nm, and falls off for lower wavelengths before showing a second maximum at 363 nm.The TLES starts at the same wavelength but shows a gradual increase in intensity with shorterwavelengths until a maximum is reached. It is clear that there are differences between the TL andPL spectra but most important is the observation that the onset of the PL excitation spectrumcoincides with the onset of the TL excitation spectrum. This observation is a strong indication thatexcitation of Eu 2+ leads to trap filling, which is the first step in the persistent luminescencemechanism.

Figure 2: Excitation spectra of SrAl 2O4:Eu2+,Dy3+. Thermoluminescence excitation

spectrum (TLES) is obtained by integration of the TL glow (see Fig. 1) between 300and 400 K. Photoluminescence excitation spectrum (PLES) is obtained by

measuring the Eu 2+ 5d 4f emission at 10 K.

[1] A.J.J. Bos et al. , J. Lumin. 131 (2011) 1465-1471.

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Persistent phosphorescence through persistent energy transfer I 04

Xiaojun Wang 1,*, Jiahuan Zhang 2

*Corresponding author: [email protected] Department of Physics, Georgia Southern University, Statesboro, USA2 Key Laboratory of Excited State Processes, CIOMP, CAS, Changchun, China

Keywords : persistent energy transfer, phosphors, phosphorescence

Persistent phosphorescence requires the traps for storing the excitation energy that can be slowlyreleased. The nature of the traps and their mechanisms for capturing energy are complicated andnot totally understood yet, making it difficult to synthesize the persistent phosphors withdesignated coloration and/or persistent time. Energy transfer processes in doped insulationmaterials, however, are well understood in terms of multipolar interactions between the donor orsensitizer and acceptors or emitter. If the donor has a high-frequency, efficient persistentemission, the excitation may persistently transfer to the acceptor, yielding the persistent emissionin the desired wavelength with similar persistent time to that of the donor [1-6]. The process canalso be used to enhance some inefficient phosphorescence and to prepare a single-phase full-colorphosphor material [7].

In this presentation, rare earth and transition metal ions doped aluminates, silicates, germinates,and titanates samples have been prepared and their optical properties and dynamical processesinvestigated. Long persistence phosphorescence has been obtained in different visible andinfrared regions using the mechanism of persistent energy transfer. Both visible and infraredphosphorescence lasts for more than 10 hours viewed directly by the eyes for visible or through

the G3 detectors for infrared emissions. Optical excitation, emission, thermoluminescence,photoconductivity, and photo-ionization with resonant microwave absorption have beenemployed in studying the mechanism. Most recent developments in persistent energy transferresearch have been discussed.

[1] D. Jia et al. , Appl. Phys. Lett. 80 (2002) 1535-1537.[2] X.J. Wang et al. , J. Lumin. 102 (2003) 34-37.[3] R.X. Zhong et al. , Appl. Phys. Lett. 88 (2006) 201916.[4] S.Ye et al. , J. Appl. Phys . 122 (2007) 063545-1-6.[5] D. Jia et al. , Electrochem. Solid-State Lett. 13 (2010) J32-J34.[6] Y. Teng et al. , J. Electrochem. Soc. 158 (2011) K17-K19.[7] J.S. Kim et al. , Appl. Phys. Lett. 84 (2004) 2931-2933.


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Session I: Eu 2+-doped persistent phosphors

O 01 Synthesis and characterization of BaAl 2O4:Eu2+ 19co-doped with different rare earth ionsMartin Ntwaeaborwa, University of the Free State, South Africa

O 02 DFT and synchrotron radiation study of the Eu 2+ doped BaAl 2O4 21 Taneli Laamanen, University of Turku, Finland

O 03 Surface characterization and luminescent properties 23of SrAl2O4:Eu

2+,Dy3+ nano thin filmsHendrik C. Swart, University of the Free State, South Africa

O 04 Fabrication of long-lasting glass-ceramic phosphors 25by melt-quenching method and their propertiesSetsuhisa Tanabe, Kyoto University, Japan

O 05 Luminescence studies of a combustion-synthesized 26blue-green BaAl xOy:Eu

2+,Dy3+ nanophosphorsFrancis B. Dejene, University of the Free State, South Africa

O 06 Synthesis, persistent luminescence, and thermoluminescence 28properties of yellow Sr 3SiO5:Eu2+,RE3+ (RE = Ce,Nd,Dy,Ho,Er,Tm,Yb)and orange Sr 3-xBaxSiO5:Eu

2+,Dy3+ phosphor Jing Wang, Sun Yat-sen University, China

O 07 Yellow persistent luminescence in Sr 2SiO4:Eu2+,Dy3+ 30Thomas Jstel, Fachhochschule Mnster, Germany


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Synthesis and characterization of BaAl 2O4:Eu2+ O 01

co-doped with different rare earth ions

Mantwa A. Lephoto 1, Shreyas Pitale 1, Bakang M. Mothudi 1,2, Hendrik C. Swart 1, Martin O.Ntwaeaborwa 1,*

*Corresponding author: [email protected] of Physics, University of the Free State, Bloemfontein, South Africa2Department of Physics, University of South Africa, Pretoria, South Africa

Keywords : combustion method, initiating temperature, photoluminescence, thermoluminescence

Barium aluminate (BaAl 2O4) belongs to a class of materials reperesented by a general formulaMAl2O4 (M= Ba

2+, Sr2+, Ca2+, or Mg 2+). These materials are widely used as host for Eu 2+ and RE3+ (RE= rare-earths) to prepare long afterglow (persistent luminescence) phosphors for a variety ofapplications in lighting. In this study, blue emitting BaAl 2O4:Eu

2+,RE3+ (RE = Dy3+, Nd3+, Gd 3+, Sm 3+,

Ce3+, Er3+, Pr3+ and Tb 3+) phosphors were prepared by a combustion method using initiatingtemperature of 600 oC and urea as a fuel. Photoluminescent (PL) and long afterglow properties ofthe blue emitting BaAl 2O4:Eu

2+,RE3+ phosphors were investigated for possible application inluminous paints, emergency vehicle lighting, field emission display technology, sensing anddosimetry.

Figure 1 shows PL emission spectra of BaAl 2O4:Eu2+:RE3+ (RE = Dy3+, Nd3+, Gd3+, Sm3+, Ce3+, Er3+, Pr3+

and Tb 3+) recorded when the phosphors were excited with a 325 nm HeCd laser in air at roomtemperature. All the samples exhibit a broad band bluish-green emission with a maximum at 500

nm. This bluish-green emission is ascribed to the 4f 6

5d1

4f 7

transitions of Eu2+

. The highest PLintensity was observed from the BaAl 2O4:Eu

2+ sample co-doped with Er 3+ and the least intensitywas observed from the Ce 3+ co-doped sample. Note that only the samples co-doped with Nd 3+ andDy3+ exhibited relatively long persistent luminescence compared to other samples.

Figure 1: PL emission spectra of BaAl 2O4:Eu2+

,RE3+

(RE = Dy3+, Nd3+, Gd3+, Ce3+, Er3+) phosphors.


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Figure 2 shows the (a) decay curves of BaAl 2O4:Eu2+,RE3+ (RE = Dy3+, Nd 3+, Gd3+, Ce3+, Er3+) and (b)

thermoluminescence spectrum of BaAl 2O4:Eu2+,Nd3+. The longer afterglow was observed from the

BaAl2O4:Eu2+ sample co-doped with Nd 3+. The traps responsible for the long afterglow are

presented in the thermoluminescent glow curve of BaAl 2O4:Eu2+,Nd3+ in figure 2 (b).

Figure 2: (a) Decay curves of BaAl 2O4:Eu2+,RE3+ (RE = Dy3+, Nd3+, Gd3+, Ce3+, Er3+)

and (b) thermoluminescence spectrum of BaAl 2O4:Eu2+,Nd3+.

It is well known that the long afterglow is due to trapping and detrapping of charge carriers.Possible mechanism of the long afterglow of BaAl 2O4:Eu

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DFT and synchrotron radiation study of the Eu 2+ doped BaAl 2O4 O 02

Hermi F. Brito 1, Maria C.F.C. Felinto 2, Jorma Hls 1,3,4 , Taneli Laamanen 3,5,*, Mika Lastusaari 3,4,Marja Malkamki 3,5, Pavel Novk 6, Lucas C.V. Rodrigues 1,3, Roberval Stefani 1

*Corresponding author: [email protected] de So Paulo, Instituto de Qumica, Departamento de Qumica Fundamental, So Paulo, Brazil2Instituto de Pesquisas Energticas e Nucleares, Centro de Qumica e Meio Ambiente, So Paulo, Brazil3University of Turku, Department of Chemistry, Turku, Finland4Turku University Centre for Materials and Surfaces (MatSurf), Turku, Finland5Graduate School of Materials Research (GSMR), Turku, Finland6 Academy of Sciences of the Czech Republic, Institute of Physics, Prague, Czech Republic

Keywords : DFT calculations, electronic structure, persistent luminescence, barium aluminate

Persistent luminescence materials release stored energy as light gradually at room temperature.The alkaline earth aluminates doped with Eu 2+ and R 3+ (MAl2O4:Eu

2+,R3+; M: Ca/Sr/Ba; R: e.g.

Nd/Dy [1]) are among the most efficient ones. The development of even more efficient materialsis hindered by the lack of knowledge on the effect of charge compensation defects and structuraldistortions resulting from the charge/size mismatch between the R 3+ and M 2+ ions. The defectsmay play either a desired or unwanted role as energy storage or luminescence quenching centers,respectively. Neither it is clear the exact electronic structure (band gap, valence (VB) andconduction band (CB) composition, Eu 2+/R3+ 4f 7 and 4f 65d 1 level positions) of MAl 2O4:Eu

2+,R3+.

In this work, the ab initio density functional theory (DFT) calculations using the WIEN2k programpackage [2] were employed together with experimental methods to study the Eu 2+ doped BaAl 2O4.Every eighth of the hosts Ba2+ ions was replaced with Eu 2+ and the different energy schemes werecalculated. Selected luminescence properties were studied experimentally by using thesynchrotron radiation (SR) VUV-UV-vis spectroscopy.

The BaAl2O4 structure was found less distorted with Eu2+ substituting Ba1 than Ba2 as witnessed

by the three-fold average decrease in the Eu-O distances for the latter. In addition, the difference(40 eV) in the total energies suggests that Eu 2+ prefers the Ba1 site which may result in only oneemission band, at least at low ( e.g. 1 mole-%) doping levels. The VB is mainly of the O 2pcharacter, whilst the CB consists mostly of the Ba (5.3 to 13 eV) and Al (13+ eV) levels.

Figure 1: Calculated (GGA+U method) bandstructure of MAl 2O4:Eu

2+ (M: Ca/Sr/Ba).

-5 0 5 10 150

50

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Only fair agreement was found between the calculated (5.7) and experimental (6.5 eV) band gapenergy. This may be due to the covalent character in BaAl 2O4. The increasing lattice covalency inthe MAl 2O4 (Ca Sr Ba) series moves the Eu

2+ 4f 7 ground level towards VB (Figure 1). After theoptimization of the crystal structure, the 4f 65d 1-4f 7 energy difference was 4.3 eV for both Ba sites.This suggests that the emission energy is the same irrespective of the Ba site occupied by Eu 2+.

The experimental band gap energy decreased slightly (with 0.1 eV from 10 to 300 K) withincreasing temperature. This is in agreement with the conventional behaviour found for thesemiconducting materials [3]. The SR emission spectrum consists of two bands (2.4 and 2.8 eV)which may be due to the 4f 65d 1 4f 7 emission of Eu 2+ in both Ba sites (Figure 2). However, this isnot directly indicated by the electronic structure calculations (see above). The weak additionalluminescence band may thus also originate from the possible creation of a new Ba 2+ site due tothe effect of water exposure on BaAl 2O4:Eu

2+ [4].

Figure 2: The synchrotron radiationexcited ( exc: 92 nm) emission spectraof BaAl2O4:Eu

2+,Dy3+ at selectedtemperatures between 10 and 300 K(SUPERLUMI, HASYLAB).

The DFT results show that the calculations are an excellent tool to probe the crystal and electronicstructure of the Eu 2+ doped persistent luminescence materials especially when difficult orimpossible to study experimentally. Trap states induced by the isolated defects and defectaggregates present in the BaAl 2O4:Eu

2+,R3+ materials should still be studied in detail since they areexpected to have a crucial effect on the persistent luminescence efficiency of these materials.

Acknowledgments: Financial support is acknowledged from the Turku University Foundation, Jenny andAntti Wihuri Foundation (Finland) and the Academy of Finland (contracts #123976/2006, #134459/2009

and #137333/2010). The DFT calculations were carried out using the supercomputing resources of the CSCIT Center for Science (Espoo, Finland).

[1] T. Matsuzawa et al. , J. Electrochem. Soc. 143 (1996) 2670-2673.[2] P. Blaha et al. , In: Schwarz, K. (Ed.), WIEN2k, An Augmented Plane Wave + Local Orbitals Program for

Calculating Crystal Properties, Users Guide , Vienna University of Technology, Austria, 2001.[3] Y.P. Varshni, Physica 34 (1967) 149-154.[4] H.F. Brito et al. , Academy of Finland Seminar: Materials in Photonics , Helsinki, February 15, 2011

(Poster).

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Surface characterization and luminescent properties of O 03SrAl2O4:Eu

3+,Dy3+ nano thin films

Hendrik C. Swart, Martin O. Ntwaeaborwa, P.D. Nsimama, R.E. (Ted) Kroon, Francis B. Dejene, J.J.(Koos) Terblans

*Corresponding author: [email protected] of Physics, University of the Free State, Bloemfontein, South Africa

Keywords : SrAl2O4:Eu2+, Dy3+, phosphor thin films, PLD, photoluminescence, diffusion

The afterglow property of SrAl 2O4:Eu2+,Dy3+ makes it a potential candidate for luminous paints on

highway poles, house numbering, rural lighting, etc. For industrial applications, thin films arepreferred due to better thermal stability, less out gassing and better adhesion to solid. Among thepopular thin-film preparation techniques, the pulsed laser deposition (PLD) technique has becomeincreasingly important because of its use of small targets, high deposition rate and capability of

forming thin films with proper stoichiometry [2]. Photoluminescence (PL) andcathodoluminescence (CL) properties of amorphous SrAl 2O4:Eu

3+,Dy3+ thin films prepared bypulsed laser deposition in vacuum, oxygen (O 2) and argon (Ar) atmospheres were investigated.Atomic Force Microscopy (AFM) was used to determine the topographical images of the films andthe PHI 700 Scanning Auger Nanoprobe was used to determine the elemental composition of thedifferent thin films. Auger electron spectroscopy and CL were used simultaneously to monitorsurface degradation under prolonged electron bombardment.

Long afterglow SrAl 2O4:Eu2+,Dy3+ thin film phosphors were successfully ablated on Si (100) substrates by the

pulsed laser deposition technique. AFM data (Figure 1 a and b) showed that the deposited thin filmswere packed with a uniform layer of nano grains. Better PL intensities were obtained from theunannealed nano structured films prepared in Ar and O 2 atmospheres with respect to the smoothlayers prepared in vacuum. Stable green emission at 515-520 nm, attributed to 4f 65d 1 4f 7 Eu2+ transitions, was obtained. After annealing the thin films at 800C, the CL intensity of the greenemission of the vacuum thin film increased considerably. The CL intensity of the Ar and O 2 thinfilms were almost completely quenched after annealing. The amorphous thin films were alsocrystalline after the annealing process. The desegregation of adventitious C on the surface of thesmooth vacuum layer and the nanostructures Ar and O 2 layers was responsible for the intensity

quenching. C was uniformly distributed throughout the Ar and O 2 thin films, Figure 1 (d), whileonly the top few nanometers of the vacuum films, Figure 1(c), contained C.

In the APPH ratios versus electron dose results, there were a decrease in C/O and an increase inSr/O and Al/O ratios with an increase in the electron dose. The C was removed from the film asvolatile species as a result of the Electron stimulated surface chemical reaction process. The CLintensity of the annealed film was very stable on further electron bombardment. TheSrAl2O4:Eu

2+,Dy3+ material can be considered to be one of the potential candidates for electronbeam operating device application based on its high stability to the electron bombardment.


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[1] H. Chander et al. , J. Cryst. Growth 271 (2004) 307.[2] K. B. Han et al. , Thin Solid Films 437 (2003) 285.

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Figure 1 : The AFM images and the AES depth profiles of SrAl 2O4:Eu2+,Dy3+ thin

films deposited in (a) and (c) vacuum and (b) and (d) Argon atmospheres,respectively, after annealing at 800 C for 2 hours.

(a) (b)

(c) (d)


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Figure 3: Pictures of glass ceramic samples :

(a) light emission observed under UV lampexcitation. After stopping UV irradiation, theafterglows of No. 5-1 were recorded at (b) 0s

and, (c)10 s, 1 min, 3 min, 5 min, 7 min and 9min.

Fabrication of long-lasting glass-ceramic phosphors O 04by melt-quenching method and their properties

Setsuhisa Tanabe 1,*, Takayuki Nakanishi 1,2, Yumiko Katayama 1, Jumpei Ueda 1

*Corresponding author: [email protected] University, Graduate School of Human and Environmental Studies, Kyoto, Japan2Hokkaido University, Graduate School of Engineering, Sapporo, Japan

Keywords : glass-ceramics, SrAl 2O4, europium, white LED

Glass-ceramic-based long-lasting phosphor was fabricated by quenching a melt of SrO-Al 2O3-B2O3 system doped with Eu and Dy. The SrAl 2O4 was the main and only crystalline phase and borateglass containing Sr and less amount of Al was the surrounding phase in the glass ceramics. Theglass ceramics showed long-lasting phosphorescence comparable to the LumiNova by Nemoto Co.Moreover, the glass ceramics showed excellentexcitation efficiency by 460nm excitation comparedwith the phosphos prepared by solid-state reaction.From the lattice constant, it is suggested that the Al 3+-sites in SrAl 2O4 crystals are partially substituted by B

3+ ions with smaller size. Thus the ligand field of Eu 2+ ionswas possibly modified by partial coordination of BO 4- tetrahedron in addition to the AlO 4- tetrahedron. Thepresent study proposes that the glass ceramicsfabricated have potential as new SrAl 2O4-basedphosphors for white LED excitation (~460 nm).

Figure 1: Compositional mapping images for maincomponent atoms: Sr, Al, O, Eu, by electron probemicroanalyzer (EPMA).

Figure 2: XRD patterns (27 31) of SrAl2O4crystals with different compositions. (a) Pure (no-doped) (b) Eu 2O3-doped (2 mol%), and (c) Eu 2O3 (2mol%) and B 2O3 (1wt%)-doped. The data of the glass

ceramics are also shown as (d).


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Luminescence studies of a combustion-synthesized O 05blue-green BaAl xOy:Eu

2+,Dy3+ nanophosphors

Francis B. Dejene

Corresponding author: [email protected] of Physics, University of the Free State (Qwa-Qwa campus), Phuthaditjhaba, South Africa

Keywords : BaAlxOy:Eu2+,Dy3+, nanophosphors, solution-combustion, structure, luminescence

Blue-green luminescent BaAl 2O4:Eu2+,Dy3+ phosphor powders were synthesized using the solution

combustion method. The effects of preparation conditions such the variation of amount of ureaand addition of boric acid as flux on the structural and luminescence properties of the powderswere investigated. The phosphors were characterized by X-ray diffraction (XRD), scanning electronmicroscopy (SEM) and fluorescence spectrophotometer. In the combustion reaction process, thecontents of urea determine the adiabatic temperature of combustion and the reactionsustainability which both influence the formation of BaAl 2O4 phase and photoluminescenceproperties. So, we investigated the effect of urea and boric acid content on the host phase, andprepared some samples with poor-fuel, stoichiometric, rich fuel and with or without boric acid.The representative SEM results of samples prepared without boric acid revealed nano sizedparticles (Fig. 1) and that the surface of the powder samples showed lots of voids and pores. EDS(electron diffraction spectroscopy) confirm the presence of the Ba, Al, O, Eu and Dy.

Figure 1: SEM micrographs of as-synthesized BaAl xOy:Eu2+,Dy3+ without boric acid

depict mixture of rod like and granular nanostructure.

The XRD results revealed changes in structure from BaAl 12O19 to a BaAl 2O4 single hexagonal phase.The dominant diffraction peaks index well with the card file (JCPDS:17-0306) in agreement withother reports [1].


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5 %

2 %

0 %

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u . )

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Figure 2: PL emission spectra ( exc= 325 nm) of BaAl xOy:Eu2+,Dy3+ phosphor fordifferent content of boric acid

The excitation spectrum of phosphors generally shows a broad-band spectrum extending from 250to 400 nm. The PL results, which are in good agreement with the XRD data, revealed a main peakat 496 nm and a shoulder peak at 580 for sample prepared without boric acid. The peaks are dueto the transitions from the lowest 2D level of the excited 4f 65d 1configuration to the ground 8S7/2 level of the 4f 7configuration of the Eu 2+ ion. It has been reported the emission spectrum of theBaAl2O4:Eu

2+,Dy3+ samples obtained by solid state method presented a main peak at 500 nm, anda shoulder peak at 435 nm. Compared to our results, it clearly exhibited a slight blue shift of thebroad band which might be caused by the quantum size effect [2]. Sample with boric acid showpeaks at 480, 580, 615 and 656 nm. It was observed that it also significantly reduces the intensityof blue emission while enhancing the red emissions. The decay characteristics show that theafterglow property was enhanced by the addition of B 2O3 [3]. The B 2O3 acts as an inert hightemperature solvent (flux) to facilitate the grain growth of barium aluminates. These increase thepenetration of trap centers in the ceramics and therefore achieve improvements in persistenceluminescence.

[1] X.Y. Chen et al. , J. Phys. Chem. C, 113 (2009) 2685.

[2] R. Stefani et al.

, J. Opt. Mater.

31 (2009) 1815.[3] A. Nag et al. , Mater. Res. Bull. 39 (2004) 331.


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Synthesis, persistent luminescence, and thermoluminescence O 06properties of yellow Sr 3SiO5:Eu

2+,RE3+(RE= Ce, Nd, Dy, Ho, Er, Tm, Yb)

and orange Sr 3-xBaxSiO5:Eu2+, Dy3+ phosphor

Jing Wang*, Baohong Li, Ye Li , Qiang Su

*Corresponding author: [email protected] of Education Key Laboratory of Bioinorganic and Synthetic Chemistry, State Key Laboratory ofOptoelectronic Materials and Technologies, School of Chemistry and Chemical Engineering, Sun Yat-sen University,Guangzhou, PR China

Keywords : rare earth, silicates, orange persistent phosphor

In the last decades, persistent luminescent materials have attracted much attention because theyhave significant practical and potential applications in many fields, e.g., emergent lighting, display,detection of high-energy rays such as UV, X- ray, -ray etc, and multidimensional optical memory

and imaging storage. Up to nowasday, the research interests worldwide have been mainly focusedon blue and green persistent luminescent materials based on Eu 2+ doped aluminates, silicates,aluminosilicates and oxides. Comparatively, the yellow, orange and especially red persistentluminescent materials with good chemical stability and excellent persistent luminescentperformance such as high brightness and long duration are in great scarcity.

In the present case, we develop a yellow Sr 3SiO5: Eu2+,RE3+(RE= Ce, Nd, Dy, Ho, Er, Tm, Yb) and an

orange Sr 3-xBaxSiO5: Eu2+, Dy3+ persistent luminescent phosphor and systematically characterized

them using XRD, photoluminescent excitation and emission spectra, persistent decay curve andemission spectra, and thermoluminescence spectra. The XRD results show that the structure of allSr3SiO5: Eu

2+,RE3+ samples was mainly coincident with Sr 3SiO5 and a solid solution of Sr 2.94- x Ba x Eu0.03Dy0.03 SiO5 were formed in the range of x=1-0.6. The photoluminescence properties showthat all phosphors can be efficiently excited by UV-visible light from 250 to 500 nm, and exhibitintense tunable emission from yellow-orange region toward orange-red region (570-591 nm). They


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Figure 1: The persistent emission spectra ( ex=370nm) of Sr 3SiO5:0.03Eu 2+,0.03RE 3+(RE= Ce, Nd, Dy, Ho, Er, Tm, Yb) and Sr 3-xBaxSiO5:

0.03Eu 2+,0.03Dy 3+ (x=0,0.05,0.1,0.2,0.4,0.6).

are due to 4f 5d and 5d4f allowed transitions of Eu 2+ ion. The yellow persistent luminescencestrongly depends on co-doped rare earth ion and its performance decreases in the order: Nd>Ho>Dy>Er>Tm>Ce> Yb and the persistent luminescence color can be finely tuned from yellow regiontoward orange-red region (557-591 nm) simply by modify the composition ratio of Sr 1-x/Ba x. Thethermoluminescence properties show that one peak is dominating at 367.5 K in Sr 3SiO5: Eu

2+,Dy3+ and is prominent at 351.5 K in Sr 2.74 Ba0.2Eu0.03 Dy0.03 SiO5, which are associated with the foreigndefects due to the aliovalent substitution of rare earth ions.

[1] P.F. Smet et al. , J. Electrochem. Soc. 156 (2009) H243-H248.[2] J. Wang et al. , J. Mater. Chem. 14 (2004) 2569-2574.[3] X. Sun et al. , J. Phys.D: Appl. Phys. 41 (2008) 195414-195417.


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Yellow persistent luminescence in Sr 2SiO4:Eu2+,Dy3+ O 07

Danuta Dutczak, Alexander Milbrat, Thomas Jstel*

*Corresponding author: [email protected] University of Applied Sciences, Steinfurt, Germany

Keywords : ortho-silicates, persistent phosphors

During the last decade, afterglow phosphors have attracted considerable attention due to theirpotential applications in various fields, including safety indication, light sources, graphic arts oroptical data storage. After the discovery of SrAl 2O4:Eu

2+,Dy3+ in the middle of the 1990tiesextensive research on different afterglow materials were conducted to tune their emission colorand to prolong their persistent luminescence properties. To this end, different synthesis methods,various co-dopants, and fluxes were investigated. However, these studies did not deliver efficientafterglow phosphors for the yellow to red spectral range.

Until now, the only efficient afterglow phosphors are blue to green emitting Eu2+

doped silicates oraluminates. Therefore, the development of an efficient yellow and red emitting afterglowphosphor is an ongoing challenge for solid state chemists. There are only few publications dealingwith yellow or red emitting afterglow phosphors and most of them show weak and rather shortpersistent luminescence.

This contribution deals with the Sr 2SiO4:Eu2+,Dy3+ yellow emitting afterglow phosphor and aims at

the improvement of its optical properties and the extension of its persistent luminescence.Sr2SiO4:Eu

2+,Dy3+ samples were prepared via a solid state and sol- gel method. The calcination wasperformed in a strongly reducing atmosphere comprising 30% N 2 and 70% H 2 at 1350 C.Sr2SiO4:Eu2+ exists in a monoclinic and an orthorhombic phase. The preparation via solid statemethod yields the orthorhombic phase, while the preparation by means of sol-gel method yieldsthe monoclinic phase. The UV and VUV excited luminescence at room and liquid nitrogentemperature, as well as, the decay times were recorded to characterize the synthesized samples.The most persistent luminescence has been observed for Sr 2SiO4:1%Eu

2+,0.5%Dy3+ crystallising inthe orthorhombic phase.

[1] N. Lakshminarasimhan et al. , Mater. Res. Bull. 43 (2008) 2946 2953. [2] Z. Pan et al. , J. Lumin. 129 (2009) 1105 1108.[3] J.H. Lee et al. , Mater. Sci. Eng. B 146 (2008) 99 102.


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Session II: Applications of persistent phosphors / Energy storage

O 08 What electron paramagnetic resonance spectroscopy teaches us 32about the structure of Eu 2+ centers in CsBr:Eu 2+ X-ray storage phosphorsHenk Vrielinck, Ghent University, Belgium

O 09 Influences and improvements on the brightness 34of industrial luminous afterglow products Bernhard Walfort, LumiNova AG

O 10 Elaboration of nanoparticles with persistent luminescence 35for in vivo imagingCline Rosticher, LCMCP Paris, France

O 11 Thermoluminescence characteristics of 37Lu2O3:Pr,Hf storage phosphor

Aneta Wiatrowska, University of Wroclaw, Poland

O 12 Evaluating the brightness of persistent phosphors: 39beyond the candelaDirk Poelman, Ghent University, Belgium

O 13 Water soluble afterglow nanoparticles for biomedical imaging 41and photodynamic therapyWei Chen, University of Texas, Arlington, USA


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What electron paramagnetic resonance spectroscopy teaches us O 08about the structure of Eu 2+ centers in CsBr:Eu 2+ X-ray storage phosphors

Henk Vrielinck 1,*,#, Dmitry Zverev 1, Paul Leblans 2, Jean-Pierre Tahon 2, Paul Matthys 1, FreddyCallens 1

*Corresponding author: [email protected]# Postdoctoral Fellow of the Flemish Research Foundation (FWO)1Ghent University, Department of Solid State Sciences, Gent, Belgium2 Agfa Healthcare NV, Mortsel, Belgium

Keywords : storage phosphors, photostimulated luminescence, CsBr, Eu 2+, EPR

Since the late 1990s Agfa has directed research efforts towards the development of a CsBr:Eu 2+ based X-ray storage phosphor for medical image plates (IPs) in computer radiography, that wouldsolve the resolution problems of the BaFBr:Eu 2+ powder IPs, while maintaining high sensitivity [1].

It was found that thermal evaporation of CsBr:Eu2+

on an Al substrate may result in orientedneedle growth (needle image plate, NIP), only a few m in diameter and up to several 100 m inlength (see Fig. 1), matching resolution and sensitivity requirements. This in itself is veryremarkable, as melt-grown Eu 2+ doped single crystals perform rather poor as photostimulatedluminescence (PSL) phosphor. It was further shown that a post-synthesis anneal at moderatetemperatures (180-200C), preferably in a humid atmosphere, improves the PSL sensitivity of theplates [2]. With the aim of understanding the PSL properties of CsBr:Eu 2+ NIPs and explaining thedifferences with large single crystals, we investigated these systems with electron paramagneticresonance (EPR) and electron nuclear double resonance (ENDOR). We focused attention on the

structure of incorporated Eu2+

centers. In this contribution, we review the results of these studies.

Figure 1: CsBr:Eu NIP : side (left) and top (right) view SEM image

In literature the decay of the Eu 2+-related EPR spectrum in CsBr at room temperature had beenattributed to the aggregation of oriented Eu 2+-VCs (Cs vacancy) dipoles with the formation oftrimers as an initial step [3]. Hackenschmied et al. [4] observed the XRD signature of additionalCsxEuyBrz phases in CsBr:Eu

2+ powders after annealing to 200C and a correlated increase of thesensitivity of the PSL phosphor. Later studies further recognized the significance of oxygen and/orwater in the annealing process, from which a hypothesis on the formation of Eu 2+-O2- self-compensating defect pairs emerged [5]. Eu 2+ trimer or Cs xEuyBrz phase formation in CsBr,

however, remain popular models for explaining the high PSL sensitivity of NIPs. Our EPR andENDOR study yielded two conclusions that put these literature hypotheses in another perspective.


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Our first conclusion concerns the Eu 2+ related centers in NIPs, which prove to differ substantially instructure from those in single crystals (both in aggregated and in isolated form), as is already clearfrom the comparison of their EPR spectra in Fig. 2. The intensity of the EPR spectrum of the NIPswas shown to be correlated with the plate sensitivity [5]. A detailed study of the temperaturedependence of the EPR spectrum, in combination with ENDOR at 3 K, enabled us to propose amodel for the centers, in which a Eu 2+ ion substitutes for Cs + and is accompanied by a H 2O

molecule and a V Cs at two of the nearest neighbor cation sites [6].

Figure 2: Q-band (34 GHz) EPR spectra of (a) CsBr:Eu 2+ NIPs at RT, (b) singlecrystals at RT with Eu 2+ in aggregated state, (c) NIPs at 20 K (B // ) and (d)single crystals heated to 820 K and quenched to 77 K at 20 K (B // ). Note

the difference in scale between left and right panels.

The second conclusion is about the Eu 2+ centers in CsBr single crystals. In agreement withliterature we find that isolated Eu 2+ centers, obtained after heating crystals to 820 K and rapidquenching to 77 K, aggregate at room temperature (RT). In contrast with earlier reports, however,the analysis of the angular dependence of the spectra clearly shows that these isolated Eu 2+ centers have cubic symmetry at temperatures down to 20 K. This either means that a chargecompensating V Cs near the Eu

2+ ion remains highly mobile at very low temperatures and produces

an effective cubic field via fast hopping, or perhaps more likely that a dominant fraction ofisolated Eu 2+ ions in CsBr have no V Cs in their vicinity.

The consequences of our findings on future research towards understanding and/or optimizingCsBr:Eu2+ NIPs will be discussed.

[1] P. Leblans et al. , Physica Medica , XV(1999) 301 304.[2] M. Weidner et al. , Radiat . Meas . 42 (2007) 661-664, and PhD thesis M. Weidner (2009).[3] V. P. Savelev et al. , Fizika Tverdogo Tela 16 (1974) 1090-1093.[4] P. Hackenschmied et al. , J. Appl . Phys . 93 (2003) 5109-5112.[5] S. Hesse et al. , Radiat . Meas . 42 (2007) 638-643.[6] F. Loncke et al. , Appl . Phys . Lett . 92 (2008) 204102.[7] H. Vrielinck et al. , Phys . Rev . B 83 (2011) 054102.


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Influences and improvements on the brightness O 09of industrial luminous afterglow products

Bernhard Walfort

Corresponding author: [email protected] AG, Teufen, Switzerland

Keywords : luminous products, improvement

Afterglow pigments are nowadays used in many products. Typical applications are in traffic- orsafety signs, instrument illumination or toy industry. Each of these applications have their specialrequirements to the pigment characteristics (excitability, decay behaviour, particle size, emissioncolour, body colour, etc.). The development and manufacturing of a very good glowing product isnot only possible by the use of a phosphorescent pigment with highest brightness, it is always alsoan interaction between the design of the product, the pigment characteristics and the processing

parameters.

The main design and processing parameters are:- type of chosen binder-matrix (varnish, binder, powder coating, plastic or pure powder)- application process used (filling, printing, extrusion, spraying, etc.)- design & layout (luminous area, layer thickness, mass of applied pigment, background

colour, etc.)

We will give an overview about:

- typical requirements asked from industry and a demonstration on selected examples howthese requirements can be fulfilled by adjustment of the pigment characteristics andprocessing parameters.

- products showing a satisfying performance- products and applications which are not suited for use of luminous afterglow pigments


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Elaboration of nanoparticles with persistent luminescence O 10for in vivo imaging

Cline Rosticher 1,*, Corinne Chanac 1, Bruno Viana 2, Aurlie Bessire 2

*Corresponding author: [email protected] Chimie de la Matire Condense de Paris - Universit Pierre et Marie Curie - UMR CNRS 7574 - Collgede France, Paris, France2Laboratoire Chimie de la Matire Condense de Paris - Universit Pierre et Marie Curie - UMR CNRS 7574 EcoleNationale Suprieure de Chimie de Paris, France

Keywords : persistent luminescence, in vivo imaging, nanotracers , silicate, oxisulfide

In the past decades, there has been a great improvement in the domain of the imaging systemsand new imaging tools have been developed. Optical imaging, in which photons are theinformation source, is a rapidly expanding field.

We aim at developing nanoparticles with persistent luminescence emitting in the red to near-infrared range for small animal imaging. The nanoparticles are first excited by a UV light for acouple of minutes outside the animal body, then injected to the animal, where they emit visiblelight for hours after the injection (figure 1). Autofluorescence, resulting from external illuminationduring signal acquisition, is therefore avoided.

Figure 1: a) particles in suspension are excited by UV light. b) The requiredquantity of liquid is taken then c) injected in an anaesthetized animal.

d) Acquisition of the signal coming from the animal can beginwithout any external illumination.

Different families of materials have been considered as host lattices for doping with transitionmetal and lanthanide ions: silicates and oxysulfides. Our starting material composition for thesilicate compounds was Ca 0.2Zn0.9Mg0.9Si2O6

[1] and to improve the emission in the infrared we nowdevelop Ca xMgySi2O6 (with x and y smaller than 1) compounds which were doped with the sameluminescent ions (Eu 2+, Dy3+, Mn 2+). Those are synthesized by a sol gel method. We are alsointerested in gadolinium oxysulfides doped by some luminescent ions such as Eu 2+, Ti4+, Mg2+. Theyare obtained by hydrothermal method and microwave route. All these compounds werecharacterized by Transmission Electronic Microscopy, X-Ray Diffraction, and their luminescentproperties were studied with a ICCD camera (photon-imager from Biospace).


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The final objective of this work is to obtain biocompatible and/or biodegradable nanoparticleswith the highest luminescence intensity and time.

In the end, we want to develop nanoparticles of doped calcium phosphates, which are the mostimportant inorganic constituents of biological hard tissues.

[1] Q. le Masne de Chermont et al. , Proc. Natl. Acad. Sci. USA 104 (2007) 9266 9271.


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Thermoluminescence characteristics of Lu 2O3:Pr,Hf storage phosphor O 11

Aneta Wiatrowska 1, Eugeniusz Zych 1,2, *

*Corresponding author: [email protected] of Chemistry, University of Wrocaw, Poland 2Wroclaw Research Centre EIT+, Wrocaw, Poland

Keywords : Lu2O3:Pr,Hf, storage phosphors, thermoluminescence

Thermoluminescence (TSL) is a thermally stimulated emission of light following a previousirradiation with visible, ultraviolet or yet more energetic photons [1]. The results obtained fromglow curves offer very usefull information about the possible interactions between the impuritiesand other defects enganed in the process. Lu 2O3 possesses a high density ( 9.42 g/cm

3) and higheffective atomic number (Z eff = 67.3) which makes it an attractive host for scintillators, X-ray and X-ray storage phosphors as it efficiently absorbs the high energy radiation.

The investigated materials, Lu 2O3:Pr,Hf were fabricated by the Pechini method using Lu 2O3, HNO3,Pr6O11 , HfCl4, citric acid and ethylene glycol. Raw powders were prepared at 700 C. These weresubsequently heat-treated at different temperatures up to 1700 C in different atmospheres for 5hours. Structural measurements proved that lutetium oxide activated with Pr 3+ ion and co-dopedwith Hf IV ion crystallized in cubic structure.

Figure 1: 3D graph of TSL of Lu2O3:0.05%Pr,0.1%Hf after exposure to X-Rays for 10minutes at room temperature. The heating rate was 4.8 C/s.

Figure 1 shows a 3D graph of TSL of Lu 2O3:Pr,Hf irradiated with X-Rays for 10 minutes. Thethermally stimulated luminescence (TSL) covers the range of 575 - 700 nm and corresponds to the1D2-

3H4,5 transitions within the Pr3+. Radioluminescence, photoluminescence, thermoluminescence

and optically stimulated luminescence spectra of Lu 2O3:Pr,Hf do not differ, practically.


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As seen in Fig. 1 at least three glow bands appear indicating that at least three different traps areactive in storing energy in Lu 2O3:Pr,Hf. The trap parameters: depth trap (E) and frequency factor(s) were calculated by fitting the glow curves with the general order kinetics model [2]. Analysis ofthe data will be presented. TSL intensity is strongly dependent on the synthesis conditions, whilethe shape of the glow curves is not. The highest intensity of thermoluminescence was observedfor materials prepared in reducing atmosphere at 1700 C. It was proved that this is Hf addition

which is crucial for the efficient permanent energy trapping in Lu 2O3:Pr.

Changes in thermoluminescence glow curves due to IR irradiation (980 nm and 780 nm) are givenin Fig. 2. Carriers from traps giving TSL at 110 C and 220 C were freed upon stimulation with 980nm radiation. 780 nm radiation removed additionally energy from the trap giving TSL around 245C. Yet, the trap producing TSL around 325 C was not affected by such radiation. More details willbe given in the presentation. Analysis of TSL properties of these materials will be shown andeffects of technological conditions will also be presented.

Figure 2: TSL glow curves of Lu2O3:Pr,Hf registered after exposure to UV radiation,and additionally stimulated with 980 nm (30 or 60 min)

or 780 nm (30 min) radiation. The heating rate was 4.8 C/s.

[1] S. W. S. McKeever, Thermoluminescence of solids, Cambridge Solid State Science Series, 1985[2] G. Kitis et al. , Nucl. Instr. Meth. Phys. Res. B 262 (2007) 313-322.


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Evaluating the brightness of persistent phosphors: O 12beyond the candela

Katrien Meert, Philippe F. Smet, Dirk Poelman*

*Corresponding author: [email protected], Department of Solid State Sciences, Ghent University, Belgium

Keywords : persistent phosphors, photometry, photopic, scotopic, mesopic, vision

Product specifications of persistent luminescent materials are based on their luminance at specifictimes after excitation or on the time until the luminance has dropped to a certain level (typically, avalue of 0.32 mcd/m 2 is used). However, this only allows a useful comparison of differentmaterials when they have a similar emission spectrum. Indeed, due to the shift of the human eyesensitivity towards lower wavelengths upon decreasing light intensity (the so-called Purkinjeeffect), a red-emitting material having the same luminance as a blue- or green-emitting material

will look much weaker under low level background illumination [1]. The aim of the present work isto gain a better understanding of the relation between measured luminance and perceivedbrightness of persistent luminescent materials and to find alternative variables to describe suchmaterials.

The human eye is a highly complicated instrument in which physical, photochemical andneurological effects influence the actual observation of brightness and colour. Under daylightconditions, cones are used for high spatial resolution and colour vision (the photopic regime),while at low-level light conditions, the much more light sensitive rods take over (the scotopic

regime). During twilight, in the so-called mesopic region, both rods and cones are active. Manyefforts are being made to describe human response in this intermediate region, since it is of majorinterest for optimizing illumination conditions in outdoor environments, like street lighting. Apartfrom having a different absolute sensitivity, spectral response and distribution over the retina ofthe eye, rods and cones sensitize or dark adapt in a different way and on a different time scale. Inview of all these elements, it is highly unlikely that the human eye response under all illuminationconditions can be modelled realistically with a limited number of parameters. Therefore, we havelimited ourselves to trying to describe the visibility of a persistent luminescent material in a simplebut realistic case: a person is light-adapted in a well lit room, when the electricity fails and the

person is left in complete darkness, except for a persistent luminescent sign [2].Starting from these assumptions, we have developed a simple visibility model, accounting for thedifferent spectral response of rods and cones and the shift from cone to rod vision upondecreasing luminance. In addition, the model takes into account the dark adaptation of the eye:when a test person is suddenly left in the dark, both rods and cones are still light adapted and theperson is virtually blind. During the first few minutes, the cones remain more sensitive than therods, and the visibility threshold is determined by the increasing cone sensitivity. After about 8minutes, the rod sensitivity surpasses that of the cones; this is called the rod -cone breakdown. Thepresent model explicitly uses the relative sensitivity of rods and cones at any time during the darkadaptation process to define a visibility index, which is assumed to give a better description ofthe observed brightness of persistent luminescent materials. Figure 1 shows both the measured


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Session III: Thermoluminescence / Persistent luminescence models

O 14 Thermoluminescence study of persistent luminescence fading 43in Sr2MgSi2O7:Eu

2+,R3+ materialsMika Lastusaari, University of Turku, Finland

O 15 Thermally stimulated luminescence: 45an algorithm for analyzing phosphorescence curves Eduardo Caselli, Universidad Nacional del Centro, Argentina

O 16 Charging behaviour in persistent phosphors 46Koen Van den Eeckhout, Ghent University, Belgium

O 17 Photoionization of lanthanide defects and how that affects 47luminescence and carrier storagePieter Dorenbos, Delft University of Technology, The Netherlands

O 18 Controlling trap depth to enhance persistent luminescence 49of silicate nanoparticles for in vivo imagingThomas Maldiney, UPCGI Paris, France

O 19 An x-ray absorption study of SrAl 2O4:Eu,Dy powders 51Katleen Korthout, Ghent University, Belgium

O 20 ZnGa 2O4:Cr3+: a new red long-lasting phosphor with high brightness 53 Aurlie Bessire, LCMCP Paris, France


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Thermoluminescence study of persistent luminescence fading O 14in Sr 2MgSi2O7:Eu

2+,R3+ materials

Hermi F. Brito 1, Jorma Hls 1,2,3 , Hgne Jungner 4, Taneli Laamanen 2,5, Mika Lastusaari 2,3,*,Marja Malkamki 2,5, Lucas C.V. Rodrigues 1,2

*Corresponding author: [email protected] de So Paulo, Instituto de Qumica, Departamento de Qumica Fundamental, So Paulo, Brazil2University of Turku, Department of Chemistry, Turku, Finland3Turku University Centre for Materials and Surfaces (MatSurf), Turku, Finland4University of Helsinki, Dating Laboratory, Helsinki, Finland5Graduate School of Materials Research (GSMR), Turku, Finland

Keywords : thermoluminescence, persistent luminescence, trapping, europium, disilicate

Sr2MgSi2O7:Eu2+,Dy3+ [1] with the blue persistent emission at 475 nm lasting for 24+ hours is one of

the most efficient persistent luminescence materials. Previous thermoluminescence (TL) resultshave shown that the shallowest, and simultaneously the main trap for each Sr 2MgSi2O7:Eu2+,R3+ material above room temperature is at ca. 0.7 eV below the conduction band corresponding to astrong TL maximum at ca. 90 oC [e.g. 2]. The combined results for the trap level energies, obtainedfrom the experimental data and density functional theory (DFT) calculations, suggested that themain trap responsible for the persistent luminescence of Sr 2MgSi2O7:Eu

2+,R3+ is created by chargecompensation lattice defects induced by the R 3+ co-dopants. The defects were tentativelyidentified as oxygen vacancies [2]. In this work, the fading of persistent luminescence fromSr2MgSi2O7:Eu

2+,R3+ (R: Y, La-Nd, Sm-Lu) was studied based on the TL and room temperatureluminescence measurements to gain more information on the persistent luminescencemechanism. The analysis of the TL glow curves was carried out by deconvolution with the programTLanal v.1.0.3 [3].

The glow curve analysis (Fig. 1) suggested second order kinetics for all the TL signals of thesematerials. For e.g. Sr2MgSi2O7:Eu

2+,Dy3+, the main TL peak consists of two traps at 0.63 and0.97 eV. The glow curves measured at different times after the irradiation show that the shallowertrap is emptied practically completely before the deeper one starts to be bleached to any extent.

The persistent luminescence fading was calculated with the second order decay model [4] usingthe single trap depth (E t), effective pre- exponential factor (s) and initial trap density (n0) valuesobtained from the TL glow curve deconvolutions. For e.g. Sr2MgSi2O7:Eu

2+,Dy3+, the calculatedpersistent luminescence decay for the shallower trap follows the experimental curve very welluntil ca. 60 min (Fig. 2). Beyond this point, which seems to coincide with the total bleaching of thisshallower trap, the experimental decay becomes faster than the calculated one. Contrary to this, itwould be expected that once the deeper trap starts to dominate, the fading would becomeslower. The results thus suggest that the decharging is then no longer controlled by isolated traps,but rather takes place via multiple interacting traps.

The results presented above together further data was used to discuss the details of the

mechanism of persistent luminescence for the Sr 2MgSi2O7:Eu2+

,R3+

materials.


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Figure 1: The deconvolution of the TLglow curve for Sr 2MgSi2O7:Eu

2+,Dy3+ after30 s UV irradiation. Inset: effect of fading(delay: 5 min 10 h) on the glow curve.

Figure 2: Persistent luminescence fadingfor Sr 2MgSi2O7:Eu

2+,Dy3+ (at roomtemperature) and that calculated fromthe TL data for the 0.63 eV trap based onsecond order kinetics.

Acknowledgments: Financial support is acknowledged from the Turku University Foundation, Jenny andAntti Wihuri Foundation (Finland) and the Academy of Finland (contracts #117057/2000, #123976/2006,#134459/2009 and #137333/2010). Dr. Kari O. Eskola (University of Helsinki), Dr. Janne Niittykoski(University of Turku, currently at OMG Kokkola Chemicals Ltd., Kokkola, Finland) and MSc Jukka Hassinen(University of Turku) are gratefully acknowledged for their help with the thermoluminescence

measurements.

[1] T. Lin et al. , J. Mater. Sci. Lett. 20 (2001) 1505-1506.[2] H.F. Brito et al. , J. Therm. Anal. Calorim. (2011), online: March 3, 2011.[3] K.S. Chung, TL Glow Curve Analyzer v. 1.0.3. , Korea Atomic Energy Research Institute and Gyeongsang

National University, Korea, 2008.[4] R. Chen et al. , Theory of Thermoluminescence and Related Phenomena , World Scientific, Singapore,

1997.

100 200 3000

1M

2M

3M

4M

100 2000.0

0.5M

1.0M

1.5M

UV irradiation 30 sHeating rate: 5 oCs -1

I n t e n s

i t y / C o u n

t s

Temperature / oC

Sr 2MgSi

2O

7:Eu 2+,Dy 3+

Delay 5 min 25 2 h 5 10

0.63 eV

0.97

0 100 200 300

1k

10k

100k

Observed (UV Irradiation 1 min) Calculated (2 nd order kinetics)

Sr 2MgSi2O7:Eu2+,Dy3+

P e r s i s

t e n

t L u m

i n e s c e n c e

I n t e n s i

t y / A r b .

U n i t s

Time / min


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Thermally stimulated luminescence: an algorithm O 15for analysing phosphorescence curves

Pablo Molina 1,2, Julin Marcazz 1,2, Marcelo Lester 1,2, Martin Santiago 1,2, Eduardo Caselli 1,3,*

*Corresponding author: [email protected] Universidad Nacional del Centro de la Provincia de Buenos Aires, Tandil, Argentina2Concejo Nacional de Investigaciones Cientficas y Tcnicas (CONICET), Buenos Aires, Argentina3 Comisin de Investigaciones Cientficas de la Provincia de Buenos Aires, La Plata, Argentina

Keywords : phosphorescence, curve analysis

Deconvolution of glow and thermally stimulated phosphorescence curves is a widely usedprocedure to find the parameters characterising luminescence mechanisms. Most of the employedmodels are derived from the set of coupled differential equations describing the adopted modelby resorting to the quasi-equilibrium approximation (QE approximation) and considering only a

trap and a recombination centre (OTOR model) [1]. This model has been extended to a modelhaving a thermally disconnected trap, i.e., a trap from which electrons cannot escape for thetemperatures a sample is subjected to (Mixed Order kinetics) [1]. A phenomenological model,dubbed General Order kinetics (GO), is frequently employed, but this model is not physicallymeaningful. Since most materials have two or more traps interaction among traps should beconsidered when it comes to understand the physics involved in the emission of light.

An algorithm is put forward which does not resort to the QE approximation and takes into accountinteractions among traps. The algorithm is based on a model consisting of several active traps, onerecombination centre a thermally disconnected trap. It is a generalization of the interactive multi-trap system [2, 3]. The analysis of phosphorescence curves by fitting the model to experimentaldata requires the integration of the set of coupled differential equations describing the traffic ofcarriers among the different centres (recombination and trap centres). Algorithms for fitting atheoretical model to experimental data, such as the Levenberg-Marquardt method, requires thatthe set of equations be integrated a large number of times, what renders the method unsuitablebecause of huge computational times. Further, on occasions, the solutions of the differentialequations can be unstable unless the step size of integration is taken to be extremely small(stiffness). The reported algorithm overcomes these difficulties.

[1] R. Chen et al. , Theory of Thermoluminescence and Related Phenomena , World Scientific, Singapore,1997.

[2] V. Pagonis et al. , Numerical and Practical Exercises in Thermoluminescence , Springer, 2006.[3] http://www2.mcdaniel.edu/Physics/TLwebsite/mathematicafiles.html
mailto:[email protected]://www2.mcdaniel.edu/Physics/TLwebsite/mathematicafiles.htmlhttp://www2.mcdaniel.edu/Physics/TLwebsite/mathematicafiles.htmlhttp://www2.mcdaniel.edu/Physics/TLwebsite/mathematicafiles.htmlmailto:[email protected]


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Charging behaviour in persistent phosphors O 16

Koen Van den Eeckhout*, Philippe F. Smet, Dirk Poelman

*Corresponding author: [email protected], Department of Solid State Sciences, Ghent University, Belgium

Keywords : charging, mechanism, MAl 2O4:Eu

During the excitation of a persistent phosphor, the intensity of the luminescence does notimmediately jump to a constant value. Instead, it rises gradually during several seconds or minutesbefore reaching its final value. This phenomenon is caused by the competition between trap fillingon one hand, and luminescence on the other hand. The more the excited electrons are beingtrapped, the less they are available for luminescence. Hence, in the beginning of the excitationprocess, when nearly all traps are empty, the trapping process dominates the luminescence, andthe intensity of the emitted light will be low. Clearly, the charging behaviour is closely related to

the traps present in the material.It is, therefore, surprising that so little investigations on charging behaviour have been reported[1-3]. These charging curves can learn us more about the amount and density of the traps, the rateat which electrons (or holes) are being caught, the trap depth, and possibly even their nature andorigin. In fact, the luminescence during charging is closely related to the afterglow of thephosphor, the only difference being the presence of an external excitation source. Hence, we canexpect to learn at least as much from charging behaviour as there is to learn from afterglowintensity.

We investigated the charging behaviour in the well-known SrAl 2O4:Eu,Dy and CaAl2O4:Eu,Ndphosphors, as a function of the excitation source, duration, and intensity. These measurementswere combined with afterglow and thermoluminescence measurements to study the amount oftraps being filled. The charging curves under intense laser radiation, where the luminescence ispractically saturated, were also measured, to investigate the concentrations of traps andactivators present in the material.

We will present some simple models for the involved processes, with greatly simplifiedassumptions, in order to explain some of the observed charging features.

[1] D. Jia, Optical Materials 22 (2003) 65.[2] Z. He et al. , J. Lumin. 119-120 (2006) 309.[3] X. Zhang et al. , J. Lumin. 128 (2008) 818.


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Photoionization of lanthanide defects O 17and how that affects luminescence and carrier storage

Pieter Dorenbos*, Adrie J.J. Bos

*Corresponding author: [email protected] Materials Research Group, Delft University of Technology, The Netherlands

Keywords : photoionization, lanthanides, tunneling

The mechanism active in persistent luminescence phopshors comprises the transport of chargecarriers through the lattice from a donor defect state to an acceptor defect state. In the case oftransport via the conduction band, an electron needs first to be exicted by daylight to energylevels within the conduction band, next the electron has to delocalize from its parent defect, andfinally it needs to be trapped by the electron accepting defect. This is the charge carrier storingphase. A reversed process by transport through the conduction band can be active in the

persistent luminescence phase. Alternatively when acceptor and donor defects are closeneighbors, charge carriers may be transferred between them if their final and initial states showsignificant orbital overlap, or otherwise a tunneling recombination pathways are thinkable.

From our recent investigations on the YPO 4:Ce3+;Ln3+ system we managed to study those charge

carrier delocalization phenomena [1,2]. This is illustrated in Fig. 1 for YPO4:Ce3+;Sm3+. After the

storage phase Ce 4+ and Sm 2+ are created. In Fig. 1 the Ce 3+ 5d-4f emission is monitored underoptical stimulation of Sm 2+. From the temperature and excitation wavelength dependencevaluable and unique information is obtained on the thermally activated release of electrons from

Sm2+

excited states that are located inside the conduction band. Also evidence for tunnelingrecombination in close pairs of Ce 4+-Sm2+ was obtained.

1.6 1.8 2.0 2.2 2.4 2.6 2.8

0.1

1

10

1004f 55d 1

d

b

SmB

I n t e n s i t y

[ a r b . u

n i t s ]

Energy (eV)

SmA

4f 5

5d 2

a

c

ef

gh

i

7F

0-

5D

0

Figure 1: OSL excitation spectra of Sm 2+ in YPO4:Ce3+;Sm3+ as function of

temperature. Spectrum a) is at 10K and spectra b) through i)are from 160 K to 300 K with 20 K interval.


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In this presentation the different charge carrier transport pathways and how they can be revealedby experiment will be reviewed. Possible relationships between electron delocalization. andluminescence excitation efficiency in ordinary phosphors are also addressed.

[1] P. Dorenbos et al. , Phys. Rev. B. 82 (2010) 195127.[2] A.J.J. Bos et al. , Radiat. Meas. 43 (2008) 222-226.


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Controlling trap depth to enhance persistent luminescence O 18of silicate nanoparticles for in vivo imaging

Thomas Maldiney 1, Aurlie Lecointre 2, Bruno Viana 2,*, Aurlie Bessire 2, Michel Bessodes 1, DidierGourier 2,Cyrille Richard 1, Daniel Scherman 1

*Corresponding author: [email protected] Unit de Pharmacologie Chimique et Gntique et d'Imagerie; CNRS, UMR 8151, Inserm, U1022, Universit ParisDescartes, Facult des Sciences Pharmaceutiques et Biologiques, Chimie Paristech, Paris, France.2 Laboratoire de Chimie de la Matire Condense de Paris; Chimie-ParisTech, UPMC, Collge de France, CNRS UMR7574, Paris, France

Keywords : diopside, lanthanide, electron traps, nanoparticles, in vivo imaging

In vivo optical imaging, using photons as primary information, has witnessed several majorimprovements in the last decades. In this field, we previously reported the synthesis of persistent

luminescence nanoparticles (PLNP) with formula Ca 0.2Zn0.9Mg0.9Si2O6:Eu2+

,Mn2+

,Dy3+

[1] andsharing the same crystalline structure as diopside CaMgSi 2O6 Such material possesses the ability tobe excited under UV-light before intravenous injection in mice, and to emit in the near-infraredwindow without further irradiation, circumventing autofluorescence from animal tissues. It wasdemonstrated that PLNP could be used as sensitiv

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