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Scintillation phenomenon in solids : History, principles, characteristics and
practical applications
Martin NiklInstitute of Physics, AS CR, Prague, Czech Republic
Internet search for the word “scintillator” provides
52,600 sitesusing Yahoo search engine …
…..but what is it good for ???
• Principle
• Something from their history
• Technology of preparation
• Underlying physics
• Parameters, characteristics and methods
• Applications
• An example of concerted research at aluminum garnets
• Suggested literature
Principle of a scintillator
10-12 10-10 10-8 10-6 10-4 0,01 1
wavelength [m]
infrared radio, TVmobile phones, etc.
visiblelight
VUV-UV
X-raysgamma
rays
1 photon n photons (keV - GeV) (2 - 4 eV)
scintillator Counting of HE photons!
Fast response needed !
Why we need it….above few keV there are no efficient direct-conversion detection elements (photon-to-electrical pulse)
Scintillation detector =scintillator+photodetector
⇒ registration of X-rays or γ-radiation, energetic particles or ions.
Scintillator TRANSFORMS high-energy photons into photons in UV/VIS spectral region, which one can easy and with high sensitivity register by the conventional detectors.
PD, APD, CMOS, CCD …Si, GaAs, GaN, InGaN, SiC, diamond
NaI:Tl
CsI:Tl
CdWO4
CsI
LiI:EuCaF
2 :Eu
1940 1960 1980 2000
CsI:Na
Bi4 Ge3 O
12
YAlO3 :Ce
BaF2 (fast)
Gd2 SiO
5 :CeCeF
3
PbWO4
Lu2 SiO
5 :Ce
LuAlO3 :Ce
Y3 Al5 O
12 :Ce
Lu3 Al5 O
12 :Ce
LaX3 :Ce(X=Cl,Br)
LuI3 :Ce
Lu3 Al5 O
12 :Pr
Year of introduction of a scintillation material
History of scintillatorsstarts short after the discovery of X-rays at the end of 19th century …
CaWO4
powder in 1896
Bulk single crystals
W.C. Roentgen, Science 3, 227 (1896)
chamber
carbon heater
carbon
Pt crucible
computercontrol
rotary pumpdiffusion pump 8inch-size BaF 2
Yoshikawa Lab, IMRAM, Tohoku university, Sendai, Japan
Czochralski technology
Czochralski grown YAlO 3:Ce, Lu3Al 5O12:Ce,
CRYTUR LtD. Turnov, CR
Czochralski grown PbWO4IP Prague, CR
Micro-pulling-down technology
After heater
Ir crucible
Seed crystal
Grown crystal
melt
<RF heating µµµµ-PD furnace>
Quartz tube
Ar
Alumina stage
Work coil
BaF2 crystal
φ1mm
φ3mm
Grown crystals
Yoshikawa Lab, IMRAM, Tohoku university, Sendai, Japan
Undoped YAP
Pr 0.1 mol%
Pr 0.5 mol%
Other solid state systems&technologies
LPE-grown single crystalline films,Y(Lu)AG:Ce,
Vapour deposited column-shaped CsI:Tl Diameter ~ 3
µm, length > 0.5 mm.
SrHfO3:Pb micro-crystalline phosphor
YAG-based optical ceramics
Ce-doped silica glass sol-gel technology(to make scint.fibers
Veronese Fr-1)
Physics of scintillators
CONVERSION TRANSPORT LUMINESCENCE
! Ecore<Eg
Conduction band
Eg
e
e
e e
h
h
h
h
traps
Valence band
Core band
HE
pho
ton
abso
rptio
n
CONVERSION -interaction of a high-energy photon with a material through photoeffect, Compton effect, pair production, appearance of electron-hole pairs and their thermalization
TRANSPORT - diffusion of electron-hole pairs (excitons) through the material, possible (repeated) trapping at defects, nonradiative recombination
LUMINESCENCE -trapping of charge carriers at the luminescence centre and their radiative recombination
Parameters, characteristics and methods
• Integral scintillation efficiency
• Photoelectron (Light) yield and Energy resolution
• Emission wavelength
• Speed of scintillation response
• Density (Zeff)
• Radiation resistance
• Chemical composition
• Price
Material with all the top parameters doesn’t exist so that there is always a search for tailored materials for particular applicationswhere only one or more parameters are recognized as the critical ones
Integral scintillation efficiency
0
5 104
1 105
1.5 105
2 105
2.5 105
3 105
300 400 500 600 700
Radioluminescence spectra (X-ray 35 kV, RT)
Bi4Ge
3O
12-standard
Gd2SiO
5:Ce
(Lu1.96
Y0.04
)SiO5:Ce
Inte
nsity
[arb
. uni
ts]
Wavelength [nm]
Absolute comparison of radioluminescence spectraof a material with the standard samplein the same experimental conditions
0
1 104
2 104
3 104
4 104
5 104
6 104
350 450 550 650 750
Radioluminescence spectra (X-ray 35 kV, RT)
BGO standard
PbWO4 no.178b
PbWO4 no.178f
Inte
nsity
[arb
. uni
ts]
Wavelength [nm]
Integral efficiency η=β.S.Q equals to multiplied sub-efficiencies of the conversion, transport and luminescence stages
Photoelectron (Light) yield
1
10
100
1000
0 500 1000 1500
Photoelectron yield of YAP:Ce
Excitation - 662keV photons (137Cs)
num
ber
of p
ulse
s/ch
anne
l
no. of channel
∆∆∆∆A
A0
energetic resolution = ∆∆∆∆A/A0
photopeak
Compton edge
Light yield measurement consists in the measurement of the charge collected at the photomultiplier anode within certain time gate(typ. 1 µs), i.e. U.I.∆∆∆∆t, after the absorption of high energy photon. Result of measurement is scaled within multichannel analyzer memory (pulse height analysismode) and repeated many times to get reasonable statistics and well-resolved photopeak (obtained only if complete absorption of HE photon can be obtained in the sample, i.e. sufficiently big sample is needed).
Energy resolution is defined from the FWHM of the photopeak. (typical values are 5-15% at 662 keV)
Photoelectron yield divided by quantum efficiency of photocathode providesLight yield - given in [photons/MeV]the best classical materials as NaI:Tl,CsI:Tlgive 40 000-50 000 phot/MeV , BGO gives 8 000 phot/MeV.
Photoelectron (light) yield nonproportionality
The non-proportionality of the Nphels(E) photoelectron yield of LuAG:Pr Cz-grown crystal normalized to Nphelsyield of 137Cs 662 keV energy line
See also Vasil’ev Mo-3, Moszynski Tu-13
Photoelectron yield value (per MeV) depends on the energy of the incoming HE photons !!
Conversion of high energy photon into many electron-hole pairs at the end of Conversion stage is many-step process with non-unique pathway. Elementary steps are differing in “production yield” of final e-h pairs, closely spaced excitations may interact, material defects make it even more complex, etc.
Emission wavelength versus photodetector spectral response
0
0.4
0.8
200 400 600
Radioluminescence spectra :CeF
3 (a), YAlO
3:Ce (b) Lu
3Al
5O
12 (c)
Inte
nsity
[arb
.uni
ts]
Wavelength [nm]
a b
ground statesplitting
of Ce3+
c
Position of the emission spectrum is important for the choice of the photodetector. In the case (a) PMT with quartz window (more expensive) is needed, (b) is an optimum position for a standard S20-photocathode PMT, (c) is better suited for a photodiode (or CCD) detector.
Today, however, there is tremendous development of UV-sensitive semiconductor photodetectorsbased on SiC, GaAlN and diamond!
Optical coupling between scintillator and photodetector
By far not all the UV/visible light generated in scintillator can be delivered to the photodetector due to self-absorption, internal reflection, scattering losses, etc.
1 µµmm
Si mold
Patternedpolymer
GaNdiode struct.
Photonic bandgap on the surface for better light extraction !!
Speed of scintillation response
1 photon n photons (keV - GeV) (1 - 6 eV) I(t) = ΣA iexp[-t/τi]
t
I(t)
t0 t0 t
I(t)
scintillator
Duration of the output light pulse is determined by the luminescence decay time of the emission centers, but also by the timing characteristics of the transportstage
Examples of scintillation decay
0.001
0.01
0.1
1
0 100 200 300 400 500 600 700
PL decay, exc = 335 nmScint.decay, exc = 511 keV
inte
nsity
[arb
.uni
ts]
time [ns]
decay times:60-70 ns
54 ns
LuAG:Ce0.12%
IS
Itot
alpha = IS/I
tot x 100%
600-900 ns
time
excitation
emission
50µs
“Background increase” due to slow decay components in scint. decay
10
100
1000
0 200 400 600 800
LYSO:Ce Photonics
Inte
nsity
[arb
. uni
ts]
time [ns]
decay time:45 ns
In Ce-doped scintillators the shallow electron trapsare responsible for s lower scint i l lat ion components
Trapping-detrapping Processes
Ionizing radiation
(X, γ…)
Valence band
Conduction band
Lground
hνRadioluminescence
A – direct process
T
B – delayed process
ET
e
h
Lexc
Studied by TSL and TSC experiments (lectures in next days)
Radiation damage (resistance)
0,2
0,6
1
1,4
0
0,4
0,8
1,2
300 400 500 600 700
Absorption spectra of YAP:Ce
abso
rban
ce
lumin. intensity
wavelength (nm)
absorption spectrabefore (A
0) and
after (Airr
) X-ray irradiation
(dose 500 Gy)
luminescence spectrum
Induced absorption is caused by the relocation of charge carriers into the deep traps(can be monitored by TSL measurement above RT). Occupied deep traps introduce the additional=induced absorption bands (color centers).
In the case of YAP:Ce such traps can be partly suppressed by tetravalent Zr4+ ion doping.
0
0,4
0,8
1,5 2 2,5 3 3,5 4
Induced absorption spectrum µ(λ)YAP:Ce, D=500 Gy, RT
ia (cm-1)
G1 ia (cm-1)
G2 ia (cm-1)
G3 ia (cm-1)
G1+G2+G3
ia (
cm-1
)
E (eV)
µ(λ) = 2.3×(1/l )×(A irr (λ) - A0 (λ))
Lu2SiO5:
Ce
Bi4Ge3O12Lu3Al5O12:Ce
YAlO3:
Ce
PbWO4LaBr3:CeCsI:TlChem.Compos.
7.417.136.67 5.368.235.084.51Density
g/cm3
40/--/30055-65/
500-103
20-38/
100-104
2+10/
100-104
16/
--
--/1000Decay tm
[ns]
Fast/slow
2.7-3.2x104
8x1031.5-1.9x104
~2x1041-3x1026.3x1044-5x104LY
Pho/MeV
Fast/slow
420490530-580360-380410/500380400/565Emission
Max.[nm]
Fast/slow
Parameters of selected scintillation materials
High energy physics
Particle physics, Particle physics, ……
X&Neutron-based
Remote detectionRemote detection
Medical application
PET, SPECT, CTPET, SPECT, CT
Security check
XX--ray scanningray scanning
Other applications
Radon detection, geologyRadon detection, geologyComputed tomographyComputed tomography
Nondestructive analysis
Applications of Applications of scintillatorsscintillators
Checking point
Detector ring (inner diam. ~ 0.8 m)
PositronEmissionTomography
Collinearly emitted annihilation quanta detected in coincidence
DetectorsBGO + PM
Radiation in Medicine Diagnostics Radioisotope imaging
Radiopharmaceutical
Coming Lu(Gd)2SiO5:Ce TOF, DOI modifications under development
http://www.epub.org.br/cm/n01/pet/pet_hist.htm
PET systemsSiemens-CTI
Simultaneous PET and MR imaging
1D positionsensitivedetector(rotating)
X-rayComputedTomography
3rd generation
X-ray fan beam (rotating)
X-ray source(rotating)
Centre of rotation
Radiation in Medicine Diagnostics
+
Typical X-irradiation dose in a CT scan is 20x higher than that of simple lung check ….should be used with caution!
CT – „whole body“ spiral scan
my knees
Security check … by far not only luggages!
�About 200 millions of containers travel every year, and only about 1 to 2 % of them are directly controlled !!!
�Check for drugs, explosives, radioactive material at seaports and airports HOMELAND SECURITY!!!
� multiple irradiation sources(X-ray, neutrons)
� sensitive not only to material density, but also to its elemental composition (explosives)
� on-line evaluation of moving goods
� mobile stations with short installation times
� easy to handle and use
Remote detectionRemote detection
Checking point
irradiation source detector
•high light yield and mechanically/chemically stable scintillator for X-ray detection
•tuned-composition (Li-B-Gd containing) material for neutron detection
Compact Muon Solenoid detector in Large Hadron Collider in CERN, Geneva
PbWO4-based calorimetric detector
search for Higg’sboson ……
about 80,000 single crystal blocksof about 3x3x22 cm (12 m3 ) produced in Russia and China, LHC launch expected 10/2009!
High resolution 2D-imaging experiment under X-ray (accelerated electrons)
X - Ray (Lu)YAG:Ce CCDX - Ray (Lu)YAG:Ce CCD
thin YAG:Ceplate
thin optical glue
glass support
Sub-µm resolution needed!
Better 2D-resolution requires thinner scintillator layer !
optics
Made by CRYTUR Ltd, CR
Scintillator screens, experimental set-up
LPE-grown LuAG:Ce-on-YAG films and single crystal plate on substrate
Experimental set-up for 2D imaging
Whole LPE film on one side and 5 µm on the other side were polished away
X-ray source
X-ray cameraobject
7067616210092
0.50.50.50.533
172915272020
LuAG:CeLuAG:CeLu0.8Y0.2AG:CeLu0.6Y0.4AG:CeLuAG:CeLuAG:Ce
LPE SCFLPE SCFLPE SCFLPE SCFBulk CzBulk Cz
Lu-6Lu-9Lu-11Lu-16Cz-2Cz-3
Scintil. eff[%]
Substrate [mm]
Film/plate[µµµµm]
Film/plate material
Sample type
Sample name
Overview of the scintillator screens used
2D imaging capability of LPE films and SC plates
SEM image of 8 µµµµm thick wire grid
The grid image obtained by Lu-6 sample screen (upper left) with the detail of wire crossing (lower left) and the same picture obtained by Cz-3 sample screen (right)
Some more images by SC LuAG:Ce plate sensor
A circuit fromcalculator
A tick
Aluminum structure
Coaxial cablewith BNC connector
Strategy for scintillator materials researchCorrelation of several techniques at specifically prepared sample set under well-defined technological conditions:
�Time-resolved emission spectroscopy– to interconnect the luminescence (scintillation) kinetics with the occurrence or non of the defects visualized by the above techniques
�Specific experiments for determination of scintillation characteristics (Phel. yield, scintillation decay, radiation damage)
�Thermoluminescence– to visualize trapping states, which take part in the radiative processes, spectra can advise on recombination sites
�Thermally stimulated currents– to visualize complementary nonradiative processes
�Electron paramagnetic (spin) resonance– to understand location of unpaired-spin-containing trapping centers
Integral eff. & LY in Ce3+-doped Y3Al5O12 and Lu3Al5O12
0
5 104
1 105
1.5 105
2 105
2.5 105
3 105
3.5 105
4 105
200 400 600
YAG:Ce0.32%LuAG:Ce0.12%BGO x5
Inte
nsity
(ar
bitr
ary
units
)
Wavelength (nm)
x5
X-ray excitedluminescence Light yield (1 µs time gate)
Best YAG:Ce∼ 3x BGO
Best LuAG:Ce∼ 60% of YAG:Ce
A lot of “slow light”in these materials
Retrapping of electrons at shallow traps before their radiative recombination at Ce3+ ionsNikl et al, pss (a) 201, R41 (2004)
10
100
1000
600 1000 1400 1800
inte
nsi
ty [
arb
.un
its]
time [ns]
LuAG:CeScintillation decay pulsed x-ray, em = 500 nm
58 ns (30%)
150 ns + 600 ns (70%)
Ce-doped YAG and LuAG
0
1 106
2 106
3 106
4 106
5 106
6 106
7 106
8 106
50 100 150 200 250 300
TS
L in
tens
ity (
arb.
uni
ts)
temperature (K)
LuAG:Ce0.12%TSL after X-rayirr. at 10 K
YAG:Ce0.32%
0.001
0.01
0.1
1
100 200 300 400 500 600 700
PL decay, exc = 335 nmScint.decay, exc = 511 keV
inte
nsity
[arb
.uni
ts]
time [ns]
decay times:60-70 ns
54 ns
LuAG:Ce0.12%
levels of YAG:Ce0.32%
A number of the electron traps indicated by TSL glow curve below RT delays electron delivery to Ce4+ and slows down the scintillation response
time
excitation
emission
50µs
“Background increase” due to slow decay components in scint. decay
Antisite defects in YAG and LuAG single crystals
Exchange of Y(Lu) and Al ions is an inevitable consequence of the growth from high temperature melt
CB
VB
Electrontrap
0
0.6
1.2
1.5 2 2.5 3 3.5 4TS
L no
rm. i
nten
sity
Energy (eV)
T=92 K
Comparison of YAG:Cesingle crystal and optical ceramics
0.0 100
1.0 107
2.0 107
50 100 150 200 250 300
single crystal
ceramics
TS
L in
ten
sity
(a
rb.
un
its)
Temperature (K)
TSL peak at 92 K is the dominant feature in all YAG:Ce single crystals studied
Sintering temperature of ceramics is about 1700 0C applied for several hours, while SC growths from the melt close to 1970 0C
Concentration of YAl antisitedefects strongly decreases with preparation temperature(absent in LPE-grown layers – Zorenko et al, Funct. Mater. 9, (2002) 291 )
TSL glow curve X-ray irr. at 10 K
TSL spectra
∆E = 0.18 eV
Mihokova et al, J.Lumin.2006
TSL peak at 92 K is due to liberation of electron from the antisite YAl
defect trap and recombination with Ce4+ hole center.
Ce3+ 1µµµµm
Electron traps related to the antisite LuAl
defects in LuAG:Ce
102
104
106
50 150 250
SC-1820SC-1700LPE-9300LPE-18000
TS
L in
tens
ity (
arb.
uni
ts)
Temperature (K)
TSL glow curves Triple peak structure at 142 K, 167 K and 190 K is always dominant in single crystals,
while it is completely absent in Liquid Phase Epitaxy-grown layers.
TSL spectra within these peaks contain only Ce3+ emission
Liberation of electrons from the antisite-defect-related trap and their recombination with Ce4+ is proposed to explain TSL characteristics in this temperature region
Nikl et al, phys.stat.sol. (b) 242, R119 (2005)
∆E =0.29 eV0.40 eV0.47 eV
As the energy depth of AD-related trap is higher with respect to YAG:Ce, it explains more detrimental influence on scintillation decay and LY characteristics!!
Antisite defects in Al garnetsHigh-resolution spectroscopy of the Nd3+
satellite emission lines in YAG:NdLupei et al., Phys. Rev. B 51, 8 (1995)
XRD from an increase of lattice constant in YGG:Yb single crystal and ceramicsShirinyan et al, NIM A 537 (2005)
Newly by EPR evidenced Ce3+Al and
Ce3+ perturbed by LuAl centers!
Laguta et al, LUMDETR 2006, Lviv
200 300 400 500 600 700 800
B (mT)
Ce3+ in bulk LuAGB II [110], T=20 K
Ce3+⇒ Lu3+
Ce1Ce2 Ce3
Ce3+ at Lu site perturbed by the LuAl antisite defect ⇒ Ce and LuAl
defect might be spatially correlated!!
Ce2, Ce3 belong to the Ce3+ at Al sites
TSL dependence on the Ce concentration in LuAG:Ce – region 1 and 2
0
1
50 150 250
0.12w%Ce0.07w%Ce0.03w%Ceundoped
TS
L in
tens
ity (
arb.
uni
ts)
Temperature (K)
undopedx 20
TSL glow curves
Diminishing of “undoped-related”TSL features within 50-80 K with increasing Ce concentration
Competition between TSL signals within 50-120 K and 120-200 K !
After X-ray irradiation at any T ∈ (10-100) K phosphorescence decay doesn’t depend on temperature and follows t-1 law
Tunneling processbetween the trapped electron and hole counterparts (spatially correlated)
104
106
108
1010
1012
1014
1016
10 100 1000 10000Pho
spho
resc
ence
inte
nsity
(ar
b. u
nits
)
Time (s)
100 K
90 K
80 K
70 K60 K
50 K40 K30 K
20 K10 K
I(t) ∼∼∼∼ t -p
1.00
0.99
1.021.031.091.13
1.071.09
1.17
1.11p =
Scintillation decay of LuAG:Ce at RT
100
1000
0.12w%Ce power-exp fit I(t)
Inte
nsity
[arb
.uni
ts]
I(t) = 0.175exp[-t/56.4ns]+
+ 1.7/(60+0.24ns*t)-0.998+43
-3
-2
-1
0
1
2
10 100 1000
power+exp. fit2-exp. fit
wei
ghte
d re
sidu
als
R(t
)
time [ns]
0
2
4
6
0 0.04 0.08 0.12
coef
ficie
nt a
lph
a
concentration Ce [w%]
The exponential and power function components account for the first and second stage of the scintillation decay, respectively.
Consideration of tunneling-driven recombination provides a physical ground for the slower scintillation decay component in LuAG:Ce, which can’t be explained by thermal detrapping and recombination via conduction band as calculated detrapping times are too long.
Instead, coefficient alpha and amplitude of the 140 K TSL peak seem to be correlatedand related to the time development of recombination processes at similar time scales
Radiative recombination process in LuAG:Ce (Pr)
CB
VB
Ce3+
(Pr3+)
At RT τ > 30 µs
~ t-1
AD-related electron
trap
Above 50 K there is possibly already
thermally assisted tunnelling process
(slight T dependence of p)
hν
Admixture of Ga to suppress AD-related trapping phenomena in LuAG:Pr (Ce)
0
1 105
2 105
3 105
4 105
5 105
6 105
7 105
200 300 400 500 600
Radioluminescence spectra LuAG:Pr (0.25%)
85 K
295 K
Inte
nsity
[arb
. uni
ts]
Wavelength [nm]
host
Pr3+
0
2 104
4 104
6 104
8 104
1 105
200 300 400 500 600 700
RT-193C
Inte
nsity
[pho
t/s]
Wavelength [nm]
Lu3(Ga
0.05Al
0.95)5O
12:Pr
0 100
2 106
4 106
6 106
50 150 250
TSL glow curves, x-irradiation at 10 K
x = 0
x = 0.1
x = 0.2
x = 0.4
TS
L in
tens
ity
Temperature [K]
Lu3(Ga
xAl
1-x)5O
12:Pr3+
0.01
0.1
1
0 200 400 600
Lu3Al
5O
12:Pr 1%
Lu3(Ga
0.4Al
0.6)5O
12:Pr1%
2-exp. fit I(t)
inte
nsity
[arb
.uni
ts]
time [ns]
I(t) = 0.58exp[-t/10.4ns ]+0.96exp[-t/21.3ns ]+0.013
Scintillation decay at RT, 22Na
Nikl et al, Appl.Phys. Letters 88, 141916 (2006)
Energy transfer and storage in LuAG:Ce(Pr) SC
�Electron traps associated with LuAl antisite defectswere evidenced in LuAG host. TSL triple peak at 142 K, 167 K and 190 K (region 2) is due to electron libration from LuAl trap and its recombination with the Ce4+ (Pr4+) hole center. In YAG host an analogous situation holds for 92 K TSL peak.
�EPR evidences a possibility of spatial correlation of Ce3+ and LuAl defect, which is reflected in the existence of tunneling process observed in TSLglow curves (region 1) supported by the t-1 course of low temperature phosphorescence decay.
�TSL process thus indicates the existence of both thermally activated “above-the-gap” (region 2) and “sub-gap tunneling” (region 1) recombination processesbetween an AD-trapped electron and Ce4+ (Pr4+) hole center, where the latter process is responsible for the observed slower component in the scintillation decay.
� Ga-admixture considerably diminished the AD-trap related phenomena: host luminescence suppressed, TSL peaks washed out, scintillation decay accelerated. However, it seems that LuAl defects could be “burried” in the lowered bottom of CB rather than simply suppressed due to the Ga occupation of the Al octahedral site. Somewhat lowered LY and form of the Pr3+ excitation spectra within 170-200 nm might indicate an additional nonradiative loss channel induced by the Ga doping.
Perspectives�Sources of energetic radiation and particles are more and more used in different fields of human activity ⇒ increasing need fortailoredscintillation materials
�Difficult to “invent” competitive completely new materials as in some parameters we are close to intrinsic limits, but new technologies (ceramics) can bring unexpected solutions
�Lack of the detailed understanding the physical mechanisms in existing materials ⇒ room for their optimization(recent example of PbWO4)
�Driving forces for scintillator development will come from medical and high-tech industrial applications, homeland security, space technology
Suggested literature• G. F. Knoll: Radiation Detection and Measurement (Wiley, New York 2000)• G. Blasse, B. C. Grabmaier: Luminescent Materials (Springer, Berlin 1994)• P. A. Rodnyi: Physical Processes in Inorganic Scintillators (CRC Press, Boca
Raton 1997)• L. H. Brixner: New X-ray phosphors, Mater. Chem. Phys. 16, 253-281 (1987)• M. Ishii, M. Kobayashi: Single crystals for radiation detectors, Prog. Cryst.
Growth Charact. Mater. 23, 245-311 (1992)• C. W. E. van Eijk: Inorganic-scintillator development, Nucl. Instrum. Methods
Phys. Res. A 460, 1-14 (2001)• M. J. Weber: Inorganic scintillators: today and tomorrow, J. Lumin. 100, 35-45
(2002)• M. Nikl: Scintillation detectors for x-rays, Meas. Sci. Technol. 17, R37-R54
(2006)• D. J. Robbins: On predicting the maximum efficiency of phosphor systems
excited by ionizing-radiation, J. Electrochem. Soc. 127, 2694-2702 (1980)• A. Lempicki, A. J. Wojtowicz, E. Berman: Fundamental limits of scintillator
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