ZnGa2S4 as a host for Eu2+ -activated luminescence

LumiLab

Department of Solid State Sciences

Ghent University

IWASOM, July 16, 2013

ZnGa2S4 as a host for Eu2+-activated luminescence

Jonas Joos, Katleen Korthout, Dirk Poelman, Philippe Smet

Jonas Joos ZnGa2S4 as a host for Eu2+-activated luminescence

Conversion phosphor White LEDs

Jonas Joos ZnGa2S4 as a host for Eu2+-activated luminescence Jonas Joos ZnGa2S4 as a host for Eu2+-activated luminescence

1

EBU gamut

Planckian locus

v.s.

Jonas Joos Green phosphors for high brightness applications

Conversion phosphor Improved efficiency for displays


SrGa2S4:Eu2+

EuGa2S4

CaGa2S4:Eu2+

SrSi2O2N2:Eu2+

β-SiAlON

2

EBU gamut

Planckian locus

v.s.


Conversion phosphor Improved efficiency for displays


SrGa2S4:Eu2+

EuGa2S4

CaGa2S4:Eu2+

SrSi2O2N2:Eu2+

β-SiAlON

2


Zn1-xEuxGa2S4

A small biography

“ZnGa2S4:Eu2+ medium intense green phosphor.” -- M. M. Yuta, W. B. White

1992


3


“ZnGa2S4:Eu2+ medium intense green phosphor.” -- M. M. Yuta, W. B. White

A small biography


Zn1-xEuxGa2S4

3


“The PL spectrum of ZnGa2S4:Eu,F consists of a broad band at 565 nm.” -- B.G. Tagiev et al.

2000

A small biography


Zn1-xEuxGa2S4

3


2005

A small biography


“…lead to the assumption that the Eu2+ ions are substituted at octahedral voids of the host lattice rather than at cationic sites.” -- C. Wickleder et al.

Zn2+ / Ga3+

S2-

Eu2+

Zn1-xEuxGa2S4

3


“…lead to the assumption that the Eu2+ ions are substituted at octahedral voids of the host lattice rather than at cationic sites.” -- C. Wickleder et al.

A small biography


Zn2+ / Ga3+

S2-

Eu2+

Zn1-xEuxGa2S4

3


“High PL intensity at 540nm.” -- J. W. Kim, Y. J. Kim

2007

A small biography


Zn1-xEuxGa2S4

3


“… a good candidate for prospective solid state lighting devices.” -- Y. Jeong et al.

2012

“… the ZnGa2S4:0.05Eu2+ phosphor can be a good green phosphor candidate … “ -- R. Yu et al.

A small biography


Zn1-xEuxGa2S4

3


4th IWASOM Gdańsk 2013

Critical evaluation of luminescent properties

Where is Eu2+ ?

A small biography


Zn1-xEuxGa2S4

3


Diffuse reflectance

Steady-state photoluminescence

Photoluminescence

ZnGa2S4 Zn0.99Eu0.01Ga2S4 EuGa2S4


excitation emission

Zn1-xEuxGa2S4

4


Quantum efficiency

Photoluminescence

Ab

sorp

tio

n –

Qu

antu

m e

ffic

ien

cy


Absorption Internal QE External QE

Zn1-xEuxGa2S4

5


Thermal quenching and decay

Intensity Lifetime

Independent of doping concentration


Zn1-xEuxGa2S4

6


Stating the hypothesis

PL spectra Zn1-xEuxGa2S4 and EuGa2S4 very similar

Absence of concentration quenching

TQ and decay independent of x


Zn1-xEuxGa2S4

7


Stating the hypothesis

PL spectra Zn1-xEuxGa2S4 and EuGa2S4 very similar

Absence of concentration quenching

TQ and decay independent of x

EuGa2S4 responsable for luminescence?


Zn1-xEuxGa2S4

7


SEM-CL-EDX

Cathodoluminescence spectroscopy inside SEM

Relate luminescence to chemical composition (EDX)


Zn1-xEuxGa2S4

8


SEM-CL-EDX




Zn1-xEuxGa2S4

8


SEM-CL-EDX



ZnGa2S

4 Zn

1-xEu

xGa

2S

4 EuGa

2S

4


Zn1-xEuxGa2S4

8


X-ray diffraction

Emerging of EuGa2S4 peaks visible

Zn0.94Eu0.06Ga2S4

ZnGa2S4


Zn1-xEuxGa2S4

9


X-ray diffraction


Zn0.94Eu0.06Ga2S4

ZnGa2S4


Zn1-xEuxGa2S4

9


X-ray diffraction


Zn0.94Eu0.06Ga2S4

ZnGa2S4


Zn1-xEuxGa2S4

9


X-ray diffraction


Region around ±24° inspected

Amount of EuGa2S4 as function of Eu-concentration


Zn1-xEuxGa2S4

9


X-ray diffraction



Amount of EuGa2S4 as function of Eu-concentration


1.0

EuG

a 2S 4

co

nte

nt

No incorporation

x

Zn1-xEuxGa2S4

9


X-ray absorption spectroscopy

Zn K-edge in Zn0.96Eu0.04Ga2S4

Eu LIII-edge in Zn0.96Eu0.04Ga2S4

Eu LIII-edge in EuGa2S4

EXAFS @ ESRF Grenoble (FR)


Zn1-xEuxGa2S4

10




Eu2+ does not occupy Zn-site


Zn K-edge in Zn0.96Eu0.04Ga2S4

Eu LIII-edge in Zn0.96Eu0.04Ga2S4

Eu LIII-edge in EuGa2S4

Zn1-xEuxGa2S4

10




Where is Eu2+ ?

A small biography


Zn1-xEuxGa2S4

11




ZnGa2S4:Eu2+ unsuitable as conversion phosphor

Where is Eu2+ ?

A small biography


Zn1-xEuxGa2S4

11





Where is Eu2+ ?

Majority inside EuGa2S4 impurity phase!

A small biography


Zn1-xEuxGa2S4

11




Where is Eu2+ ?

Majority inside EuGa2S4 impurity phase!

A small biography


Zn1-xEuxGa2S4

11

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Thanking…

LumiLab

Department of Solid State Sciences

Ghent University

IWASOM, July 16, 2013

ZnGa2S4 as a host for Eu2+-activated luminescence

Jonas Joos, Katleen Korthout, Philippe Smet, Dirk Poelman



SEM-CL-EDX



Monochromator CCD

Optical fiber

SE detector

BSE detector

EDX detector

Electron beam

Sample stage


Zn1-xEuxGa2S4

A1


SEM-CL-EDX



SE image

CL spectrum in each mapped point

elemental maps

Typ. 2

00

lines


Zn1-xEuxGa2S4

A1


X-ray diffraction



measurement

ZnGa2S4 (1 1 0)

EuGa2S4 (4 4 2)

EuGa2S4 (4 4 0)


Zn1-xEuxGa2S4

A2


X-ray diffraction



measurement fit

ZnGa2S4 (1 1 0)

EuGa2S4 (4 4 2)

EuGa2S4 (4 4 0)


Zn1-xEuxGa2S4

A2


X-ray diffraction



measurement fit

ZnGa2S4 (1 1 0)

EuGa2S4 (4 4 2)

EuGa2S4 (4 4 0)


Zn1-xEuxGa2S4

A2


X-ray diffraction



measurement fit


Zn1-xEuxGa2S4

A2





Zn1-xEuxGa2S4

A3




Dutch Belgian Beamline (BM26)


Zn1-xEuxGa2S4

A3



XANES @ ESRF Grenoble (FR) (Eu LIII edge)

Only divalent europium in powders


Zn0.96Eu0.04Ga2S4

Eu2O3 EuS

Zn1-xEuxGa2S4

A4




Eu2+ does not occupy Zn-site

Experimental result Simulation


Zn1-xEuxGa2S4

A5


Photoluminescence

Thermal stability (T0.5 = 475°C)

Quantum efficiency ( 71%)

Absence of emission saturation at high fluxes

Chemical stability


Sr1-xEuxGa2S4

A6