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Energy transfer in Ce/Tb co-doped sol-gel silica
H.A.A. Seed Ahmed1,2, J.R. Botha3, W.D. Roos1, O.M. Ntwaeaborwa1 and R.E. Kroon1
1Department of Physics, University of the Free State, Bloemfontein 2Department of Physics, Faculty of Education, University of Khartoum, Sudan
3Department of Physics, Nelson Mandela Metropolitan University, Port Elizabeth
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outline
• Introduction
• Experimental
• Results
• Future work
• Conclusion
Page 3
introduction
Why energy transfer
• To develop the efficient of • Optical devices (laser – optical amplifer)
• Luminescence materials for particular applications (displays – lights)
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introduction
Why silica (SiO2)
• transparent to UV
• chemically stable
• non-hygroscopic
• amorphous
• higher dopant concentration
Page 5
introduction
Why sol-gel
• Produce high purity glass
• Low temperature (below the melting point)
• Allow higher dopant concentration than the melt process
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introduction
Why Ce
• Allowed optical transition 4f-5d
• Broad emission (high possibility to overlap with the absorption band of the acceptor)
5d1
4f1 2F7/2
2F5/2
2D5/2
2D3/2
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introduction
Why Tb
• Brightness green emission suitable for lighting and display devices
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introduction
D* + A D + A*
Sensitised photoluminescence and Förster-Dexter theory (thesis)
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introduction
Emission
Absorption
Emission
Absorption
http://www.invitrogen.com/site/us/en/home/support
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Experimental
SiOR
OR
OR
OR
OH2+ ROH+SiOH
OROR
OR
+ OH2Si
OROR
OH
OR
SiOH
OROR
OR
+ SiO
Si
OR OR
OR OR
OR OR
+ + ROHSiOR
OROR
OR
SiO
Si
OR OR
OR OR
OR OR
SiOH
OROR
OR
Hydrolysis
Condensation
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Oxygen Silicon
http://www.isolgel.com
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FTIR
PL (xenon lamp)
PL (He-Cd laser)
CL UV-vis
XPS
XRD
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Results
15 20 25 30 35 40 45 50 55 60 65 70
Room temperature
XRD of undoped
silica produced
using sol-gel method
6000C
Co
un
ts (
arb
. u
nits)
2 (deg)
10000C
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Results
4000 3000 2000 1000
0
20
40
60
80
100
1000oC
600oC
FTIR of pure silica
T
ran
sm
itta
nce [
%]
Wavenumber cm-1
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Results
400 500 600 700
Lu
min
escen
ce in
ten
sit
y (
a. u
.)
Wavelength (nm)
(4)
(3)
(2)
(1)
He-Cd laser
ex =325 nm
(1) pure SiO2
(2) SiO2:Ce
(3) SiO2:Tb
(4) SiO2:Ce,Tb
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Results
200 300 400 500 600 700
xenon lamp
(2)
exci. at (em)
= 545 nm emis. at (ex)
= 227 nm
Lu
min
escen
ce in
ten
sit
y (
a. u
.)
Wavelength (nm)
(1)
(1) SiO2:Tb
(2) SiO2:Ce,Tb
(2) at high PMT V
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Results
400 500 600 700
CL (2 kV, 10 A)
(1) SiO2:Ce
(2) pure SiO2
(2)
Lu
min
escen
ce in
ten
sit
y (
a. u
.)
Wavelength (nm)
(1)
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Results
400 500 600 700
PL
pure SiO2
SiO2:Ce
CL
pure SiO2
SiO2:Ce
Lu
min
escen
ce in
ten
sit
y (
a. u
.)
Wavelength (nm)
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Results
200 300 400 500 600 7000
10
20
30
40
50
60
70
80
90
100
SiO2:Ce
3+
wavelength (nm)
%R
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Results
920 910 900 890 880 870
3000
3100
3200
3300
3400
3500
3600
3700
c/s
Binding Energy (eV)
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Results Table 1. Fit parameter of the annealed sample.
ion 3d5/2/3d3/2 pos final state %area %total
Ce4+
v/u 882.3/901.0 Ce 3d94f2 O
2p4 36
80 v''/u'' 888.9/907.5 Ce 3d94f1 O
2p5 16
v'''/u''' 898.2/916.8 Ce 3d94f0 O
2p6 28
Ce3+
v0/u0 880.5/898.8 Ce 3d94f2 O
2p5 0
20
v'/u' 885.7/904.1 Ce 3d94f1 O
2p6 20
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Results
920 910 900 890 880 870
c/s
Binding Energy (eV)
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Results
200 300 400 500 600 70040
50
60
70
80
90
100
wavelength (nm)
%R
(re
du
ced
)
0
10
20
30
40
50
60
70
80
90
100
(2)
(1)
SiO2:Ce
3+
(1) reduced
(2) annealed
%R
(an
nea
led
)
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Results
200 300 400 500 600 700
xenon lamp
SiO2:Ce
exci. at (em)
= 460 nm
Lu
min
escen
ce in
ten
sit
y (
a. u
.)
Wavelength (nm)
emis. at (ex)
= 325 nm
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Results
200 300 400 500 600 700
(2) SiO2:Ce,Tb
emis. at
(ex)
= 325 nm
xenon lamp
(2)
exci. at (em)
= 545 nm
Lu
min
escen
ce in
ten
sit
y (
a. u
.)
Wavelength (nm)
(1)
(1) SiO2:Tb
emis. at
(ex) = 227 nm
200 300 400 500 600 700
xenon lamp
(2)
exci. at (em)
= 545 nm emis. at (ex)
= 227 nm
Lu
min
escen
ce in
ten
sit
y (
a. u
.)Wavelength (nm)
(1)
(1) SiO2:Tb
(2) SiO2:Ce,Tb
(2) at high PMT V
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Future work
• Vary the acceptor (Tb) concentration.
• Study the change on donor (Ce) lifetime by using suitable pulsed laser (ns) in order to suggest the mechanism response of the energy transfer.
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conclusion
• Ce/Tb co-doped silica successfully prepared by the sol-gel method.
• Very efficient energy transfer from Ce to Tb was detected after reducing processes.
• Sintering at 600oC was not sufficient either for reducing processes or to remove the water and hydroxyl ions from the prepared samples.