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

outline

• Introduction

• Experimental

• Results

• Future work

• Conclusion

introduction

Why energy transfer

• To develop the efficient of • Optical devices (laser – optical amplifer)

• Luminescence materials for particular applications (displays – lights)

introduction

Why silica (SiO2)

• transparent to UV

• chemically stable

• non-hygroscopic

• amorphous

• higher dopant concentration

introduction

Why sol-gel

• Produce high purity glass

• Low temperature (below the melting point)

• Allow higher dopant concentration than the melt process

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

introduction

Why Tb

• Brightness green emission suitable for lighting and display devices

introduction

D* + A D + A*

Sensitised photoluminescence and Förster-Dexter theory (thesis)

introduction

Emission

Absorption

Emission

Absorption

http://www.invitrogen.com/site/us/en/home/support

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

Oxygen Silicon

http://www.isolgel.com

FTIR

PL (xenon lamp)

PL (He-Cd laser)

CL UV-vis

XPS

XRD

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

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

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

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

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)

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)

Results

200 300 400 500 600 7000

10

20

30

40

50

60

70

80

90

100

SiO2:Ce

3+

wavelength (nm)

%R

Results

920 910 900 890 880 870

3000

3100

3200

3300

3400

3500

3600

3700

c/s

Binding Energy (eV)

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

Reducing process

Results

920 910 900 890 880 870

c/s

Binding Energy (eV)

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

)

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

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

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.

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.