Fluorescence Line Narrowing and Decay Dynamics in Sol-Gel Glasses Containing Eu 3+

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Fluorescence line narrowing and decay dynamics
3+
in sol-gel glasses containing Eu
A.J. Silversmitha, R.E. Andermana, J. McComba, K.S. Brewera, D.M. Boyeb
aPhysics
Department, Hamilton College, Clinton, NY 13323 USA
bPhysics Department, Davidson College, Davidson, NC 28036 USA
Fluorescence Line Narrowing in Co-Doped Sol-Gels
Fluorescence line narrowing and emission decay measurements on Eu3+ doped sol-gel glasses
have been used to investigate different local Eu3+ environments in binary SiO2-TiO2 glasses
compared with SiO2 glasses containing Al3+. In particular, clustering of rare earth ions and the
effects of annealing temperature on residual hydroxide concentration are studied. The line
narrowing and fluorescence decay experiments show that the local environment at the rare
earth site is different in the Ti glass than in the Al glass. The Al and Ti co-doped samples
show pronounced line-narrowing implying little energy migration among Eu3+ ions. The 5D07F fluorescence decays are faster in the Ti glasses.
J
Fluorescence intensity
Abstract
5D
0
Eu3+
No Co-doping
579.5 nm
573.2 nm
7F
2
7F
1
7F
0
Fluorescence intensity
5% Al
Co-doped Sol-gel Structures
No co-doping
• Emission spectrum independent of exc
Efficient energy migration among Eu3+ ions
in different sites.
575nm
577nm
578nm
579nm
Co-doping with Al3+
• Different spectral profiles observed
Different sites excited as exc changes with
little energy migration
• Enhanced peak at 613nm with longer exc
Co-doping with
• Enhanced peak at 613nm with longer exc
• Different spectral profiles observed
Reduced energy migration and more uniform
site distribution than Al3+
Silicon
Oxygen
Ti - network former
Europium
Silicon
Oxygen
Al - network modifier
Europium
7.5% Ti
Fluorescence intensity
Ti4+
575.1nm
581.6nm
600
610
620
630
640
wavelength (nm)
Co-Doped Sol-Gel Recipes
Si02 Glasses with Al3+ co-doping
- Dissolve EuCl3·6H2O and Al(NO3)3·9H2O in deionized water
- Add 20 L concentrated nitric acid and 4.00 mL or 2.71x10-2 mol TEOS
- Stir reaction mixture for about 30 minutes until a homogeneous sol is formed
Excitation Spectra
Fluorescence Decay
0
Fluorescence intensity
1 - Al:1000?C
Drying and Annealing
- Gel at 40 oC for 2 days in a dry bath
- Age at 60 oC for 48 hrs
- Raise temperature to 90 oC over a six hour period and hold for 48 hrs.
- Ramp temperature 1oC/min in air for final densification
- Hold temperatures at 250 oC, 500 oC and 750 oC for 24 hrs. each
- Cool samples to room temperature in closed furnace
2 - Ti: 900?C
12.5% TBOT 900C
0% Al 900C
5% TBOT 900C
5% Al 1000C
ln (fluorescence)
TiO2-SiO2 Glasses
- Dissolve TEOS in absolute ethanol by stirring for ten minutes
- Add deionized water and 1M HCL and stir for two hours
- Add TBOT and additional absolute ethanol simultaneously
- Add RECl3 ·6H2O dissolved in 9.40 mL of deionized water
7F -5D
0
0
3 - Al: 750?C
4 - Ti: 750?C
-1
1
-2
2
3
-3
4
565
570
575
580
585
590
-4
0
wavelength (nm)
2
3
Argon Laser
Dye Laser
High concentration of Ti broadens and blue-shifts excitation line
Conclusions
Ammeter
• Ti co-doping reduces clustering of Eu ions in sol gel glasses common in high RE
concentrations.
PMT
Computer with
DataLogger or Labview
software
• Local environments for Eu ions are more homogeneous in Ti glass than in Al glass.
Monochromator
Oscilloscope
• Understanding of faster decay times in glasses containing Ti compared to Al requires
further investigation.
Samples
none
5% Al
Mol %
1
1
Annealing Process
Max Tanneal
1000
1000°C
750°C
5% Al
1
1000°C
7.5% Ti
1
750°C
7.5% Ti
1
900°C
5% Ti
1
900°C
12% Ti
1
900°C
Temperature (oC)
Co-dopant
Eu3+
800
Corresponding author:
Dr. Ann Silversmith
Physics Department, Hamilton College
198 College Hill Rd. Clinton, NY 13323
[email protected]
600
400
200
0
0
2
4
time (days)
6
8
10
5
Decay times increase with annealing temperature
• This is possibly due to reduction in hydroxyl
content, densification of structure, or shortening
of Ti – O bonds.
Decay times faster in Ti glass
Cryostat with
sample @ 77K
4
t [ms]
Ti co-doping produces red-shifted and narrower excitation line
• Electron cloud expansion,due to the increased covalency of RE-O
bonding, reduces the Coulomb repulsion between electrons and
lowers the free ion energy levels.
• More uniform site distribution for the RE.
Experimental Setup
1
This work sponsored in part by the Research Corporation
through a Cottrell College Science Award.
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