Dwight Swift and Dan Boye
Physics Dept., Davidson College
The Sol-Gel Process
 Synthesis at low temperatures
 Less exotic equipment required
 Accurate control of dopant concentrations
 Higher fluorescent ion capacity
 Control of other factors
 pH, distribution
 Many shapes possible
 Fibers, thin films
Sample Preparation
 Ingredients added as per recipe
 TMOS + DMF with catalytic acid
 Stages




Gelation – Long Si-O-Si chains condense into a gel
Aging – Chains cross-link and liquid precipitates out
Drying – Temperature is raised to remove excess liquid
Annealing – High temperatures (900C-1100C) densify glass
Fluorescence Quenching
 Energy transfer to the silica matrix
 Degree varies with host material
 Energy transfer to hydroxyl groups
 Water from re-hydration
 Cross-relaxation between Rare Earth (RE) ions
 Clustering on pore surfaces
 All optically non-radiative decay mechanisms
Energy Levels of
30
28
Emission Spectrum (λexc=240nm)
5D
3
26
5D 7F
3
J
22
Fluorescence (a.u.)
620nm
590nm
490nm
542nm
437nm
460nm
414nm
18
14
12
10
8
6
4
2
0
5D 7F
4
J
5D
4
20
378nm
Energy (1000cm-1)
24
16
3+
Tb
542nm
437nm
7F
0
1
2
3
4
5
7F
6
Wavelength (nm)
Sample Spectroscopy
 Nd:YAG pumped dye laser with summing crystals
 Excitation wavelengths
 Pulsed vs. Continuous excitation
 Allows a look at decay profile
 437 /542 peak amplitude ratio
 Focus on quenching mechanisms
 Calibrate across samples
Experimental Setup
Detector System
Laser System
KD*P
WEX
Pulsed
Nd:YAG
BS
532nm
Oscilloscope
Pin-hole
Filter
PMT
DCM
dye
laser
586nm
sol-gel
glass
monolith
1064nm
378nm
Filter
Spectrometer
Decay Profiles
Raw Data
Smoothed with
Savitzky-Golay Algorithm
542nm ~2mS
437nm ~400μS
Adding a DCCA
 Drying Control Chemical Additive (DCCA)
 N,N-dimethylformamide (DMF)
 Replaces H2O in the drying process
 Stronger bond
 Lower vapor pressure, capillary forces
 Reduced stress in drying
 Pore size uniformity
 Average pore size increase
 Densification to resist rehydration
Rehydration without DMF
0.6
Relative 5D3 to 5D4 ratio
0.5
0.4
0.3
0.2
0.1
0
0
5
Elapsed time (hours)
10
Rehydration with DMF
DMF-sol gel glass. 0.02%Tb, 1050C and 6h dwell.
0.45
5 D /5 D
3
4
Intensity Ratio
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
2
4
6
8
Elapsed Time [hours]
5 D /5 D
3
4
Intensity Ratio = constant= 0.409±0.001
10
12
0% Aluminum
0.08
0.07
437/542 Ratio
0.06
0.05
0.04
2.0% Tb
0.02% Tb
0.03
0.02
0.01
0
900
950
1000
1050
1100
Annealing Temperature (C)
1150
Aluminum Co-Doping
 Found to enhance fluorescence
 Somewhat ambiguous
 Brings in non-bridging Oxygens
 NBO’s sought out by Tb
 Originally thought to distribute Tb in matrix
 Effect of adding Al saturates at Al:RE ratios of 10:1 or
greater (without DCCA)
0.02% Terbium
3
437/542 Ratio
2.5
2
2% Al
1.5
1% Al
0% Al
1
0.5
0
900
950
1000
1050
Annealing Temperature (C)
1100
1150
0%Al
3
437/542 Ratio
2.5
2
0.02%Tb
0.05%Tb
1.5
0.2%Tb
0.5%Tb
1
1.0%Tb
2.0%Tb
0.5
0
850
900
950
1000
1050
1100
Annealing Temperature (C)
1150
1200
1%Al
3
437/542 Ratio
2.5
2
0.02%Tb
0.05%Tb
1.5
0.2%Tb
0.5%Tb
1
1.0%Tb
2.0%Tb
0.5
0
850
900
950
1000
1050
1100
Annealing Temperature (C)
1150
1200
2%Al
3
437/542 Ratio
2.5
2
0.02%Tb
0.05%Tb
1.5
0.2%Tb
0.5%Tb
1
1.0%Tb
2.0%Tb
0.5
0
850
900
950
1000
1050
1100
Annealing Temperature (C)
1150
1200
Summary
 DCCAs can help control quenching due to rehydration
 Addition of aluminum increases overall brightness
 Aluminum reduces cross relaxation
 Past work has shown that cross relaxation is
minimized for an Al:RE ratio of 10: 1 or greater
 With DMF, the 10: 1 ratio threshold appears to
decrease
 DMF binds more strongly than water to Tb
 Further study of this effect is needed
Future Work
 Look at Al:RE ratio reduction with DMF
 DMF Aluminum interaction
 Fluorescence with respect to DMF content
 Improve recipe for consistency
 Minimize sample cracking
Questions?