Effective local concentration of Tb3 in solgel silicate glasses

1
Effective local concentration of Tb3 in sol-gel
silicate glasses

• Carlos P. Ortiz
• Physics Department
• Davidson College

• Supported by
• NSF through MRI program
• ACS through PRF

2
Energy Levels in Terbium
Emission Spectrum (?exc240nm)
3
Experimental Setup
Detector
Laser System
oscilloscope
Pulsed NdYAG
Sample
Mirror
Frequency doubled with KDP
KDP summing crystal
PMT
Spectrometer
4 lens
Filter
Pin-hole
586nm
BS
532nm
12 lens
DCM dye laser
1064nm
3 lens
378nm
1068nm
Filter (blocks 378nm)
Mirror
4
Sample Data
5
Cross-Relaxation
5D3
5D4
Energy (1000cm-1)
7F0
1 2 3 4 5
7F6
Tb3 ion 1
nearby Tb3 ion 2
6
Cross-Relaxation
5D3

• In rare earths, dipole-dipole interactions
  dominate the process.
• The cross-relaxation rate depends strongly on
  the average distance between Tb ions, which
  motivates our investigation of the local ion
  concentration in our material.

5D4
Energy (1000cm-1)
7F0
1 2 3 4 5
7F6
Tb3 ion 1
nearby Tb3 ion 2
7
Inokuti-Hirayama Model
Where, fluorescence lifetime in absence of
cross-relaxation (single ions), the
effective local concentration of the ions, from
the perspective of the emitting ions, the
concentration at which the rate of
cross-relaxation equals the rate of radiative
emission, a integration constant G(1/2)
8
Graphical Analysis
Plot vs.
9
Graphical Analysis
Excite at 378nm Detect at 437nm
10
Single Fit
Excite at 378nm Detect at 437nm
11
Applying the IH model to sol gel glasses

• Take-home message
• There exist measurable optical differences in the
  fluorescence of Tb3 in a sol-gel glass host
  versus a crystal host.
• We have to take into account the effects of
  disorder in the material!

12
Assumptions

• Sol Gel
• Dopants non-uniformly spread throughout material
  clustered on specific regions.
• How?

• Crystal
• Dopants uniformly substitute for cations in the
  crystal lattice.
• How?

Fractal dimension!
13
Sol-Gel Inokuti-Hirayama Model
Where, fluorescence lifetime in absence of
cross-relaxation (single ions), the
effective local concentration of the ions, from
the perspective of the emitting ions, the
concentration at which the rate of
cross-relaxation equals the rate of radiative
emission, a integration constant
14
How is ß related to d?
Power dependence of cross-relaxation
Fractal dimension
15
Finding the fractal dimension
16
Finding t Lightly doped sample
t (1.10.1) ms
17
Graphical Analysis
Excite at 378nm Detect at 437nm
18
Effective Local Concentrations
Ideal Red Line - Uniform Distribution
19
Effective Local Concentrations
20
Effective Local Concentrations
21
Energy Levels in Tb3 and Gd3
6P7/2
5D3
Exciting nowhere near lowest level in Gd3
5D4
Energy (1000cm-1)
378nm
436nm
414nm
460nm
545nm
620nm
490nm
590nm
7F0
1 2 3 4 5
8S
7F6
22
(No Transcript)
23
Effect of Gadolinium co-doping
24
Effect of Aluminum co-doping
25
Effective Local Concentrations
26
Effect of Aluminum co-doping
27
Effect of Aluminum co-doping
At high Al concentrations, dopant distribution
changes
Varying Al from 0 to 2 has no effect on local
concentrations
28
Conclusions

• The distribution of Tb ions in sol-gel glasses is
  non-uniform.
• Gadolinium co-doping dilutes Tb clusters, which
  promotes emission from concentrated clusters.
• Aluminum co-doping does something other than
  dispersing tightly bound clusters.