Post on 14-Jan-2016
description
Mechanisms of fluorescence enhancement in rare earth sol-gel
glass containing Al3+
A.J. SilversmithA. P. BeylerK.E. ArpinoN.T.T. Nguyen
Hamilton College
Davidson College
Whitman College
D. M. Boye
K. R. Hoffman
Mechanisms of fluorescence enhancement in rare earth sol-gel
glass containing Al3+
A.J. SilversmithA. P. BeylerK.E. ArpinoN.T.T. Nguyen
Hamilton College
Davidson College
Whitman College
D. M. Boye
K. R. Hoffman
Sol-gel glass materials
SynthesisWater + TMOSRE3+ and Al3+ saltsAcid catalyst
PropertiesOptically clear monolithsDensity ~1.7g/cm3 (compared to 2.2g/cm3 for vitreous silica)Porous
gel drying………..dry
annealed
SiCH3
CH3
H3CH3C
RE’s in sol-gel silicate glass
• Dopant concentrations up to 5% • Low fluorescence yield
• Today’s talkIncreased fluorescence yields with aluminum co-doping
• RE3+ associates preferentially with Al3+
• Local structure and vibrational energies altered• Local symmetry depends on Al content • Weaker coupling to host
Probe #1: Tb3+
• 5D3 sensitive to Al3+ content• 5D4 intensity unaffected
Ene
rgy
(100
0cm
-1)
414n
m
7F6
5
4
3
7F012
5D4
5D3
436n
m46
0nm
490n
m54
5nm
590n
m
620n
m
0
10
20
400 450 500 550 600 650
wavelength/nm
fluorescence/arb. unit
5D3 7FJ5D4 7FJ
0.02% Tb
4f84f75d
0.02% Tbexc=250nm
400 450 500 550 600 650
wavelength/nm
fluorescence/arb. unit
1% Al0.02% Alno Al
RE3+ associates preferentially with Al3+
Effect of Al saturates above 10:1 Al:RE ratio
supports J. Lægsgaard, Phys. Rev. B, 65 (2002), 17411
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 2 3 4
% Al
5D
3:5
D4 r
atio
0.02% Tb
Al:Tb is 10:1
Probe #2:Eu3+E
nerg
y (1
000c
m-1)
7F0
1
2
5D0
620n
m
0
10
2059
0nm
578n
m
CT band
550 570 590 610 630 650
wavelength (nm)
fluo
resc
ence 5D07F0
5D07F1
5D07F2
5D07F1 is magnetic dipole allowed
Local structure and vibrational energies altered
1.1
1.3
1.5
1.7
1.9
2.1
0 1 2 3 4% Al
lifetime/ms5D07F2
0.1% Eu900oC, 6hr
0
0.1%Eu
0 10 20 30 40
Al:Eu ratio
5 D0-
7 F0
Fully solvated RE returns to higher symmetry
550 570 590 610 630 650wavelength (nm)
fluorescence (arb units)
no Al1% Al
0.1%Euexc=250nm Low Al
concentration lowers local RE site symmetry…..
no Al4% Al
0.1%Eu samples
420 470 520 570 620
0Al
0.1Al
0.5Al
1Al
2Al
4Al
Wavelength (nm)
Flu
ores
cenc
e (a
rb u
nits
)
Blue emission in samples with Al
exc = 250nm
0.1%Eu
0 10 20 30 40
Al:Eu ratio
5 D0-
7 F0 ~578nm
~440nm
0
5
10
15
20
0 1 2 3 4
%Al
intensity of 4f-5d
exc
Tb excitation, monitor 542nm
200 250 300 350 400
no Al.02%Al0.1%Al0.2%Al0.50%1%2%3%
wavelength (nm)
542
nm
em
issi
on
4f84f75d
transitions within 4f8
weaker coupling to host with Al co-dopant
PAI(Post Annealing Immersion)
RE dopant near pore surface
RE dopant in densified material
K.E. Arpino et al. DPC2010 poster.
0
1
2
3
4
5
6
7
200 250 300 350 400
542n
m T
b3+ e
mis
sion
wavelength (nm)
no Al
1% Al
no Gd
Gd3+ absorptions
Low Al:RE ratio: site-symmetry is lowered. More admixture of opposite parity wavefunctions and increased transition probabilities.
High Al:RE ratio: highest frequency phonons of lower energy. Nonradiative decay rates are reduced.
Clues from Europium study:
Clues from Terbium study:RE ions associate preferentially with Al.
Al decreases the coupling between RE electrons and host.
Al may modify the location of RE dopants relative to pore surfaces.
Conclusions
Thank you:
DPC organizers
NSF-MRI Grant #0959552Hamilton College
Supported by: