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: