Fluorescence of Rare Earth Ions in Binary Zirconia-Silica Sol-Gel Glasses
Jessica R. Callahan, Karen S. Brewer, Ann J. Silversmith
Departments of Chemistry and Physics
Hamilton College, Clinton, NY


optically clear were monoliths obtained
for zirconia content from 2% to 30%
some cracking can occur during drying
if water and solvent evaporated too
quickly
annealing above 750 ˚C can cause phase
separation of the zirconia, producing
opaque glassy materials
250
Synthesize glasses doped with Eu3+ and other rare earth cations
including erbium, neodymium, holmium, and thulium
Optimize processing parameters to obtain clear, crack-free glass
monoliths
Match concentrations of Zr with Ti glasses for direct
spectroscopic comparison
Increase the percentage of zirconium in the glass samples (up to
30% vs. SiO2)
Compare optical properties of the zirconia-silica glasses with
other sol-gel glasses (e.g., silica, titiania-silica, and chelated rare
earth dried gels)
10%Zr/1% Nd
7.5%Zr/1% Er 10%Zr/1% Ho
1% Europium Glass Under UV light
2%Zr
7.5%Zr 10%Zr
Add solution of 1% RE
ions dissolved in 2.5
mL H2O
Stir 10 minutes or until all light precipitate has
dissolved; cast into 12  75 mm tightly capped
polypropylene test tubes
1
2
4
5
1D
650nm
2-4 days, 80°C
Energy
2
5D
1
5D
0
10
7
5
590
610
630
7F
2
7F
1
7F
0
0
577nm
579.5 nm
579.5nm
573.2 nm
581nm
590
6
compare to our previous work in
Al and Ti co-doped silica glasses1
600
610
620
630
640
650
wavelength (nm)
 different spectral profiles when excitation l is
changed
 little energy migration between the different RE3+
sites in the glass
 shows declustering of the Eu3+ in the glass
 similar to results in Al co-doping
 Ti results show enhanced peak at 613 nm with
longer lexc indicating reduced energy migration
and more uniform site distribution
SiO2 glass no co-dopants
577nm
578nm
SiO2 glass Al3+ co-doped
579nm
575nm
575.1nm
SiO2 glass Ti4+ co-doped
581.6nm
600
610
620
2
1G
4
3F
2,3
3H
4
800
3H
5
3F
4
3H
6
Tm/Al glass 750ÞC x5
Tm/10%Zr, 750ÞC for 12 hrs
600
650
700
750
800
25
20
wavelength (nm)
 note that Tm/Al fluorescence spectrum is
multiplied by 5 in the above spectrum
 Zr co-doped glass fluoresces more efficiently
than Al co-doped & about the same as Ti codoped
x103cm-1
10% Zr, 12h dwell at 750 ÞC
excite 457 nm
520
570
640
partial energy
diagram for Ho3+
fluorescence of holmium-doped zirconia-silica
glass
comparison of Tm-doped glasses
476 nm exc
630
wavelength (nm)
enhanced fluorescence in thulium and holmium
790nm
1-3 days, 60°C
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
5D
D0 F1
fluorescence line narrowing results
Al co-dope
3
12.5%Zr 20%Zr
temperature program for zirconia-silica glasses
620
wavelength (nm)
670
 closely spaced energy levels prevents
efficient luminescence
 here, however, in glass annealed at 750 ˚C,
we observe fairly strong fluorescence
15
partial energy
diagram for Ho3+
5G
4
3K
8
5S
2
5F
5
10
5
5I
8
references
700
temperature (ÞC)
… Zr(OPr)4 via syringe,
stir 10 minutes
30%Zr
Drying
shrinkage,
densification,
pore collapse,
5
3
 fluorescence occurs from the 5D0 level in Eu3+
 sample excited in the charge-transfer region
 Al co-doped sample must be annealed at 1000˚C before significant fluorescence is observed
 Zr co-doped glass annealed only to 750 ˚C and gave comparable fluorescence
 in general, the Zr co-doped glasses fluoresce more brightly than Al co-doped & about the same
as Ti co-doped
 europium in zirconia-silica glass annealed at
750 ˚C has a longer decay time (~1.4 ms)
compared to aluminum co-doped silica glass
annealed to 1000 ˚C
 glasses without co-dopants have very short
lifetimes
476nm
2 days, 40°C
Aging
solvents escape,
pore contraction
Add 0.50 mL deionized H2O and 20 µL conc.
HCl; stir for 90 min
Add 2.5 mL ethanol
simultaneously with…
no co-dope
partial energy
diagram for Tm3+
Often using two stir bars was helpful
 dried gels heated from
ambient temperature to
750 ˚C over a period of
72 h
 heating rate = 1 ˚C/min
to preserve integrity of
sample
 dwell temperatures =
250 and 500 ˚C to
remove organics and
residual water/OH
groups
20%Zr
Energy (1000cm-1)
Mix 4.90 mL TMOS with 2.5 mL ethanol; stir
for 10 minutes
12.5%Zr
7
D0 F0
15
wavelength (nm)
1% Thulium Glass
synthesis and processing
Gelation
polymeric gel
forms
“wet” gel
5
time (ms)
Residual hydroxyl (OH) groups5
 present even after annealing to high temperatures
 give reduced fluorescence lifetimes through a non-radiative decay mechanism when close
to the rare earth cation in the glass
Reaction
hydrolysis
and
condensation,
ambient
conditions,
pH 1.5 to 3.5
25% Zr
570
25%Zr
0
Clustering of the rare earth cations in the glass4
 only a limited number of non-network oxygen atoms for the RE3+ to bond within the glass
 clusters formed through RE-O-RE bonding in the glass matrix
 energy migration is facilitated in the clusters
 fluorescence is quenched through a cross relaxation mechanism
Homogeneous sol
D07F2
comparison of fluorescence lifetimes
challenges in doping sol-gel glasses with rare earth ions
 addition of 1% RE3+ is the critical step
 high Zr amounts often gelled upon contact with
the RE3+(aq) solution
 after cast into tubes, sols were gelled at 40 ˚C
(24 h), 60 ˚C (24 h) and 80 ˚C (48 h) before
processing in furnace
550
 monitored at 612 nm
 strongest excitation occurs at 393 nm
corresponding to the 7F05D3 excitation
ln(fluorescence)
Applications of rare earth-doped materials2
 phosphors
 solid state lasers
 optical fibers
 waveguides
 antireflective coatings
450
5
wavelength (nm)
project goals
In the lanthanide series, the optically active electrons are shielded by
filled s and p shells producing
 narrow spectral lines
 long fluorescence lifetimes
 energy levels that are insensitive to the environment
350
2%Al 1%Eu
5D
550 nm
why dope glasses with rare earth ions?

exc 254nm, RT
20
fluorescence intensity (arbitrary units) 7F0→5D0
sample quality
Disadvantages3
 heating must be carefully & consistently controlled
 processing times can be long (> 2 weeks)
 cracking during aging, drying, or densification can be
extensive
 residual hydroxyl groups & RE clustering in samples quench
fluorescence
Synthetic obstacles
 rapid hydrolysis of the zirconium alkoxide precursor vs. that of TMOS
 precipitation of the zirconia as a opaque solid during synthesis
 choosing processing temperatures & programs to limit the precipitation
of zirconia during transformation from gel to glass
Eu
fluorescence (arb. units)
Er
excitation spectrum of Eu-doped zirconia-silica
glass
intensity (arbitrary units)
In this project, rare earth-doped zirconia-silica glasses have been
successfully produced through the co-hydrolysis of Zr(OiPr)4 with Si(OMe)4
in ethanol. Careful drying and aging of the gels produced clear, crack-free
glass monoliths. Optical properties were then studied via laser and
fluorescence spectroscopy.
25
emission spectrum comparing Eu-doped
glasses
fluorescence (arb. units)
Advantages3
 high purity starting materials & lower processing
temperatures
 higher concentrations of RE3+ possible
 simple manipulations & greater homogeneity of samples
 chemical composition can be varied & precisely controlled
 processing parameters can be readily changed & optimized
intensity (arbitrary units)
Our success in the synthesis of rare earth-doped TiO2-SiO2 glasses and their
spectroscopic results1 led us to re-examine our preliminary work on the
synthesis of the zirconium analogs.
QuickTi me™ and a TIFF (U ncompressed) decompressor are needed to see this picture.
663 nm
sol-gel glass vs. melt glass
x103cm-1
europium fluorescence
fluorescence (arb. units)
introduction
Nd
partial energy
diagram for Eu3+
Energy
Pr
spectroscopic results
600
500
400
300
200
100
0
0
1
2
time (days)
3
4
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K.S. J. Lumin. 2001, 94-95, 279.
Silversmith, A.J.; Boye, D.M.; Anderman, R.E.; Brewer, K.S. J. Lumin. 2001, 94-95,
275.
(2) Steckl, A.J.; Zavada, J.M., eds. MRS Bulletin, 1999, 24, 16-56.
Scheps, R. Prog. Quantum Electron. 1996, 20, 271.
Reisfeld, R. Opt. Mater. 2001, 16, 1.
Weber, M.J. J. Non-Cryst. Solids, 1990, 123, 208.
(3) Brinker, C.J.; Scherer, G.W. Sol-Gel Science: The Physics and Chemistry of Sol-Gel
Processing, Academic Press, Boston, 1990.
(4) Almeida, R.M. et al. J. Non-Cryst. Solids 1998, 232-234, 65.
Arai, K.; Namikawa, H.; Kumata, K.; Honda, T.; Ishii, Y.; Handa, T. J. Appl. Phys.
1986, 59, 3430.
(5) Lochhead, M.J.; Bray, K.L. Chem. Mater. 1995, 7, 572.
Stone, B.T.; Costa, V.C.; Bray, K.L. Chem. Mater. 1997, 9, 2592.
Nogami, M. J. Non-Cryst. Solids 1999, 259, 170.
acknowledgements
our collaborators
This work sponsored in part by the Research
Corporation through a Cottrell College
Science Award
JRC thanks the General Electric Fund at
Hamilton College for summer research
stipends
Karen Brewer
Hamilton College
Chemistry
Ann Silversmith
Hamilton College
Physics
Dan Boye
Davidson College
Physics
Ken Krebs
Franklin & Marshall College
Physics