Mix 4.90 mL TMOS with 2.5 mL ethanol; stir for 10 minutes

1. 28 1D2 26 24 22 1G4 20 650nm 18 476nm 16 3F2,3 14 Energy (1000cm-1) 3H4 12 10 3H5 8 3F4 6 4 790nm 2 3H6 0 10%Zr/1% Nd 7.5%Zr/1% Er 10%Zr/1% Ho 1% Europium Glass Under UV light partial energy diagram for Eu3+ x103cm-1 25 5D3 5D2 20 5D1 2%Zr 12.5%Zr 20%Zr 30%Zr 5D0 15 Energy 10 1% Thulium Glass Mix 4.90 mL TMOS with 2.5 mL ethanol; stir for 10 minutes 5 partial energy diagram for Tm3+ 7F2 7F1 Often using two stir bars was helpful 0 7F0 partial energy diagram for Ho3+ Add 0.50 mL deionized H2Oand 20 µL conc. HCl; stir for 90 min x103cm-1 7.5%Zr 10%Zr 12.5%Zr 20%Zr 5G4 25 Add 2.5 mL ethanol simultaneously with… … Zr(OPr)4 via syringe, stir 10 minutes 3K8 20 5S2 Homogeneous sol Add solution of 1% RE ions dissolved in 2.5 mL H2O 5F5 15 Energy Reaction hydrolysis and condensation, ambient conditions, pH 1.5 to 3.5 Gelation polymeric gel forms “wet” gel 2 days, 40°C Aging solvents escape, pore contraction 1-3 days, 60°C • Drying • shrinkage, • densification, • pore collapse, • 2-4 days, 80°C 10 Stir 10 minutes or until all light precipitate has dissolved; cast into 12  75 mm tightly capped polypropylene test tubes 5 5I8 Karen Brewer Hamilton College Chemistry Ann Silversmith Hamilton College Physics Dan Boye Davidson College Physics Ken Krebs Franklin & Marshall College Physics Fluorescence of Rare Earth Ions in Binary Zirconia-Silica Sol-Gel GlassesJessica R. Callahan, Karen S. Brewer, Ann J. SilversmithDepartments of Chemistry and Physics Hamilton College, Clinton, NY spectroscopic results Pr Nd europium fluorescence introduction 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. 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. 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 sol-gel glass vs. melt glass 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 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 Er Eu sample quality • 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 • monitored at 612 nm • strongest excitation occurs at 393 nm corresponding to the 7F05D3 excitation • 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 why dope glasses with rare earth ions? 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 Applications of rare earth-doped materials2 • phosphors • solid state lasers • optical fibers • waveguides • antireflective coatings project goals 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) compare to our previous work in Al and Ti co-doped silica glasses1 challenges in doping sol-gel glasses with rare earth ions 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 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 • 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 • 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 • Tiresults show enhanced peak at 613 nm with longer exc indicating reduced energy migration and more uniform site distribution synthesis and processing partial energy diagram for Ho3+ enhanced fluorescence in thulium and holmium • 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 nm 663 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 co-doped • closely spaced energy levels prevents efficient luminescence • here, however, in glass annealed at 750 ˚C, we observe fairly strong fluorescence • 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 references (1) Boye, D.M.; Silversmith, A.J.; Nolen, J.; Rumney, L.; Shaye, D.; Smith, B.C.; Brewer, 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. Solids1998, 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. Solids1999, 259, 170. acknowledgements 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 our collaborators