1. Fluorescence of Rare Earth Ions in Binary Zirconia-Silica Sol-Gel Glasses 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 Mix 4.90 mL TMOS with 2.5 mL ethanol; stir for 10 minutes Add 0.50 mL deionized H 2 O and 20 µL conc. HCl; stir for 90 min Stir 10 minutes or until all light precipitate has dissolved; cast into 12  75 mm tightly capped polypropylene test tubes Add solution of 1% RE ions dissolved in 2.5 mL H 2 O … Zr(OPr) 4 via syringe, stir 10 minutes Add 2.5 mL ethanol simultaneously with… Often using two stir bars was helpful 5D05D0 partial energy diagram for Eu 3+ 0 5 10 15 20 25 x10 3 cm -1 Energy 7F07F0 7F27F2 7F17F1 5D15D1 5D25D2 5D35D3 synthesis and processing 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 spectroscopic results references 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 sol-gel glass vs. melt glass Advantages 3  high purity starting materials & lower processing temperatures  higher concentrations of RE 3+ possible  simple manipulations & greater homogeneity of samples  chemical composition can be varied & precisely controlled  processing parameters can be readily changed & optimized Disadvantages 3  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 introduction Our success in the synthesis of rare earth-doped TiO 2 -SiO 2 glasses and their spectroscopic results 1 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(O i Pr) 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 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 materials 2  phosphors  solid state lasers  optical fibers  waveguides  antireflective coatings project goals Synthesize glasses doped with Eu 3+ 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. SiO 2 ) Compare optical properties of the zirconia-silica glasses with other sol-gel glasses (e.g., silica, titiania-silica, and chelated rare earth dried gels) challenges in doping sol-gel glasses with rare earth ions Clustering of the rare earth cations in the glass 4  only a limited number of non-network oxygen atoms for the RE 3+ 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) groups 5  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  fluorescence occurs from the 5 D 0 level in Eu 3+  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  different spectral profiles when excitation  is changed  little energy migration between the different RE 3+ sites in the glass  shows declustering of the Eu 3+ in the glass  similar to results in Al co-doping  Ti results show enhanced peak at 613 nm with longer exc indicating reduced energy migration and more uniform site distribution  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  monitored at 612 nm  strongest excitation occurs at 393 nm corresponding to the 7 F 0  5 D 3 excitation (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. 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. partial energy diagram for Ho 3+ 5 10 15 20 25 x10 3 cm -1 Energy 5I85I8 5F55F5 5G45G4 3K83K8 5S25S2 compare to our previous work in Al and Ti co-doped silica glasses 1  addition of 1% RE 3+ is the critical step  high Zr amounts often gelled upon contact with the RE 3+ (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  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 Homogeneous sol 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 europium fluorescence enhanced fluorescence in thulium and holmium 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Energy (1000cm -1 ) 3H63H6 3F43F4 1G41G4 1D21D2 650nm 476nm 3H53H5 3H43H4 3 F 2,3 790nm partial energy diagram for Tm 3+ partial energy diagram for Ho 3+ Pr Nd ErEu 550 nm 663 nm our collaborators Ann Silversmith Hamilton College Physics Dan Boye Davidson College Physics Ken Krebs Franklin & Marshall College Physics Karen Brewer Hamilton College Chemistry 10%Zr/1% Ho7.5%Zr/1% Er10%Zr/1% Nd 1% Thulium Glass 7.5%Zr10%Zr12.5%Zr20%Zr 1% Europium Glass Under UV light 2%Zr12.5%Zr20%Zr30%Zr