Fluorescence line narrowing and decay dynamics 3+ in sol-gel glasses containing Eu A.J. Silversmitha, R.E. Andermana, J. McComba, K.S. Brewera, D.M. Boyeb aPhysics Department, Hamilton College, Clinton, NY 13323 USA bPhysics Department, Davidson College, Davidson, NC 28036 USA Fluorescence Line Narrowing in Co-Doped Sol-Gels Fluorescence line narrowing and emission decay measurements on Eu3+ doped sol-gel glasses have been used to investigate different local Eu3+ environments in binary SiO2-TiO2 glasses compared with SiO2 glasses containing Al3+. In particular, clustering of rare earth ions and the effects of annealing temperature on residual hydroxide concentration are studied. The line narrowing and fluorescence decay experiments show that the local environment at the rare earth site is different in the Ti glass than in the Al glass. The Al and Ti co-doped samples show pronounced line-narrowing implying little energy migration among Eu3+ ions. The 5D07F fluorescence decays are faster in the Ti glasses. J Fluorescence intensity Abstract 5D 0 Eu3+ No Co-doping 579.5 nm 573.2 nm 7F 2 7F 1 7F 0 Fluorescence intensity 5% Al Co-doped Sol-gel Structures No co-doping • Emission spectrum independent of exc Efficient energy migration among Eu3+ ions in different sites. 575nm 577nm 578nm 579nm Co-doping with Al3+ • Different spectral profiles observed Different sites excited as exc changes with little energy migration • Enhanced peak at 613nm with longer exc Co-doping with • Enhanced peak at 613nm with longer exc • Different spectral profiles observed Reduced energy migration and more uniform site distribution than Al3+ Silicon Oxygen Ti - network former Europium Silicon Oxygen Al - network modifier Europium 7.5% Ti Fluorescence intensity Ti4+ 575.1nm 581.6nm 600 610 620 630 640 wavelength (nm) Co-Doped Sol-Gel Recipes Si02 Glasses with Al3+ co-doping - Dissolve EuCl3·6H2O and Al(NO3)3·9H2O in deionized water - Add 20 L concentrated nitric acid and 4.00 mL or 2.71x10-2 mol TEOS - Stir reaction mixture for about 30 minutes until a homogeneous sol is formed Excitation Spectra Fluorescence Decay 0 Fluorescence intensity 1 - Al:1000?C Drying and Annealing - Gel at 40 oC for 2 days in a dry bath - Age at 60 oC for 48 hrs - Raise temperature to 90 oC over a six hour period and hold for 48 hrs. - Ramp temperature 1oC/min in air for final densification - Hold temperatures at 250 oC, 500 oC and 750 oC for 24 hrs. each - Cool samples to room temperature in closed furnace 2 - Ti: 900?C 12.5% TBOT 900C 0% Al 900C 5% TBOT 900C 5% Al 1000C ln (fluorescence) TiO2-SiO2 Glasses - Dissolve TEOS in absolute ethanol by stirring for ten minutes - Add deionized water and 1M HCL and stir for two hours - Add TBOT and additional absolute ethanol simultaneously - Add RECl3 ·6H2O dissolved in 9.40 mL of deionized water 7F -5D 0 0 3 - Al: 750?C 4 - Ti: 750?C -1 1 -2 2 3 -3 4 565 570 575 580 585 590 -4 0 wavelength (nm) 2 3 Argon Laser Dye Laser High concentration of Ti broadens and blue-shifts excitation line Conclusions Ammeter • Ti co-doping reduces clustering of Eu ions in sol gel glasses common in high RE concentrations. PMT Computer with DataLogger or Labview software • Local environments for Eu ions are more homogeneous in Ti glass than in Al glass. Monochromator Oscilloscope • Understanding of faster decay times in glasses containing Ti compared to Al requires further investigation. Samples none 5% Al Mol % 1 1 Annealing Process Max Tanneal 1000 1000°C 750°C 5% Al 1 1000°C 7.5% Ti 1 750°C 7.5% Ti 1 900°C 5% Ti 1 900°C 12% Ti 1 900°C Temperature (oC) Co-dopant Eu3+ 800 Corresponding author: Dr. Ann Silversmith Physics Department, Hamilton College 198 College Hill Rd. Clinton, NY 13323 [email protected] 600 400 200 0 0 2 4 time (days) 6 8 10 5 Decay times increase with annealing temperature • This is possibly due to reduction in hydroxyl content, densification of structure, or shortening of Ti – O bonds. Decay times faster in Ti glass Cryostat with sample @ 77K 4 t [ms] Ti co-doping produces red-shifted and narrower excitation line • Electron cloud expansion,due to the increased covalency of RE-O bonding, reduces the Coulomb repulsion between electrons and lowers the free ion energy levels. • More uniform site distribution for the RE. Experimental Setup 1 This work sponsored in part by the Research Corporation through a Cottrell College Science Award.