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1. Transient and persistent spectral hole burning in Eu3+ -doped sol-gel produced SiO2 glass Transient and Persistent Holes D. M. Boye1, T. S. Valdes1, J. H. Nolen1 , A.J. Silversmith2, K.S. Brewer2, R. E. Anderman2 and R. S. Meltzer3 1Davidson College, Davidson, NC 28036 USA 2 Hamilton College, Clinton, NY 13323 USA 3University of Georgia, Athens, GA 30602 USA Type of hole burning depends strongly on the final annealing temperature and weakly on the organosilicate precursor. Silicon Transient and Persistent Hole Profiles Oxygen Al - network modifier T = 1.65K l=578nm Europium 800 TMOS Abstract Transient Holes Tann 800°C PSHB only P and T SHB 900°C P and T SHB P and T SHB 1000°C P and T SHB TSHB only TEOS TMOS Transient and persistent spectral hole burning (TSHB and PSHB) experiments were performed on Eu3+ ions in sol-gel SiO2 glasses with aluminum co-doping. Differences in the hole burning behavior were observed among samples made from two organosilicate precursors that were annealed to a series of final temperatures. All glasses exhibited persistent spectral holes when annealed to 800C but, as the annealing temperature was raised to 1000C, an increasing number of Eu3+ ions exhibited TSHB with a corresponding decrease in the number showing PSHB behavior. This is consistent with a reduction in metastable configurations with an increased final annealing temperature. The TSHB behavior is similar to that observed for Eu3+-doped silicate melt glass. 75MHz 290MHz • As Tann is raised, the glass becomes denser. • There is less likelihood of photo-induced rearrangement. 900 TEOS Eu Local Environment Fluorescence 80MHz 7F05D0 excitation TEM Images for TEOS and TMOS sol-gel precursors All samples annealed to 900°C Fluorescence (arb. units) 540MHz Persistent Holes TEOS Frequency [GHz] Transient Hole Behavior TMOS The average pore size in the TMOS samples is smaller and there is a narrower range of sizes than in the TEOS samples. Antihole position [MHz] Persistent Hole Behavior • Antihole position and hole width vary systematically across the 7F05D0 excitation line due to a linear variation in . • Transient hole width in sol-gel glasses shows weaker dependence on exthan the melt glass, indicating weaker crystal field coupling. This may be because the sol-gel glasses are not fully densified. Persistent Hole Profiles 10 sec Transient Hole Width [MHz] 30 sec Persistent Hole Width [MHz] 2 min 5 min Fluorescence 10 min Excitation Wavelength [nm] Hole burning time dependence • Constant fluence experiments show PSHB is 1-photon process. • Proposed mechanisms for PSHB: • Photo-induced rearrangement of local environment • Photoionization of Eu3+ • Photo-reduction of Eu3+ to Eu2+ T=1.7K l=578nm 800 TEOS Excitation Wavelength [nm] Hole recovery time dependence • Fluorescence level decreases in time as the hole is burned. The long tail is fit to an exponential with a time constant of 2.5s-1. • The fast component has a time constant 10x faster. a Frequency [GHz] 0.62e-2.5t % Hole Depth Ingredients: Er(NO3)3•6H2O Al(NO3)3•9H2O H2O (deionized) C3H6O HNO3 Tetraethylorthosilicate (TEOS) Titanium n-butoxide (TBOT) Experiment % Hole Depth Reaction - Hydrolysis and condensation - Room temp. - pH 1.5 to 3.5 Gelation - Polymeric gel forms - Supports stress elastically -”Wet” gel - 2 days, 40°C • Aging • - Solvent escapes • - Pore contraction • Shrinkage • 2 days, 60°C • Drying • - Shrinkage • - Cracking • - Densification • Pore collapse • 2 days, 90°C Fluorescence b 0.38e-24t Delay Time [ms] Time [s] • Both hole burning and recovery rates indicate: • Fast component – affects 1/3 of ions in first 100ms. • Slow component - ~10 times slower than fast component. Delay Time [s] Conclusions • Transient hole burning observed on Eu 3+ sol-gel produced glass for first time. • TSHB mechanism: redistribution of electron population among hyperfine levels. • Combination of PSHB and TSHB observed with the proportion of the two being strongly dependent on the final annealing temperature. • PSHB mechanism: photo-induced rearrangement of local environment. Regions at or near a pore boundary are ripe for metastable configurations having a range of barrier energies. Experimental Setup Cryostat with sample @ 77K Argon Laser Dye Laser Annealing Process References S.P. Feofilov, K.S. Hong, R.S. Meltzer, W. Jia and H. Liu, Phys. Rev. B60, 9406 (1999). T.T.Schmidt, R.M. Macfarlane, and S. Volker, Phys. Rev. B50, 15707 (1994). Acknowledgements AJS and DMB thank the NSF for a Research Opportunity Award associated with NSF DMR 9871864. Thanks to H.Y. Fang, currently of Sandia National Laboratories, for performing the TEM and x-ray diffraction work. Waveform Synthesizer Corresponding author: Dr. Dan Boye Physics Department Davidson College P.O. Box 7133 Davidson, NC 28035-7133 daboye@davidson.edu Ammeter Temperature (oC) PMT Computer with Labview software Monochromator Oscilloscope time (days)