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Antihole position and hole width vary systematically across the 7 F 0  5 D 0 excitation line due to a linear variation in. Transient hole width in sol-gel.

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Presentation on theme: "Antihole position and hole width vary systematically across the 7 F 0  5 D 0 excitation line due to a linear variation in. Transient hole width in sol-gel."— Presentation transcript:

1 Antihole position and hole width vary systematically across the 7 F 0  5 D 0 excitation line due to a linear variation in. Transient hole width in sol-gel glasses shows weaker dependence on ex than the melt glass, indicating weaker crystal field coupling. This may be because the sol-gel glasses are not fully densified. Frequency [GHz] Fluorescence 10 sec 30 sec 2 min 5 min 10 min T=1.7K =578nm 800 TEOS Transient and persistent spectral hole burning in Eu 3+ -doped sol-gel produced SiO 2 glass D. M. Boye 1, T. S. Valdes 1, J. H. Nolen 1, A.J. Silversmith 2, K.S. Brewer 2, R. E. Anderman 2 and R. S. Meltzer 3 1 Davidson College, Davidson, NC USA 2 Hamilton College, Clinton, NY USA 3 University of Georgia, Athens, GA USA Transient and persistent spectral hole burning (TSHB and PSHB) experiments were performed on Eu 3+ ions in sol-gel SiO 2 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 Eu 3+ 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 Eu 3+ -doped silicate melt glass. Abstract Conclusions Corresponding author: Dr. Dan Boye Physics Department Davidson College P.O. Box 7133 Davidson, NC Eu Local Environment Experiment Ingredients: Er(NO 3 ) 36H 2 O Al(NO 3 ) 39H 2 O H 2 O (deionized) C 3 H 6 O HNO 3 Tetraethylorthosilicate (TEOS) Titanium n-butoxide (TBOT) 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 Annealing Process time (days) Temperature ( o C) Al - network modifier Silicon Oxygen Europium Excitation Wavelength [nm] Persistent Hole Width [MHz] Transient and Persistent Holes Persistent Hole Behavior Experimental Setup Argon Laser PMT Dye Laser Cryostat with 77K Monochromator Ammeter Oscilloscope Computer with Labview software Waveform Synthesizer TEOS TMOS TEM Images for TEOS and TMOS sol-gel precursors All samples annealed to 900°C Type of hole burning depends strongly on the final annealing temperature and weakly on the organosilicate precursor. TEOSTMOS T ann 800°CPSHB onlyP and T SHB 900°CP and T SHB P and T SHB 1000°CP and T SHB TSHB only As T ann is raised, the glass becomes denser. There is less likelihood of photo-induced rearrangement. Frequency [GHz] Fluorescence Transient Holes Persistent Holes 800 TMOS 900 TEOS 75MHz 80MHz 290MHz 540MHz T = 1.65K =578nm The average pore size in the TMOS samples is smaller and there is a narrower range of sizes than in the TEOS samples. Constant fluence experiments show PSHB is 1-photon process. Proposed mechanisms for PSHB: Photo-induced rearrangement of local environment x Photoionization of Eu 3+ x Photo-reduction of Eu 3+ to Eu 2+ Hole burning time dependence Delay Time [ms] % Hole Depth Delay Time [s] % Hole Depth Hole recovery time dependence Time [s] b a 0.62e -2.5t 0.38e -24t a)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. b)The fast component has a time constant 10x faster. Fluorescence 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, (1994). Acknowledgements AJS and DMB thank the NSF for a Research Opportunity Award associated with NSF DMR Thanks to H.Y. Fang, currently of Sandia National Laboratories, for performing the TEM and x-ray diffraction work. Fluorescence (arb. units) 7 F 0  5 D 0 excitation Transient Hole Behavior Excitation Wavelength [nm] Transient Hole Width [MHz] Antihole position [MHz] 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. 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. Persistent Hole Profiles Transient and Persistent Hole Profiles

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