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Cerium-doped lutetium oxyorthosilicate (LSO:Ce) is an excellent scintillator due to its fast decay time (approximately 40 ns), excellent brightness (> 3X bismuth germanate), and high density (7.4 gm/cm3). However, the luminescence process in this technologically important scintillator is not well understood. Elucidation of electronic traps and their role in scintillator afterglow is lacking and fundamental ion-lattice coupling parameters have not been established. From thermally stimulated luminescence and emission spectra data on several oxyorthosilicates we show the traps to be intrinsic and uniquely associated with the C2/c crystal structure. Temperature dependent optical absorption measurements reveal prominent Gaussian bands at 3.432 eV (peak a), 3.502 eV (peak b), 4.236 eV (peak c) and 4.746 eV (peak d). The second moments are well described by the usual linear coupling model yielding the Huang-Rhys parameter and vibrational quantum energies for each peak. Oscillator strengths of the 4f yields 5d transitions are calculated from Smakula's formula and knowledge of the cerium distribution between the two crystallographically inequivalent sites. From the known correlation between average Ce-ion- ligand distance and oscillator strength we conclude that peak a is correlated with the seven-oxygen-coordinated site, and peaks b, c and d are associated with the six-oxygen- coordinated site.
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