Electron-lattice coupling parameters and oscillator strengths of cerium-doped lutetium oxyorthosilicate

Optical absorption of single-crystal, cerium-doped lutetium oxyorthosilicat e has been carefully measured in the temperature interval 10-300 K. Promine nt Gaussian absorption peaks occur at 3.432+/-0.002 eV (peak a), 3.502+/-0. 002 eV (peak b), 4.236+/-0.0002 eV (peak c), and 4.746+/-0.0002 eV (peak d) , in excellent agreement with previously reported excitation spectra. The s econd moments are well described by the usual linear model, yielding the Hu ang-Rhys parameter (S) and vibrational quantum energies for the individual peaks. All absorption bands are characterized by S>5 indicating strong coup ling between the Ce3+ ion and lattice. Temperature dependence of the band c entroids exhibits contrasting behavior that is dominated by higher-order co upling terms in the linear harmonic oscillator model or by crystal-field ef fects. Oscillator strengths of the 4f-->5d transitions are calculated from Smakula's formula and knowledge of the Ce3+ distribution between the two cr ystallographically inequivalent sites. Values for peaks b, c, and d range f rom approximately 0.003 to 0.004, and peak a spans magnitude approximately 0.012 to 0.018. From the known correlation between average Ce3+-ion-ligand distance and oscillator strength, we tentatively conclude that peak a is co rrelated with the seven-oxygen-coordinated site, and peaks b, c, and d are associated with the six-oxygen-coordinated site. These results support the previously proposed two-activation-center model and identify the centers as the two crystallographically inequivalent substitutional sites.