Abstract
Optical absorption of single-crystal, cerium-doped lutetium oxyorthosilicate has been carefully measured in the temperature interval 10–300 K. Prominent Gaussian absorption peaks occur at (peak a), (peak b), (peak c), and (peak d), in excellent agreement with previously reported excitation spectra. The second moments are well described by the usual linear model, yielding the Huang-Rhys parameter (S) and vibrational quantum energies for the individual peaks. All absorption bands are characterized by indicating strong coupling between the ion and lattice. Temperature dependence of the band centroids exhibits contrasting behavior that is dominated by higher-order coupling terms in the linear harmonic oscillator model or by crystal-field effects. Oscillator strengths of the transitions are calculated from Smakula’s formula and knowledge of the distribution between the two crystallographically inequivalent sites. Values for peaks b, c, and d range from approximately 0.003 to 0.004, and peak a spans magnitude approximately 0.012 to 0.018. From the known correlation between average -ion-ligand distance and oscillator strength, we tentatively 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. These results support the previously proposed two-activation-center model and identify the centers as the two crystallographically inequivalent substitutional sites.
- Received 8 October 1999
DOI:https://doi.org/10.1103/PhysRevB.61.11973
©2000 American Physical Society