Oscillator strengths, Huang-Rhys parameters, and vibrational quantum energies of cerium-doped gadolinium oxyorthosilicate

Temperature-dependent optical absorption of cerium-doped gadolinium oxyorth osilicate (Gd2SiO5:Ce) has been measured and analyzed for impurity-ion-latt ice coupling parameters and oscillator strengths. Although the spectrum con sists of overlapping Ce3+ bands and Gd3+ lines, two well-resolved Ce3+ band s with 10 K maxima at 3.32 eV (peak a) and 3.61 eV (peak b) are amenable to spectral analysis. These bands, previously assigned to Ce3+ ions occupying crystallographically inequivalent substitutional sites, are characterized by Gaussian line shapes and temperature-dependent half widths that are well described by the linear model of impurity-ion-lattice coupling. Huang-Rhys [Proc. R. Soc. A 204, 404 (1950)] parameters of peaks a and b are 22.7 and 5.7, respectively, indicating strong ion-lattice coupling, with vibrationa l frequencies 1.83x10(13) s(-1) (peak a) and 5.07x10(13) s(-1) (peak b). Pe ak b centroid is approximately temperature independent, but peak a centroid shifts to higher energy with increasing temperature. This dependence is ad equately described by including higher-order coupling terms in the ion-latt ice interaction, although crystal-field contributions cannot be excluded. A bsorption band oscillator strengths, f, are calculated from Smakula's [Z. P hys. 59, 603 (1930)] formula and knowledge of cerium concentration for the two inequivalent sites. In the interval 10-300 K, peak a f values range fro m (9.8 to 26.8)x10(-4) and peak b f values vary from (7.8 to 5.8)x10(-3). F rom the known correlation between oscillator strength and metal-ion-ligand separation, we identify peaks a and b as the seven- and nine-oxygen-coordin ated sites, respectively. (C) 2000 American Institute of Physics. [S0021-89 79(00)02011-9].