Abstract
The dopant-host interactions were considered in the - and -doped cubic C-type rare-earth oxides as well as in nondoped and -doped yttrium gallium garnets The investigations were based mainly on the analyses of optical absorption and luminescence spectra using both new and previously published data. The concept of the crystal field (CF) strength parameter was used in the considerations. When a dopant different from the host cation is embedded into the host lattice, a decrease in the site symmetry, distortions, and/or stresses are usually introduced. These local effects were found to affect significantly the strength of the crystal field in both -doped and when compared to nondoped and With increasing positive size mismatch between the dopant and the host cation, the CF effect was found to be enhanced. The origin of this effect may be of electrostatic or covalent nature due to the decrease in dopant-oxygen distances or the delocalization of the electrons, respectively. High-pressure investigations on -doped support the present conclusions. The formation of neighbor pairs in doped garnets induces additional lines in the optical spectra. For large ions such as and in or the pair lines compared to isolated ions result from modifications in the CF effect due to local distortions. The superexchange interaction for near-neighbor and pairs is manifested in dynamical behavior.
- Received 15 March 2001
DOI:https://doi.org/10.1103/PhysRevB.64.195108
©2001 American Physical Society