The photoluminescence spectra of Ti3+-doped YAlO3, Y3Al5O12 and Al2O3 crystals display weak zero-phonon lines and broad vibronic side bands. The zero-phonon lines are due to the splitting of the 2T2g ground state into three Kramers' doublets by the combined effects of static axial crystal field, Jahn-Teller effect and spin-orbit interaction. A molecular orbital method is used to calculate the relative intensities and polarizations of both zero-phonon lines and broad band in terms of the mixing of odd-parity ligand wavefunctions into even-parity Ti3+ wavefunctions by odd-parity crystal fields of T1u and T2u symmetries at sites with tetragonal and trigonal symmetries. The odd-parity distortions may be static or dynamic and are of crucial relevance in determining the strength of vibronically induced transitions. In general, selection rules for optical spectra are uniquely determined by group theory. The relevance of the molecular orbit description of the d-d transitions is that it permits a physical interpretation of the strength of optical spectra in terms of the covalent charge transfer from ligand ions to central ions induced by odd-parity crystal field distortion.
|Number of pages||10|
|Journal||Applied Physics B Photophysics and Laser Chemistry|
|Publication status||Published - 1 Feb 1991|
- emission spectra
- photoluminescence spectra
- crystal field distortion