Effects of the spin-triplet states mixture and electron-phonon coupling in Y₃Al₅O₁₂:Cr⁴⁺

¹ Fukui Institute for Fundamental Chemistry, Kyoto University, 34-4 Takano Nishihiraki-cho, Sakyo-ku, Kyoto 606-8103, Japan
² Department of Physics, West University of Timisoara, Bd. V. Parvan No. 4, 300223, Timisoara, Romania
³ Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan

Corresponding author: brik@fukui.kyoto-u.ac.jp

Received: 6 May 2004
Revised: 4 August 2004
Accepted: 18 October 2004
Published online: 21 December 2004

Abstract

The exchange charge model of the crystal field is applied to calculate the complete energy level scheme of the Cr⁴⁺ ions in Y₃Al₅O₁₂ using   symmetry at the Cr⁴⁺ position. Mixture of the spin-triplet states arising from the  and  terms of the 3d ²-electron configuration is shown to have a profound effect on the energy levels sequence. Large splittings of the orbital triplets originating from the “parent” T_d symmetry are explained by large contribution of the low-symmetry component of the crystal field. Huang-Rhys parameter and effective phonon energy are evaluated from the experimental spectroscopic data available in the literature. Temperature-dependent probability of the nonradiative transition between the ground and first excited states is drawn; the emission band shape is obtained using the single configuration coordinate model.