Theoretical studies of the g factors and local structure for Cr 5+ within Cr 2O 3 nanocrystals embedded in silica glass matrix

Abstract

The g factors and local structure for Cr 5+ within Cr 2O 3 nanocrystals embedded in the silica glass matrix are theoretically studied from the perturbation formulas of the g factors for a 3d 1 ion in orthorhombically distorted tetrahedra. From the calculations, the impurity-ligand bond angle (polar angle) related to [0 0 1] axis in the impurity center is about 0.25° smaller than that (≈54.74°) of regular tetrahedra, and the Azimuthal angle related to [1 0 0] axis shows a slight deviation by about 0.28°. The local structure of this center can be described as an elongated oxygen tetrahedron associated with tiny orthorhombic distortion due to the Jahn–Teller effect. The theoretical g factors and the optical transitions based on the above local structure are in good agreement with the experimental data. Moreover, the previous assignments of the electron paramagnetic resonance (EPR) spectra and the optical transitions based on tetragonal (D 2d) approximation are also improved by considering the slight orthorhombic distortion.