Local structure and the electron paramagnetic resonance parameters for the Cr 3+ ions at K +-vacancy site in Cr 3+:KZnF 3 laser crystal

Abstract

The quantitative relationship between the electron paramagnetic resonance (EPR) parameters D, g ∥, g ⊥ and the local structure parameters of Cr 3+ ion in KZnF 3 crystals is established. The local structure for Cr 3+ paramagnetic center in KZnF 3:Cr 3+ crystal has been determined from EPR parameters of Cr 3+ ion. This work shows that the trigonal crystal field of Cr 3+ ion in KZnF 3 crystals comes from following two origins: (1) the nearest-neighbor K + vacancy caused by the charge compensation in the [1 1 1]-axis direction; and (2) the lattice distortions of the nearest-neighbor fluorine coordination caused by the K + vacancy and the differences in mass, charge, and radius between Cr 3+ ion and Zn 2+ ion. The unified calculation of the EPR zero-field splitting and g factors, taking into account the K + vacancy and the lattice distortions, has been carried out on the basis of the complete diagonalization procedure and the superposition crystal-field model, all calculation results are in excellent agreement with the experimental data. Although the main source of the trigonal crystal field comes from the K + vacancy caused by the charge compensation, the contribution of the lattice distortion cannot be neglected.