Effect of the trigonal field and a uniaxial stress on the vibronic triplet states of (3d)n ions in α‐Al2O3

Abstract

The local strain around the cation is expressed in function of the ion displacements in the cluster. It is shown that this local strain is related to the applied uniaxial stress by “local elastic compliances” which can be different from the crystal elastic compliances. The strain Hamiltonian which represents the ion‐strain interaction is given for any direction of pressure. Experimental parameters are defined, allowing to interpret the effect of the uniaxial stress on the transition between the fundamental vibronic singlet and the three lower vibronic states originating from T₁ or T₂ states in cubic symmetry.