Exchange Interactions Between Chromium Ions in Ruby

Abstract

Twenty‐eight of the 100 or so sharp lines observed in relatively concentrated ruby (∼0.5%) are assigned to exchange‐coupled pairs of chromium ions in two different relative positions. It is shown that the splitting of the ⁴A₂ ground state of the Cr³⁺ ion is described by an isotropic exchange interaction in both cases, but that the splitting of the R levels (²E in an octahedral approximation to the crystal field) cannot be described so simply, probably because of the crystal field distortion due to the substitution of a Cr³⁺ ion for a nearby Al³⁺ ion. Values for the coupling parameters in the lower states are deduced, the criteria for the assignment discussed, and the pairs tentatively identified.