Fourier transform IR spectroscopy of Co²⁺ excitations in KZn_1−xCo_xF₃

Abstract

From a temperature-dependent study of the IR absorption spectrum of crystals of cubic KZn_1−xCo_xF₃ (with 0 < x < 0.15) we have identified electronic and vibronic transitions associated with isolated clusters of Co²⁺ ions. Single-ion transitions within the ⁴T_1g(⁴F) ground term were found at 950 and 1045 cm⁻¹, respectively, together with higher-frequency vibronics, most of which could be assigned to combinations of these electronic transitions with transverse optic phonons. At higher Co²⁺ ion concentrations (e.g. x = 0.12) other absorption features were observed and these have been attributed to vibronics associated with pairs of Co²⁺ ions.