Infrared luminescence properties of Ni2+ in various chloride lattices: CsCdCl3, CsMgCl3, CdCl2, and MgCl2

A study of the infrared luminescence of Ni2+ (3A2g«3T2g: Oh notation) in four structurally related compounds is presented. Low temperature IR luminescence spectra are presented for the title compounds; energy assignments are given for the fine structure observed in the spectrum of Ni2+:MgCl2. Low temperature 3A2gå3T2g absorption spectra for Ni2+:CsCdCl3 and Ni2+:MgCl2 are shown; fine structure is observed mainly on the high-energy side of these bands. Temperature dependences of luminescence intensities and of luminescence decay rates are given; these dependences are described in terms of radiative and non-radiative models. Non-radiative decay is assumed to be through multi-phonon emission, and we use a single configuration coordinate (SCC) model. For each compound, the 'effective' phonon frequency of non-radiative decay is estimated to be approximately the mean frequency of the phonon spectrum. Variation in non-radiative behavior is well described in terms of the variation of the number of phonons involved and the Huang-Rhys parameter.