Optical and Electron-Spin-Resonance Studies of the ICl−VKCenter in KCl: I

Abstract

The I${\mathrm{Cl}}^{-}$ $V_K$ center, a $〈110〉$-oriented self-trapped hole center, has been investigated in x-irradiated KCl: I and KCl: I: Pb at low temperatures by optical and electron-spin-resonance techniques. Three optical transitions are identified at 430, 840, and 1000 nm by anisotropic absorption measurements; their observed $\sigma$ polarizations and relative intensities are consistent with a molecular-orbital model modified for $X{Y}^{-}$ molecule-ion centers. Pulse-annealing experiments monitored by ESR and correlated with thermoluminescence data and absorption spectrum changes give information on the formation and thermal stability of I${\mathrm{Cl}}^{-}$. An improved analysis of the ESR spectrum has been carried out, taking into account deviations from axial symmetry. Perturbation theory calculations are extended to include some terms to fourth order. The observed $\left|\Delta m\right|=1, 2$ forbidden transitions are fitted with these equations, allowing a determination of the sign, as well as the magnitude, of the large iodine quadrupole interaction.