Optical and electrical properties of RbI:Pb2+crystals

Abstract

The triplet splitting and the remarkable shape of the C band observed in RbI:Pb²⁺ are reported. By comparison with the splitting and shape of the C band theoretically calculated for a similar system by Toyozawa and Inoue it is found that a dynamical Jahn-Teller effect (DJTE) is the likely cause for the splitting, and that a weak interaction of A_1g and T_2g modes (of the PbI₆ molecular complex) before coupling to the excited state of the impurity ion is likely to be responsible for the observed shape. As the theory developed by Toyozawa and Inoue for the O_h symmetry of a monovalent impurity ion is in agreement with experimental results for this system with a divalent metal impurity Pb²⁺, the charge-compensating cationic vacancy does not seem to be changing the site of the impurity ion very much from O_h symmetry. Variation in electrical conductivity of these crystals with temperature showed that the conductivity is predominantly ionic. From the usual log sigma T against 1/T plot the defect parameters, such as the formation energy of a Schottky pair, the migration energy of the vacancy and the association energy of an impurity-vacancy pair are estimated to be 1.85, 0.49 and 0.55 eV respectively, which are in agreement with the theoretically estimated values published in earlier literature.