Modelling of the slow emission decay of Pb²⁺, Tl⁺ centers

Abstract

The observed nonexponential decay of the slow luminescence componet of Pb²⁺ and Tl⁺ centres in alkali halide crystals has been modelled. The model is based on the assumption that there is lattice relaxation on the same time scale as the slow-component decay time. This relaxation is taken to be a response to the Jahn-Teller local distortion of the Tl⁺ and Pb²⁺ luminescence centres. We successfully fit experimental data for the slow componet decay of KX:Pb²⁺ and KX:Tl⁺ (X = Cl, Br, I). An essential feature of the model is that the lattice relaxation causes a time-dependent coupling of the Jahn-Teller levels and it is found that the coupling strength systematically increases as the anion size increases.

Key Words:

• Luminescence
• Jahn-Teller effect
• Alkali halides