Prediction and assignment of site occupation and energy levels for Pb ions in crystal hosts

The environmental factor h_e of the host was calculated quantitatively in Pb²⁺-doped 23 compounds based on the dielectric theory of chemical bond for complex crystals. The relationship between the A band energy E_A of Pb²⁺ and the environmental factor h_e was intensively studied. The results indicate that E_A of Pb²⁺ decreases linearly with increasing of h_e. A linear model was proposed which allows us to correctly predict and assign the site occupations and the position of A band for Pb²⁺-doped compounds if the crystal structure and the refraction index were known. Applied to SrGa₂O₄:Pb²⁺, CaAl₂B₂O₇:Pb²⁺ and SrAl₂B₂O₇:Pb²⁺, the theoretical predictions are in very good agreement with the experimental data. In SrGa₂O₄:Pb²⁺, the excitation spectrum of Pb²⁺ from two different cation sites was identified: the higher energy band of A (265 nm) from the site of Sr2, and the lower ones (280 nm) from the site of Sr1.