Investigation of relationships between absorption band energies of Tl ⁺ and the crystalline environment

The relationships between sp energy levels (A, B and C bands) as well as charge transfer band (D band) of Tl⁺ center and the crystalline environment were systematically investigated for the first time by means of dielectric theory of chemical bond for complex crystals. It is found that the coordination number of the central ion, the bond volume polarizability, the fractional covalence of the chemical bond between the central ion and the nearest anion, and the presented charge of the nearest anion in the chemical bond are the major factors influencing the positions of A, B, C and D bands of Tl⁺. Our model has successfully built links between the E _A, E_B, E_C and E_D of Tl⁺ center and the environmental factor he. The results indicate that both the energies of sp levels and the charge transfer band of Tl⁺ decrease with the increase of he. he has a linear relationship with the sp energy levels, and an exponential relationship with the CT band. The calculated results using our model are in good agreement with the experimental data. The current model can serve as a predicting tool and be applied to assign and reassign the A, B, C and D band positions of Tl⁺.