EPR and optical spectra of Ni²⁺-V_Ag in silver chloride and silver bromide

Abstract

The optical absorption and EPR spectra of Ni²⁺-V_Ag centres in the AgCl:Ni²⁺ and AgBr:Ni²⁺ systems have been investigated theoretically on the basis of the complete energy matrices including the electron–electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (V_Ag) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to V_Ag is shorter than others for both AgCl:Ni²⁺ and AgBr:Ni²⁺ systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX₆)⁴⁻ clusters in AgCl and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni²⁺ ion has a smaller ionic radius and more effective charge than the Ag⁺ ion.

Keywords:

• local lattice structure
• complete energy matrices
• EPR and optical spectra

Acknowledgements

This work was supported by the Doctoral Education Fund of Education Ministry of China (No. 20050610011) and the National Natural science Foundation of China (No. 10774103).