A Unified Calculation of the Optical and EPR Spectral Data for the Trigonal Cr3+ Center in Cr3+-Doped α -RbAl(SO4)2· 12H2O Alum Crystal

Xiao-Wu Li a, Yang Meia,b, Cheng-Fu Wei a and Wen-Chen Zhengc aSchool of Physics and Electronic Engineering, Mianyang Normal University, Mianyang 621000, P.R. China bResearch Center of Computational Physics, Mianyang Normal University, Mianyang 621000, P.R. China cDepartment of Material Science, Sichuan University, Chengdu 610064, P.R. China

Received: June 22, 2015; In final form: February 22, 2016

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The optical band positions and the spin-Hamiltonian parameters (g factors g∥, g⊥, and zero-field splitting parameter D) of alum α -RbAl(SO4)2· 12H2O:Cr3+ are calculated by diagonalizing the 120× 120 complete energy matrix based on the two-spin-orbit-coupling-parameter model. The model takes into account not only the contributions due to the spin-orbit-coupling parameter of central dn ion in the conventional crystal field theory, but also those due to ligands via covalence effect. The calculation indicates that the fourteen observed spectral data (eleven optical band positions and three spin-Hamiltonian parameters) can be reasonably and uniformly explained with four adjustable parameters (the Racah parameters B, C, intrinsic parameter A̅4(R) in the superposition model, and the trigonal distortion angle β). The calculations also suggest that contrary to the previous findings, the trigonal distortion of Cr3+ (entering the Al3+ site in the host crystal) center in α -RbAl(SO4)2· 12H2O is induced mainly by the oxygen (or water) octahedron around the Cr3+ ion rather than the more distant neighbors.

DOI: 10.12693/APhysPolA.129.340 PACS numbers: 71.70.Ch, 76.30.Fc, 78.40.Ha, 78.55.Hx