Traditional ligand-field theory has to be improved by taking into account both pure electronic contribution and electron-phonon interaction one (including lattice-vibrational relaxation energy).By means of improved ligand-field theory,the R line,t_2^(32)T_1 and t_2^(32)T_2 lines,t_2~2(~3T_1)e^4T_2,t_2~2(~3T_1)e^4T_1 and t_2e^2(~4A_2)~4T_1 bands,g factors of t_2~3 ~4A_2 and t_2^(32)E,four strain-induced level-splittings and R-line thermal shift of MgO:V^(2+) have been calculated.The results are in very good agreement with the experimental data.It is found that for MgO:V^(2+),the contributions due to electron- phonon interaction (EPI) come from the first-order term;the contributions from the second-order and higher terms are insignificant.In thermal shift of R line of MgO:V^(2+),the temperature-dependent contribution due to EPI is dominant. The results obtained in this work may be used in theoretical calculations of other effects of EPI.
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