Multiphonon vibronic transition T2g1-A2g3 of Ni2+ in MgO

Abstract

The Γ5g(T2g1,t2g5eg3)-Γ5g(A2g3,t2g6eg2) vibronic spectrum is recorded in absorption and emission-under x-ray excitation-at crystal temperatures of 77 and 5°K. The spectrum involves up to four phonon processes and a theoretical treatment of such a transition is presented. A possible explanation of the band is suggested and, by using imperfect-lattice Green's functions for the nearest-neighbor motion, it is constructed to give excellent agreement with experiment. The transition is forced (electric dipole) by one of the T1u vibrations of the nearest-neighbor complex. Additional Eg vibrations couple in the higher phonon processes which suggest the presence of a Jahn- Teller distortion in the T2g1 excited state. However, it has not been possible to establish the presence of such a Jahn- Teller distortion from any other experimental data. A similar calculation is undertaken for the two-phonon band of the Γ3g(T2g3,t2g5,eg3)-Γ5g(A2g3,t2g6eg2) transition of Ni2+ in MgO. Again there is an indication of a coupling to Eg vibrations in the two-phonon process. Show more