One-Phonon Vibronic TransitionT2g3−A2g3ofNi2+in MgO

The near infrared emission of MgO: ${\mathrm{Ni}}^{2+}$ at 77 and 5 °K is reported. At helium temperature the spectrum consists of one sharp zero-phonon line between the ${\Gamma }_{3g}({}_{}{}^3{}_{}{}^{}T_{2g}^{}{}_{}{}^{},t_{2g}^5{e}_g^3)$ and ${\Gamma }_{5g}({}_{}{}^3{}_{}{}^{}A_{2g}^{}{}_{}{}^{},t_{2g}^6{e}_g^2)$ states, and an accompanying vibrational sideband. On the assumption that the perturbation giving rise to this sideband comes from an interaction of the impurity ion with its nearest neighbors, the intensity of the band can be described in terms of a weighted sum of localized Green's functions. A calculation of these functions is made based on a lattice-dynamical shell model. By taking a semiempirical admixture of the various calculated Green's functions, a good comparison with the one-phonon sideband is obtained. The agreement is shown to remain fair when using admixtures determined by considering a model where the ${\mathrm{Ni}}^{2+}$ ion experiences a varying electrostatic potential because of the motion of point-charge nearest neighbors.