Temperature Dependence of the Mn4+ R‐Lines and Vibronic Transitions in MgTiO3 and Mg2TiO4

The vibrational sidebands observed in the fluorescence spectrum of Mn4+ incorporated in magnesium titanates are studied. The salient features of the vibronic spectra are the existence of a resonant mode with a „hot line”︁ in MgTiO3:Mn4+ and the presence of very low energy vibrations in Mg2TiO4:Mn4+. The positions of the R1 fluorescence lines have been measured from 4.2 up to 250 °K. A significant thermal shift is observed and can be interpreted by the presence of linear and quadratic terms in the electron phonon interaction. An effective phonon distribution can be obtained from the vibronic sidebands. The vibrational energy of the lattice is calculated from this distribution and related to the thermal shift.