Temperature variation of the luminescence spectra in crystals
The luminescence spectra in cubic mixed crystals (0.6<x<1) grown by MBE have been studied in an energy range of around 2 eV as a function of temperature between 4.2 and 300 K. The observed luminescence is related to intra-ion optical transitions between the 3d electronic levels of perturbed by a crystal field. The luminescence displays a non-monotonic temperature dependence with a minimum at about 50 K. The occurrence of the minimum depends on the Mn molar fraction only very weakly. The temperature variation of the luminescence transition results mainly from the effect of screening of the Coulomb repulsion force between d electrons and from variation of the crystal field potential due to thermal lattice dilation and electron - phonon interaction.