Energy Spectra, g Factors and Their Pressure-Induced and/or Thermal Shifts of SrTiO3:Cr3+ and SrTiO3:Mn4+ IV: R-Line Thermal Shifts of SrTiO3:Cr3+

Abstract

The local impurity-vibration modes (especially,the Iow-frequency one) of SrTiO3:Cr3+ cause a very large R-line blue-shift; while the Raman term, neighbor-level term and optical-branch term relevant to the lattice vibration cause smallred shifts. The algebraic sum of them gives rise to the observed unusual and large R-line thermal shift (blue-shift) of SrTiO3:Cr3+. By taking into account all the irreducible representations and their components in the electron-phonon interaction (EPI) as well as all the levels and the admixtures of basic wavefunctions within d3 electronic configuration, the values of the parameters in the expressions of thermal shift (TS) from EPI for the ground level, R level and R line of SrTiO3:Cr3+ have been evaluated; the R-line TS and various contributions to it have been calculated in two temperature ranges (30 K≤T≤80 K and 130 K≤T≤300 K). The contribution to R-line TS from thermal expansion has been approximately neglected in this work. Furthermore, the improvement on simplified approximation of adopting a single low-frequency impurity-mode and neglecting its hardening in low-temperature region has been made.