MnO ₄ ^- and MnO ₄ ^{2 -} molecular centers in cubic lattice: near infrared luminescence and resonance Raman spectra

We report the first observation of the near-infrared luminescence in RbI crystals doped with the MnO ₄ ^{2 -} (manganate) and MnO ₄ ^- (permanganate) ions. NIR luminescence spectra of the MnO ₄ ^- and MnO ₄ ^{2 -} ions show similarity in both the spectral region (8500-11 000cm ^{- 1} ) and the appearance of well-resolved vibronic structure at 4K caused by the electron coupling with the bending (e) modes of the impurity ions. This fine structure is considered as a result of e e and t ₂ e Jahn-Teller effect in the ground and excited electronic states, respectively. MnO ₄ ^{2 -} NIR luminescence is attributed to the d-d ( ² T ₂ -> ² E) transition of a single d-electron of Mn ^{6 +} .. The origin of the luminescence in case of MnO ₄ ^- -doped iodides is connected with the transient Mn ^{6 +} state, which is generated by the illumination-induced charge transfer process. The possibility of thermal population of Mn d-orbitals in case of MnO ₄ ^- ion is also discussed.