EPR and optical spectroscopy of MnO42- doped proper ferroelastic K3Na(CrO4)2:: local transition and Jahn-Teller effect

We report the study of the polarized optical absorption, the near-infrared luminescence and the luminescence excitation spectra of the proper ferroelastic K3Na(CrO4)(2) crystals doped with MnO42- ions. It is obtained from the luminescence and the d-d absorption spectra that the 3d(1) electronic ground (E-2) and excited (T-2(2)) states of MnO42- are split by the monoclinic crystal field of the host lattice at T < 230 K. The well-resolved vibronic progressions in the luminescence spectra are ascribed to a strong coupling with a MnO42- bending nu(2) = 335 cm(-1) mode. The spectral dependence of the linear polarization degree rho(omega) of the charge-tranfer absorption for E vertical bar vertical bar c and E vertical bar vertical bar b polarization reveals a clear periodic structure due to interaction of local electronic states with a nu(1) = 816 cm(-1) local mode. The first EPR spectrum of the Mn6+ paramagnetic center in the K3Na(CrO4)(2):MnO42- crystal is studied. The local transition due to a local configuration instability of vibronic origin at low temperature T <= 18 K is detected and identified. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.