RESONANT RAMAN-SCATTERING AND PHOTOCHROMIC EFFECTS IN KI-MNO4-

A study is reported of photoinduced bleaching in the resonant Raman (R R) scattering spectra of KI:MnO4- crystals under laser excitation of t he MnO4- centers in resonance with the (1)A(1)-->T-1(2) optical transi tion, The bleaching effect is found to exist for all RR lines and is s tudied in detail as a function of time, temperature, and laser excitat ion power for the nu(1) line, A reversible and an irreversible process are observed, whose contributions to the total effect depend on tempe rature, It is established that the decrease in RR intensity is accompa nied by a decrease in integrated impurity absorption, The observed pho tochromic effects are attributed to photoinduced instability of the Mn O4- ions. The results find qualitative interpretation within a three-c enter model including the following photoelectronic processes: phototh ermal ionization of the permanganate, electron ejection from the excit ed state of the impurity center into the conduction band, and electron capture by traps of two types, with subsequent trap reactivation. The intensity distribution in a multiphonon RR scattering spectrum obtain ed at 5 K is used to find the main electron-phonon interaction constan ts, The introduction of the permanganate ion is found to excite a loca l lattice vibration, which is observed both near the exciting line and in combination with the fully symmetric intramolecular vibration of t he impurity ion itself. (C) 1997 American Institute of Physics.