TEMPERATURE-DEPENDENCE OF PHONON-ASSISTED EXCITATION PROBABILITY IN GDTB(MOO4)(3) - EVIDENCE FOR A CHANGE IN ELECTRON-LATTICE COUPLING NEARA STRUCTURAL PHASE-TRANSITION

Temperature dependence of the intensity of the phonon-assisted excitat ion probability (as a function of the intensity of the luminescence ba nds corresponding to the D-5(4)-->F-7(J) transitions) of Tb3+ ion in G dTb(MoO4)(3) (GTMO), above and below the ferroelectric phase transitio n temperature (T-c) is investigated in the present work. The experimen ts reveal a sharp change in the intensity near T-c. This change is att ributed to a sharp change in the electron-phonon coupling near T-c. A phenomenological model is proposed to fit the experimental data, in br oad accordance with the Ginzburg-Landau equations for critical behavio r. The investigations also clearly indicate that phonon-assisted excit ation probability can be used to probe structural phase transitions.