Photoluminescence study on polar nanoregions and structural variations in Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystals

We report polar nanostructure and electronic transitions in relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PMN-PT) single crystals around morphotropic phase boundary (MPB) region by variable-temperature (80-800 K) photoluminescence (PL) spectra and low-wavenumber Raman scattering (LWRS). The discontinuous evolution from peak positions and intensity of luminescence emissions can be corresponding to formation of polar nanoclusters and phase transitions. Six emissions have been derived from PL spectra and show obvious characteristics near phase transition temperatures, which indicates that PL spectral measurement is promising in understanding the microcosmic mechanism. The Raman mode at 1145 cm^-1 indicates that temperature dependent luminescence phenomena can be modulated by thermal quenching.