Materiales fotoactivos basados en Cu2+ y Mn4+ en condiciones extremas de alta presión y temperatura

Abstract

This work aims to investigate the structural and electronic properties of optically active transition-metal ions materials by optical spectroscopy as a function of pressure and temperature that have potential applications as catalysers, piezochromic sensors and giant dielectric ceramics -those based in Cu2+-, or as efficient red phosphors or white LED illumination or P-T sensors -those based on Mn4+ oxides. We study two Cu2+ compounds: Cs2CuCl4 and CaCu3Ti4O12. The focus in the copper chloride is to determine the optical properties dependent on the CuCl2-4 molecular units through the d-d transitions and Cl- to Cu2+ charge transfer bands. We also unravel the origin of its piezochromism, which is related with the shift of the charge transfer band gap with pressure. The titanium copper oxide is known for having a giant dielectric permittivity, here we investigate its electronic properties and crystal structure as a function of pressure. The interest of Mn4+ oxides lies in the potential of these materials to synthesise highly efficient red phosphors. We select two hosts, one with a perfect octahedral site for Mn4+ (Mg2TiO4) and another providing different low-symmetry sites for Mn4+ (Sr4Al14O25), so that we can investigate the influence of site symmetry on the photoluminescence properties and in particular, study their excited state dynamics. We have developed a dynamical model for explaining the uncorrelated variations of the photoluminescence lifetime and intensity variations of the Mn4+ phosphors with pressure and temperature.