Energy transfer and charge transfer processes in luminescent materials

Abstract

Luminescent inorganic solid-state materials (referred to as phosphors) are widely used in a broad range of common and less common devices like TV and computer panels, fluorescent lamps and LEDs, lasers, detectors, etc., and the research in this field is in continuous evolution. The targets are important: energy saving, environmental protection, reduction of production costs, new application possibilities (in medical diagnostics, solar cell technology, etc.), and so on. The development of a new phosphor is an interdisciplinary work involving physical, chemical and materials science issues, and in which the knowledge of the involved processes constitutes a fundamental as well as a puzzling challenge. There are still many open scientific problems in fact, and some of them have been dealt with in the ambit of this thesis. A study has been carried out, concerning the effect of the host composition and of the synthesis procedure on the morphological and luminescence properties of Dy3+-doped yttrium phospho-vanadate white-emitting phosphors. The role of the sample morphology has been investigated also in the case of CaMoO4:Pr3+ , a material whose emission dynamics is strongly influenced by charge transfer states arising from the interactions between active ions and host components. The investigations on the effects of the charge transfer states on the luminescence behavior have then been extended to the interesting case of Bi3+ in Y(P,V)O4 , that has been successfully dealt with in the light of a recently proposed model. Starting from these results, the positive effect of bismuth co-doping on the emission properties of YPO4 activated with several rare earth ions has been carefully characterized, and a new model has been proposed in order to account for the observed results. The last part of the thesis reports on a research activity on the photoswitching of bis-spiropyran using upconverting rare earths-based nanoparticles irradiated by near-infrared light, in the perspective to develop a new system for medical diagnostics and drug delivery.