Follow the charge: using advanced optical and X-ray spectroscopy to master charge transfer processes in phosphors

Abstract

Luminescent materials (also called phosphors) have the ability to emit light after energy is provided to the material. Typical applications include solid state lighting (e.g. LEDs), lasers and medical imaging. In some materials, impurities or imperfections in the crystal lattice can create defects (or traps) which extend the time between absorption and the emission of light. This is exploited in e.g. glow-in-the-dark safety signage and radiation dosimetry. Materials are usually optimized to obtain an as large as possible storage capacity, but due to insufficient knowledge about the trapping mechanism this is often done by a trial-and-error approach. In this joint FAPESP-FWO project, we will approach this issue from both an optical and structural point of view. At the University of São Paulo, we will investigate the formation of highly transparent persistent luminescence glass ceramics, as well as its optimization and characterization. At Ghent University, will occur the characterization of the optical signature of the charge carriers being caught at and released from the traps. Ultrafast spectroscopy is applied as a novel tool to probe also the dynamics of the intermediate steps in this process. To allow these measurements, they will use the prepared glasses, since it is required optically non-scattering samples. Based on the optical study, we expect to be able to steer the charge carriers to specific traps. This will finally allow a focused study of the structural properties of the traps using ultrafast X-ray absorption spectroscopy, at the Brazilian Sirius Synchrotron facility. The results of this project will allow the design of more efficient and highly customizable materials, which is done nowadays in a trial-and-error approach. (AU)