Defects in energy storage phosphors: friends or enemies?

First I will give a brief overview of the current activities in the LumiLab research group at Ghent University related to luminescent materials, highlighting cathodoluminescence spectroscopy in electron microscopy (SEM-CL) and the use of red-emitting Mn4+-doped fluoride phosphors for LED applications.

The main part will deal with a specific class of luminescent materials, namely phosphors which are able to store excitation energy in their lattice, in such a way that the time between excitation and emission can be extended up to minutes, hours or even many thousands of years. They find applications in geological dating and as x-ray storage phosphors (via optically stimulated luminescence), in persistent phosphors (via thermally driven release) or in mechanoluminescent phosphors (via pressure driven release).

Quite surprisingly, it is for many of those energy storing phosphor systems still largely unclear what the nature of the defect(s) responsible for the energy storage is. Often specific analytical techniques (such as XANES or EPR) or quantum mechanical calculations are required to probe their role. It is however commonly the case that those defects are playing a role which goes beyond the mere energy storage reservoir which we would like them to be. In this presentation, the focus will be on the different types of defects present in energy storage phosphors, and how they interact with each other, the luminescent centers and with the excitation light used to charge the phosphors.