Investigation of Blue Excitation Dependent Conversion Efficiency in Phosphors for High Luminance Applications: Part 2

This study is a continuation of work discussed earlier [1]. The efficiency of high luminance semiconductor pumped phosphor sources depends not only on efficient generation of primary radiation from the semiconductor (LEDs or laser diodes), but also strongly on the conversion material which is often pushed to optical and thermal limits. Such conversion materials are typically operating upon high excitation flux and thermal load and nearly always exhibit sublinear behavior in output at high incident fluxes, due to several reasons. We have separated contributions from thermal and non-thermal quenching mechanisms, and in particular investigated phosphor saturation, or excitation quenching, in the converted light output as a function of blue pump intensity. It is important to distinguish between the true loss mechanisms (for example via Auger-like or excited state absorption processes) and the reduction in converted output due to increased transparency for the pump light (e.g. activator ground state depletion). The behavior of measured conversion efficiency as a function of excitation intensity is discussed in the context of parameters like temperature, activator concentration and excited state lifetime or host lattice. An updated model describing the observed dependencies in different luminescent systems (e.g. Ce3+ and Eu2+ based) is reviewed. [1] M. Raukas, J. Avallon, J. Kelso, A. Lenef, 230 th ECS Fall Meeting (PRiME 2016), Honolulu, HI, Oct 2-7, 2016.