Proxies from Ab Initio Calculations for Screening Efficient Ce³⁺ Phosphor Hosts

Abstract

Efficient phosphor performance, meaning a high photoluminescence quantum yield (Φ), requires the Ce 3+ ion to be hosted in a rigid crystal structure. This is particularly important when the phosphor is operated at slightly elevated temperatures, as is becoming conventional in high brightness, phosphor-converted white solid-state light-emitting diodes. We find the Debye temperature (Θ D ) of the undoped host crystal structure, which is readily calculated using ab initio methods within the quasi-harmonic approximation, is a useful proxy for structural rigidity. Θ D is found here to correlate well with the experimentally measured Φ for a number of Ce 3+ phosphors. In addition to being rigid, the host lattice must possess a large enough band gap ( E g ) that the Ce 3+ 4f to 5d transition can occur without interference from a host energy channel. As a sorting diagram for efficient hosts with high Φ, we propose using E g of the host, also readily calculated with high reliability using hybrid functionals, as one of the axes and Θ D as the other. Such a diagram is used to group the phosphor hosts that we have tested so far. It is interesting to note that a large E g and high Θ D are often contraindicated, suggesting a challenge in the search for new host structures. While the strategy is applied here for oxides hosts with Ce 3+ as the activator ion, it is transferable to other classes of host compounds, and to Eu 2+ based phosphors as well.