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

Efficient phosphor performance, meaning a high photoluminescence quantum yield (Φ), requires the Ce3+ 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 (ΘD) 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. ΘD is found here to correlate well with the experimentally measured Φ for a number of Ce3+ phosphors. In addition to being rigid, the host lattice must possess a large enough band gap (Eg) that the Ce3+ 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 Eg of the host, also readily calculated with high reliability using hybrid functionals, as one of the axes and ΘD 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 Eg and high ΘD are often contraindicated, suggesting a challenge in the search for new host structures. While the strategy is applied here for oxides hosts with Ce3+ as the activator ion, it is transferable to other classes of host compounds, and to Eu2+ based phosphors as well.