Neighboring-Cation Substitution Tuning of Photoluminescence by Remote-Controlled Activator in Phosphor Lattice

Highly efficient red phosphors with superior intrinsic properties that are excited by ultraviolet or blue light-emitting diodes are important white light sources for our daily life. Nitride-based phosphors, such as Sr2Si3N8:Eu2+ and CaAlSiN3:Eu2+, are commonly more red-shifted in photoluminescence and have better thermal/chemical stability than oxides. Cation substitutions are usually performed to optimize photoluminescence and thermal quenching behavior. However, the underlying mechanisms are unclear in most cases. Here we show that neighboring-cation substitution systematically controls temperature-dependent photoluminescence behavior in CaAlSiN3:Eu2+ lattice. Trivalent cation substitution at the Ca2+ site degrades the photoluminescence in high-temperature environments but achieves better thermal stability when the substituted cation turns monovalent. The neighboring-cation control of lifetime decay is also observed. A remote control effect that guides Eu2+ activators in selective Ca2+ sites is proposed for neighboring-cation substitution while the compositional Si4+/Al3+ ratio adjusts to the valence of Mn+ (n = 1-3) cation. In the remote control effect, the Eu2+ activators are surrounded with nitride anions which neighbor with M3+-dominant and Si4+/Al3+-equivalent coordination when M is trivalent, but shift to the site where surrounded nitride anions neighbor with M+-dominant and Si-rich coordination when M is monovalent. This mechanism can efficiently tune optical properties, especially thermal stability, and could be general to luminescent materials, which are sensitive to valence variation in local environments.