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 Sr2Si5N8:Eu(2+) and CaAlSiN3:Eu(2+), 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:Eu(2+) lattice. Trivalent cation substitution at the Ca(2+) 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 Eu(2+) activators in selective Ca(2+) sites is proposed for neighboring-cation substitution while the compositional Si(4+)/Al(3+) ratio adjusts to the valence of M(n+) (n = 1-3) cation. In the remote control effect, the Eu(2+) activators are surrounded with nitride anions which neighbor with M(3+)-dominant and Si(4+)/Al(3+)-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.
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
Siao-Shan
SS
Wang
Wei-Ting
WT
Chen
Ye
Y
Li
Jing
J
Wang
Hwo-Shuenn
HS
Sheu
Ru-Shi
RS
Liu