Eu2+ luminescence from 5 different crystallographic sites in a novel red phosphor, Ca15Si20O10N30:Eu2+

Abstract

Because it is impossible to realize broadband-type, red-light-emitting phosphors in the oxide composition pool, both pure nitrides and oxynitrides have been considered as potential red phosphors for use in light emitting diode (LED) applications. However, only a limited number of red phosphors have been discovered. For instance, only a few red phosphors such as CaAlSiN₃:Eu²⁺, Sr₂Si₅N₈:Eu²⁺, and their variations are worthy of notice. We examined the CaO–Si₃N₄ binary system to discover novel oxynitride red phosphors. We finally identified a novel oxynitride phosphor, Ca₁₅Si₂₀O₁₀N₃₀:Eu²⁺, with a cubic structure in the Pa space group. This phosphor showed a broadband-type, red-light emission at UV and blue-light excitations. A continuous-wave-excited, steady-state photoluminescence (PL) and a pulsed-laser-excited, time-resolved PL for the discovered phosphor were investigated in conjunction with a structural analysis of Ca₁₅Si₂₀O₁₀N₃₀:Eu²⁺. The variation in decay rate with respect to the detection wavelength was examined in detail, and the energy transfer among activators located at 5 different crystallographic sites proved to be responsible.