Red-emission enhancement of the CaAlSiN3:Eu2+ phosphor by partial substitution for Ca3N2 by CaCO3 and excess calcium source addition

Abstract

The effects of different calcium sources and the non-stoichiometric calcium addition on the preparation and photoluminescence properties of the red-emitting nitride phosphor CaAlSiN₃:Eu²⁺ were studied. Better crystallinity, enhanced emission intensity, and improved photoluminescence thermal stability of the phosphors were obtained when 10% of the calcium source (Ca₃N₂) was substituted by CaCO₃. The partial substitution for Ca₃N₂ by CaCO₃ resulted in the formation of more transient liquid phases at high temperature, which suppressed the evaporation of Ca/Eu elements to some extent. In order to effectively compensate for the calcium deficiency, excess initial Ca source was added, resulting in a narrower emission band and faster decay rate. Furthermore, the as-synthesized CaAlSiN₃:Eu²⁺ was employed as a red-emitting component to fabricate the two-phosphor-converted white LEDs, which exhibited high color rendering index R_a of ∼98 and warm correlated color temperature of 3000 K, and the narrower emission band with 140% initial Ca content gave an increase of 15% in luminous efficiency.