Enhanced luminescence intensity of CaSi₂O₂N₂: Eu²⁺ phosphor by using flux in the preparation process and incorporating Gd³⁺ ions

In this study, CaCl₂, NH₄Cl, and CaF₂ were selected as the flux respectively to assist the preparation of the yellow emitting phosphor of CaSi₂O₂N₂:Eu²⁺ by the solid-state reaction method. The influence of flux nature on the crystalline structure, morphology and photoluminescent behavior of the CaSi₂O₂N₂:Eu²⁺ was extensively investigated. Results proved that adding flux can significantly enhance the crystallinity and the emission intensity of the resultant powders. Pure and well crystallized CaSi₂O₂N₂:Eu²⁺ was formed by using CaCl₂ flux at a relatively low temperature (1250 °C) and gave much enhanced yellow emission intensity than that in other samples (around 1400 °C). Further increase of the emission intensity was achieved by the Gd³⁺ doping. The experimental results showed that the doping of a certain amount of Gd³⁺ can expand the lattice and improve the absorption and emission intensity of CaSi₂O₂N₂:Eu²⁺. When the Gd³⁺ content (x) increases up to 0.04 the luminescence intensity reaches maximum which is about 2 times as that of the phosphor without Gd³⁺ doping. A white light LED lamp using the optimal phosphor (Ca_0.89Eu_0.05Gd_0.04Si₂O₂N₂) had the color temperature of 5100 K with luminous efficiency of 41 lm W^-1 and color rendering index of Ra=76, indicating that Ca_0.89Gd_0.04Si₂O₂N₂:0.05Eu²⁺ is a good candidate yellow emitting down-conversion phosphor for white LEDs application.