Ultra-bright green-emitting phosphors with an internal quantum efficiency of over 90% for high-quality WLEDs

Abstract

There is an urgent need to develop phosphors with high quantum efficiencies (QEs) since white light-emitting diodes (WLEDs) have emerged as a new generation of illumination materials. Utilizing energy transfer to improve the absorption of activators and adjust the emission colors of samples is one effective strategy. Here, color-tunable phosphors of the form CaAl₄O₇:Ce,Tb were synthesized aiming at efficient energy transfer from Ce³⁺ to Tb³⁺. Since Tb³⁺ can be suitably sensitized by Ce³⁺, the co-doped phosphors can be effectively excited by near-ultraviolet (NUV) light. The internal QE of CaAl₄O₇:0.04Ce,0.04Tb under 350 nm excitation is as high as 92.55%, and the external QE is 71.02%. A WLED fabricated from BAM:Eu²⁺, CaAl₄O₇:0.04Ce,0.04Tb, and CaAlSiN₃:Eu²⁺ with a 365 nm LED chip exhibited a correlated color temperature (CCT) of 4706 K and a color rendering index (CRI, R_a) of 81.44. The energy transfer mechanism and thermal stability of the phosphor were also investigated. The results provide an effective approach for developing highly efficient green-emitting phosphors for NUV WLEDs.