K2CaPO4F:Eu2+,RE3+ for pc-WLEDs: Cationic substitution inducing tunable emission and anti-thermal quenching

Abstract

Near-ultraviolet (n-UV) chip based phosphor-converted white light-emitting diode (pc-WLED) is proposed as one of the methods to realize full-spectral illumination with high color rendering index (CRI). Accordingly, it is crucial to explore n-UV excitable, efficient, and thermally stable phosphors. Here in, the redistribution of Eu2+ on different crystallographic sites (K and Ca) of K2CaPO4F was achieved by introducing Ce3+ and other optically inert rare earth (RE) ions (La3+, Y3+, and Lu3+). This cationic substitution resulted in the enhancement of blue emission, the weakening of red emission, and the appearance of white emission finally. The introduction of RE3+ not only improves the excitation at ∼400 nm, but also changes the quantum efficiency and thermal stability of the phosphors. For example, the introduction of Y3+ increases the external quantum efficiency from 52 % to 62 %. The introduction of Ce3+, Y3+, and Lu3+ brings traps and therefore results in anti-thermal quenching behavior within 398 K. The pc-WLEDs fabricated by covering a 365/380 nm chip with phosphor blend containing K2CaPO4F:Eu2+,RE3+ can emit a warm white light with a CRI as high as 98. This work provides an effective approach to tune the luminescence properties for high performance solid-state lighting.