Design of novel cyan phosphor Ca7NaLu(PO4)6:Eu2+ for full-visible-spectrum white LED: enhanced thermal stability and tuned emission by neighbor cation effect

Abstract

Cyan phosphor is desirable to fill the cyan gap (480–520 nm) in white light-emitting diodes (wLEDs) to achieve full-visible-spectrum lighting. In this paper, a novel highly efficient cyan emitting Ca7NaLu(PO4)6:Eu2+ (CNLP:Eu2+) phosphor was synthesized, exhibiting broadband and bright emission ranging from 425 to 675 nm and an excitation band ranging from 250 to 450 nm. Notably, CNLP:0.09Eu2+ shows an excellent internal quantum efficiency of 90% and a high external quantum efficiency of 57.6%. In addition, a neighbor cation effect induced by replacing Ca with Sr was used to design a series of Ca7-ySryNaLu(PO4)6:Eu2+ (C7-ySyNLP:Eu2+y = 1, 4, 7) phosphors with a good thermal stability and tunable emission. The spectra of the C7-ySyNLP:Eu2+ phosphors undergo a red shift and the full width at half maximum increase from 78 to 100 nm with an increase of Sr content. Furthermore, a near-ultraviolet pumped wLED that fills the cyan gap was fabricated by composing CNLP:0.09Eu2+ with commercial phosphors, showing high color rendering index (Ra = 95). The excellent luminescent properties of as-prepared phosphors indicate they are promising for the production of high-color rendering index full-visible-spectrum wLEDs.