Site selective and enhanced blue emitting of Eu²⁺ activated fluorapatite-type phosphors with high color purity for NUV excited pc-wLEDs

Abstract

As blue emitting component in phosphor-converted white-light-emitting-diodes (pc-wLEDs) encapsulated with near-ultraviolet (NUV) chips, Eu2+ activated fluorapatite structure phosphors play key roles because of strong structural stability and excellent photoluminescent properties. A series of M5(PO4)3F: Eu2+ (M = Ca, Sr) samples have been newly prepared by deposition-precipitation process (DP) and exhibited a 6.7-fold enhancement of photoluminescent (PL) intensity due to the highly dispersed Eu2+ luminescence centers when compared with the reference samples synthesized via traditional solid-state reaction method (SSR). Detailed analysis of crystal field around Eu2+ and the nonlinear fitting of PL spectra concludes that Eu2+ activators with the 4f6 → 4f75d transition preferentially replace Ca1 in 4f symmetry sites leading to a fitted peak at 446 nm and the other sites of 6h are contributed to the 479 nm emitting of Eu2+ ions. Remarkably, tunable chromaticity of DP-M5(PO4)3F: Eu2+ with high color purity (97.79%) retains steady photoelectric converting and full width at half maxima (FWHM) of 46 nm in the device of DP-FAp: 0.03Eu2+@365 nm LED under diverse driving currents, which perfectly satisfies the requirements of excitation light source for oral photocuring materials. Further, the 123.4% color gamut of National Television System Committee (NTSC) standard is efficiently obtained by matching Sr5(PO4)3F: Eu2+, CsPbBr3 and Lu3Al5O12: Mn4+ phosphors with a 365 nm chip (1 W) to achieve high-quality white light (CRI value reaches to 86, CCT is 7107 K and CIE chromaticity coordinate arrives at (0.292, 0.376), indicating a potential candidate for dentistry curing light and high-quality NUV excited pc-wLEDs.