Ca4(PO4)2O:Eu2+ red-emitting phosphor for solid-state lighting: structure, luminescent properties and white light emitting diode application

Abstract

A red-emitting phosphor, Eu²⁺-activated Ca₄(PO₄)₂O phosphor was synthesized by conventional solid-state reaction. X-ray powder diffraction confirmed the phase formation. The band gap of Ca₄(PO₄)₂O was estimated to be about 4.75 eV from the diffuse reflection spectrum. The excitation and emission spectra, and the concentration dependence of emission intensity were investigated. The results showed that under excitation at 460 nm, the Ca₄(PO₄)₂O:Eu²⁺ phosphors exhibit strong red emission centered at 665 nm, and the optimum concentration of Eu²⁺ in Ca₄(PO₄)₂O:Eu²⁺ is about 0.07 mol per mol Ca²⁺ ions. The nature of the Eu²⁺ ion emission in Ca₄(PO₄)₂O, i.e. the main mechanism for concentration quenching was discussed. A white LED was fabricated using a blue 460 nm chip pumped by a phosphor blend of green-emitting Sr₂SiO₄:Eu²⁺ and red-emitting Ca_3.93(PO₄)₂O:0.07Eu²⁺. When the applied current was 20 mA, the white LED has Commission International de I'Eclairage color coordinates of (0.3135, 0.3316) for white light (correlated color temperature = 6446 K) and an excellent color rendering index of 90.5.