An efficient blue-emitting Sr5(PO4)3Cl:Eu2+ phosphor for application in near-UV white light-emitting diodes

Abstract

A series of Eu²⁺ doped Sr₅(PO₄)₃Cl blue-emitting phosphors was prepared by conventional high-temperature solid-state reactions. The crystal structure, electronic structure, reflectance spectra, thermal stability and quantum efficiency of the Sr₅(PO₄)₃Cl:Eu²⁺ phosphor, as well as its application in near-UV white light-emitting diodes have been investigated. The optimization of the lattice parameters and the electronic structure of the Sr₅(PO₄)₃Cl host matrix have been calculated based on density functional theory (DFT). The crystal structure of Sr₅(PO₄)₃Cl:Eu²⁺ was confirmed by X-ray diffraction. The concentration quenching of Eu²⁺ ions in the Sr₅(PO₄)₃Cl host is determined to be 1.0 mol% and the physical mechanism of concentration quenching can be explained by the dipole–dipole interaction. Through theoretical calculation, the color purity of the as-prepared Sr₅(PO₄)₃Cl:Eu²⁺ phosphor is found to be much better than the commercial compound, blue-emitting BaMgAl₁₀O₇:Eu²⁺ (BAM:Eu²⁺). In particular, a near-UV white LED was fabricated by using an InGaN-based near-UV LED chip (395 nm) and a mixture of Sr₅(PO₄)₃Cl:Eu²⁺, green-emitting (Ba,Sr)₂SiO₄:Eu²⁺ and red-emitting CaAlSiN₃:Eu²⁺ phosphors. The obtained LED device exhibits an excellent color-rendering index (R_a = 94.65) at a correlated color temperature of 3567.84 K with CIE coordinates (0.3952, 0.3709). The above results suggest that the Sr₅(PO₄)₃Cl:Eu²⁺ phosphor is a promising blue-emitting phosphor for application in near-UV white light-emitting diodes.