Blue-emitting Ca5(PO4)3Cl:Eu2+ phosphor for near-UV pumped light emitting diodes: Electronic structures, luminescence properties and LED fabrications

Abstract

A blue-emitting Ca5(PO4)3Cl:Eu2+ phosphor was prepared via a conventional high temperature solid-state reaction method. Crystal and electronic structure properties of the Ca5(PO4)3Cl:Eu2+ phosphor were investigated using X-ray diffraction and density functional theory (DFT), respectively. The micro-morphology, reflectance spectra, thermal stability and quantum efficiency of the Ca5(PO4)3Cl:Eu2+ phosphor were also studied. The optimum Eu2+ concentration in Ca5(PO4)3Cl was determined to be 2.0 mol% and the concentration quenching mechanism can be explained by the dipole–dipole interaction. The emission intensity of the Ca5(PO4)3Cl:Eu2+ phosphor was 58.2% of the initial value when the measured temperature increased from 30 °C to 150 °C. The activation energy was determined to be 0.254 eV, suggesting the good stability of this phosphor. A bright blue LED was fabricated using an InGaN-based near-UV LED chip (385 nm) and a Ca5(PO4)3Cl:Eu2+ phosphor, and has an excellent blue-emitting property with CIE coordinates of (0.1480, 0.0350). Furthermore, a bright near-UV warm white LED was fabricated using an InGaN-based near-UV LED chip (395 nm) in combination with the present blue phosphor and the commercial green and red phosphors, which exhibits an excellent color-rendering index (Ra = 96.65) at a warm correlated color temperature of 3902 K with CIE coordinates of (0.3781, 0.3879). All the results suggest that the Ca5(PO4)3Cl:Eu2+ phosphor is a potential blue-emitting candidate for the application in the near-UV pumped blue and warm white LEDs.