A novel single-phase warm white emission phosphor Sr3YAl2O7.5:Bi3+,Eu3+ with energy transfer for UV white LEDs

Abstract

A novel phosphor Sr₃YAl₂O_7.5:xBi³⁺,yEu³⁺ was successfully synthesized through a high temperature solid-state reaction. The crystal structure, photoluminescence properties, fluorescence decay and thermal quenching properties have been measured and analyzed. The energy transfer mechanism is demonstrated to be a dipole–dipole interaction and the critical distance between the Bi³⁺ and Eu³⁺ has been calculated. The emission spectra of the Sr₃YAl₂O_7.5:Bi³⁺,Eu³⁺ phosphors present a blue-green emission of Bi³⁺ ions with three broad bands at 370 nm, 410 nm and 505 nm and many characteristic emission lines of Eu³⁺ ions, deriving from the allowed ³P₁–¹S₀ transition of the Bi³⁺ ion and the ⁵D₀–⁷F_j transition of the Eu³⁺ ion. By changing the ratio of Bi³⁺ concentration and Eu³⁺ concentration, we can get a warm white light under ultraviolet excitation. The results give the Commission International deL'Eclairage (CIE) chromaticity coordinates for the white LED as (0.3794, 0.3453) and a correlated color temperature of 3731 K, and the integrated emission intensity at 150 °C remains 66.4% of that measured at room temperature, which indicates that the SYAO:Bi³⁺,Eu³⁺ phosphor is a very promising candidate for use as a warm UV white light-emitting diode (WLED) phosphor.