Orange phosphor Li2SrSiON2:Eu2+ for blue light chip based warm white LEDs

Abstract

Oxynitride Li₂SrSiON₂ was synthesized by introducing N³⁻ into the Li₂SrSiO₄ lattice, which is suitable for Eu²⁺ doping. It crystallizes in an trigonal structure with the space group of P3₁21 (152) and cell parameter a = b = 5.0131(0) Å, c = 12.4270(1) Å and V = 270.46 ų. Under blue light (450 nm) excitation, the representative sample Li₂Sr_0.98SiON₂:0.02Eu²⁺ exhibits a bright broad band orange emission peaking at 586 nm with an external quantum efficiency of 52.7%. Its emission intensity at 150 °C remained 78% of that measured at 25 °C. Warm white light-emitting diode 1 (W-LED1) was prepared by combining a blue LED chip and LSSON:0.02Eu²⁺. High color rendering index (R_a ∼ 90) warm W-LED2 was fabricated by combing a blue light chip, BaSi₂O₂N₂:Eu²⁺, and Li₂Sr_0.98SiON₂:0.02Eu²⁺. The chromaticity coordinate and correlated color temperature (CCT) of W-LED2 are (0.3625, 0.3539) and ∼4386 K, respectively. Excellent optical properties allow it to be an attractive orange phosphor for warm W-LEDs.