Orange- to green-emitting Li(Sr,Ca)4(BO3)3:Eu2+ phosphor: emission-tunable properties and white light emitting diode application

Abstract

An emission-tunable phosphor, Eu²⁺-activated LiSr_(4−x−y)Ca_x(BO₃)₃:yEu²⁺ phosphor, was synthesized by high temperature solid state reaction. By combining with Reitveld refinement analysis, the X-ray powder diffraction test confirmed the formation of a crystalline phase. The optical spectral properties, concentration quenching properties, decay curves and thermal stability of the LiSr_(4−x−y)Ca_x(BO₃)₃:yEu²⁺ phosphor were investigated in detail. The results showed that with the Ca²⁺ doping concentration increasing, the emission maxima is shifted from 618 to 501 nm and the color hue can be tuned from orange red to blue green. The effects of Ca²⁺ substitutions into Sr²⁺ sites on the emission band change were investigated. A white LED was fabricated using a blue 450 nm chip pumped by LiSr_3.92Ca_0.06(BO₃)₃:0.02Eu²⁺ phosphor film. Under 100 mA driven currents, the white LED device has a Commission International de I'Eclairage (CIE) color coordinate of (0.3563, 0.3576) at a white light (correlated color temperature = 5083 K) and an excellent color rendering indices of 85.3.