Double-Color Emitting SrSi₂O₂N₂:Eu²⁺,Yb²⁺Oxynitridosilicate Phosphor for Warm White-Light Emitting Diode with Highly Stable Color Chromaticity

Abstract

A green to orange emitting nitridosilicate based phosphor was developed for white-LED application. Observed broad-band emission in green to orange range is originated from Eu2+ and Yb2+-trap site of double doped SrSi2O2N2:Eu2+,Yb2+ nitridosilicate phosphor. Energy transfer between activator ions was confirmed by measuring of decay time of the green-emission as energy donor. The effect of co-doping by different ratio of activator ions on the photoluminescence properties was studied. Emission of the obtained phosphor is function of activator ion contents, and by increasing the Yb2+ concentration, the red emission dominants over green emission. The obtained phosphor was combined with InGaN blue-LED chip (λ = 450 nm) to create white-light. The color balance control was realized by two steps. At first green to orange ratio was optimized by adjusting concentration of Eu2+ and Yb2+ ions. At second step, by increasing amount of phosphor powder the CIE coordinates were shifted from [0.2805; 0.2014] to [0.4071; 03789]. At optimized condition generated white light has color rendering index about 89. The LED based on the developed single-phase double-color emitting nitridosilicate phosphor and blue-LED chip showed high color stability against wide range of forward-bias current (100 to 500 mA at 3 V).