Tunable Eu2+ emission in K_xNa_1-xLuS₂ phosphors for white LED application

Highlights: • Novel Eu²⁺-doped K_xNa_1-xLuS₂ (x = 0-1) crystals were synthesized by chemical reaction under the flow of hydrogen sulfide. • Structural, optical and paramagnetic characteristics of Eu²⁺-doped K_xNa_1-xLuS₂ (x = 0-1) are reported for the first time. • Possibility to construct circadian white LED, demonstrated by a simultaneous use of near UV and blue LEDs. • CIE color coordinates and two examples of white color with different temperatures are modeled. • The realistic application potential of studied materials in white LEDs is discussed in detail. Set of Eu²⁺-doped K_xNa_{1 − x}LuS₂ phosphors (x = 0–1) in the form of transparent crystalline hexagonal platelets was successfully synthesized by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, X-ray fluorescence, time-resolved luminescence spectroscopy and electron paramagnetic resonance. Special attention was given to photoluminescence emission spectra under the 395 nm and 455 nm excitation aiming to obtain white emission with tunable color temperature. EPR method was employed to understand the Eu²⁺ incorporation and distribution in the K_xNa_{1 − x}LuS₂ hosts. CIE xy-coordinates were calculated to compare effects of different K/Na concentration in K_xNa_{1 − x}LuS₂ on resulting spectrum. The application potential of mentioned compounds in the field of white LED solid state lighting phosphors is thoroughly discussed.