Spectroscopic investigation of K5La(MoO4)4:Sm3+red phosphor with excellent thermal stability and color purity for white LEDs

In this study, a series of innovative red-emitting Sm3+-doped K5La(MoO4)4 phosphors were synthesized using the solid-state reaction method. The X-ray powder diffraction patterns and Rietveld refinement confirmed the singlephase structure of the synthesized K5La(MoO4)4:Sm3+ samples with trigonal system (space group R 3 m (#166)). The phosphors demonstrated a strong red emission at 644 nm, corresponding to the electric dipole transition 4G5/ 2 -> 6H9/2 of Sm3+ ions. The optimal doping concentration for K5La(1-x) (MoO4)4:xSm3+ was found to be approximately 5 mol%. The temperature-dependent emission of phosphors was examined and found that the luminescence intensity remained at 86 % even at 480 K, showing the exceptional thermal stability of this material. K5La(1-x) (MoO4)4:xSm3+ phosphors displayed remarkable color stability with chromaticity coordinates falling within the red region in 1931 CIE diagram. K5La(MoO4)4:5 mol%Sm3+ exhibited a high color purity of 99.9 % and internal quantum efficiency (IQE) was measured as 66.8 %. Light-emitting diodes (LEDs) were constructed using InGaN chips and the synthesized red phosphors. The chromaticity coordinates of the fabricated w-LED (white light-emitting diode) were (0.330, 0.351), closely resembling the typical white point of the National Television System Committee (NTSC) at (0.333, 0.333). The color rendering index (CRI, Ra) and correlated color temperature (CCT) of w-LED were 87 and 5627 K. These findings strongly suggest the potential use of K5La (MoO4)4:Sm3+ phosphors as red phosphors in LEDs.