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 Sm 3+ -doped K 5 La(MoO 4 ) 4 phosphors were synthesized using the solid-state reaction method. The X-ray powder diffraction patterns and Rietveld refinement confirmed the single-phase structure of the synthesized K 5 La(MoO 4 ) 4 :Sm 3+ samples with trigonal system (space group R 3 ‾ $\bar{3}$ m (#166)). The phosphors demonstrated a strong red emission at 644 nm, corresponding to the electric dipole transition 4 G 5/2  →  6 H 9/2 of Sm 3+ ions. The optimal doping concentration for K 5 La (1- x ) ( MoO 4 ) 4 : x Sm 3+ 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. K 5 La (1- x ) ( MoO 4 ) 4 : x Sm 3+ phosphors displayed remarkable color stability with chromaticity coordinates falling within the red region in 1931 CIE diagram. K 5 La(MoO 4 ) 4 :5 mol%Sm 3+ 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, R a ) and correlated color temperature (CCT) of w-LED were 87 and 5627 K. These findings strongly suggest the potential use of K 5 La(MoO 4 ) 4 :Sm 3+ phosphors as red phosphors in LEDs.