SM³⁺-Activated LiZnPO₄ Phosphors: Synthesis, Characterization, and Their Luminescent Properties for White Light-Emitting Diode Applications

This work presents a comprehensive analysis of the synthesis, structural–spectroscopic characterization, thermal stability, and luminescent attributes of Sm³⁺-activated LiZnPO₄ phosphors with diverse Sm³⁺ doping percentiles that work towards developing luminescent materials for white-light-emitting diode (WLED) applications. The polycrystalline samples of LiZn_{(1 − x)} Sm_x³⁺PO₄ (x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, and 0.10) phosphor were synthesized using a solid-state reaction (SSR) technique. X-ray diffraction (XRD) and Rietveld refinement indicate a single-phase monoclinic structure of all compositions with the C1c1 space group. Phase purity and stoichiometry of elemental composition were validated by Fourier transform infrared (FTIR) spectroscopy and energy-dispersive spectroscopy (EDS) examination. Field-emission scanning electron microscopy (FE-SEM) images indicate irregular and nonuniform microstructures for all compositions with a mean dimension of 1.252 µm. The investigation of diffuse reflectance (DR) spectra with the Kubelka–Munk function F(R_∞) determines the compound's bandgap to be 3.1 eV. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) indicates various ions are regularly distributed across the surface. Further, the photometric analysis reveals that the Commission Internationale de l'Éclairage (CIE) coordinates are roughly (0.55, 0.44), and color purity is greater than 82% in all compositions. These results, along with the photoluminescence (PL) spectral analysis, lifetime analysis, and thermal stability, indicate that Sm³⁺-doped LiZnPO₄ is a viable orange-red-emitting phosphor candidate for creating white-light-emitting diodes (WLEDs).