Nanophosphor materials are capturing the interest of researchers for their potential applications in light sources, information display panels, radiation converters, fluorescent pigments, and tracers. These materials consist of nanoparticles wherein a transparent host compound is doped with optically active materials, emitting light due to electronic transitions between impurity centers and the band gap of the host lattice. The band-to-band transition strongly relies on the band gap, affecting the luminescence behavior as a result of quantum confinement. Therefore, controlling the particle size is crucial to optimize the performance of phosphor materials in fluorescent devices, light-emitting diodes (LEDs), and display panels. Several nanophosphors have been synthesized mostly as powders with a few exceptions in matrices and as films using different techniques [1-2]. In this study, we investigated the structural, morphological, optical, and photoluminescence properties of Zn3-xMx(PO4)2 (M=Co, Ni) nanoparticles with (x=1), synthesized using the solid-state method. The optical constants and dispersion energy parameters of the nanoparticles were determined using UV-visible optical characterization. The optical band gap was measured to be 2.48 eV for Zn3(PO4)2, 3.05 eV for Zn2Ni(PO4)2 nanoparticles, and 3.12 eV for Zn2Co(PO4)2. The refractive index dispersion of Zn3(PO4)2 followed the single-oscillator model. The real and imaginary parts of the dielectric constant of Zn3-xMx(PO4)2 (M=Co, Ni) nanoparticles with (x=1) were also determined. The photoluminescence spectra of Zn3(PO4)2 exhibited a peak around 2.56 eV, while the Zn2Co(PO4)2 nanoparticles showed peaks at 3.26 Ev and Zn2Ni(PO4)2 had a peak at 2.47 eV . These absorption spectra peaks are attributed to the recombination of excitons and/or shallowly trapped electron–hole pairs, representing band-edge emission.