Nanosized Eu-Doped NaYSiO Oxyapatite Phosphor: A Comprehensive Insight into Its Hydrothermal Synthesis and Structural, Morphological, Electronic, and Optical Properties.

Detailed analysis covered the optical and structural properties of Eu-doped NaYSiO oxyapatite phosphors, which were obtained via hydrothermal synthesis. X-ray diffraction patterns of NaYSiO:xEu (x = 0, 1, 5, 7, 10 mol% Eu) samples proved a single-phase hexagonal structure ( (176) space group). Differential thermal analysis showed an exothermic peak at 995 °C attributed to the amorphous to crystalline transformation of NaYSiO. Electron microscopy showed agglomerates composed of round-shaped nanoparticles ~53 nm in size. Room temperature photoluminescent emission spectra consisted of emission bands in the visible spectral region corresponding to D → F ( = 0, 1, 2, 3, 4) transitions of Eu. Lifetime measurements showed that the Eu concentration had no substantial effect on the rather long D-level lifetime. The Eu energy levels in the structure were determined using room-temperature excitation/emission spectra. Using the F manifold, the Nv-crystal field strength parameter was calculated to be 1442.65 cm. Structural, electronic, and optical properties were calculated to determine the band gap value, density of states, and index of refraction. The calculated direct band gap value was 4.665 eV (local density approximation) and 3.765 eV (general gradient approximation). Finally, the complete Judd-Ofelt analysis performed on all samples confirmed the experimental findings.