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Description
NaYF4 nanoparticles were synthesized using a solution combustion method at 500 °C and subsequently annealed at 700 °C to investigate the effect of thermal treatment on their structural, optical, and thermoluminescent properties for dosimetric application. X-ray diffraction (XRD) analysis confirmed the coexistence of cubic and hexagonal phases in both samples, while annealing led to enhanced crystallinity, as evidenced by peak sharpening, increased crystallite size, reduced lattice strain and dislocation density. Raman spectroscopy further revealed improved lattice ordering through the emergence of sharper vibrational modes, consistent with structural refinement. Scanning electron microscopy (SEM) showed a transition from highly agglomerated, fine particles in the as-prepared sample to larger, coalesced grains with smoother morphology after annealing. Optical absorption studies indicated significant modification of the electronic structure, with the band gap decreasing from ~5.07 eV to 3.45 eV following annealing. Thermoluminescence (TL) analysis revealed a dominant low-temperature glow peak in both samples. After annealing, the glow peak shifted slightly towards higher temperature with reduced intensity, indicating a decrease in shallow trapping centres and the formation of more thermally stable traps. The TL intensity increased linearly with radiation dose, confirming first-order kinetics and demonstrating suitability for dosimetric applications. Repeatability measurements showed stable TL response with coefficient of variation values below 5% for both samples. Activation energies determined using the initial rise (IR) method were 0.59 ± 0.01 eV and 0.62 ± 0.01 eV for the as-prepared and annealed samples, respectively, indicating improved trap stability after annealing. These results demonstrate that thermal annealing significantly modifies the defect structure and trapping characteristics of NaYF4, making it a promising candidate for stable thermoluminescent dosimetry applications.
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