Annealing-induced evolution of structure, optical properties, and crystallisation kinetics in co-precipitated CdS nanoparticles

Cadmium sulphide (CdS) nanoparticles were synthesised via co-precipitation to investigate the effect of annealing temperature on their structural, optical, and morphological properties. The nanoparticles were annealed at 150–400 °C and studied by X-ray diffraction (XRD), UV-Vis spectroscopy, and scanning electron microscopy (SEM). The XRD results supported the creation of phase-pure hexagonal CdS, with no secondary phases detected. The crystallinity increased with increasing annealing temperature to 300 °C, yielding the largest crystallite size of 31.8 nm and the smallest full width at half maximum (FWHM) of 0.263°. With additional annealing, the crystallinity decreased considerably. Arrhenius’ analysis of the 150–300 °C temperature range yielded an activation energy of 14.1 kJ mol−1 (R2 = 0.9988), showing thermally activated crystallite formation. The UV-Vis study indicated higher optical transmittance with increasing annealing temperature, and SEM images showed well-defined nanoparticles with moderate aggregation at 300 °C. Overall, 300 °C was identified as most favourable annealing condition for achieving enhanced crystallinity and structural ordering.