Abstract
Cadmium sulfide nanoparticles with tunable optical properties were synthesized using two methods: Successive Ionic Layer Adsorption and Reaction and sonochemical synthesis, with Cd:S molar ratios varied from 1:0.1 to 1:1. The SILAR method produced flexible CdS/polyvinyl alcohol composite films, while the sonochemical method yielded highly crystalline CdS powders under ambient conditions. Structural analysis revealed phase transitions from hexagonal to mixed cubic–hexagonal and amorphous structures depending on sulfur concentration, demonstrating the critical role of precursor stoichiometry.

Optical characterization showed a decrease in the band gap with increasing sulfur content, attributed to quantum confinement effects and defect state modulation. Photoluminescence measurements under 330 nm excitation indicated that emission intensity, spectral position, and broadening were significantly influenced by synthesis route and stoichiometry. Sonochemically synthesized nanoparticles exhibited broad, defect-related emissions, while SILAR-based CdS/PVA films displayed more intense, red-shifted, and stable luminescence due to exciton confinement and polymer interaction.

The highest PL efficiency was observed at a 1:0.25 Cd:S ratio, providing an optimal balance between crystallinity and defect density. These findings demonstrate that synthesis method, stoichiometry, and matrix environment critically affect the structural and photoluminescent properties of CdS nanoparticles, offering practical insights for tailoring these materials for optoelectronic and photonic applications.
These results confirm that the synthesis method and stoichiometry critically influence the emission, defect structure, and crystal phase of CdS nanoparticles, enabling tunable properties for optoelectronic and photocatalytic use.