Structural and optical characterization of Ni–Zn and Sn–Zn co-doped CdS nanoparticles synthesized via hydrothermal method

The pure CdS, Zn-doped CdS, and Zn–Ni as well as Zn–Sn co-doped CdS nanoparticles were successfully synthesized via the hydrothermal method, and their structural and optical properties were systematically investigated. A fixed Zn concentration of 10 mol% was employed, while Ni and Sn were introduced at concentrations of 2 and 4 mol% to examine their effects on the crystal structure and optical behavior of CdS nanoparticles. X-ray diffraction (XRD) analysis confirmed the successful formation of crystalline CdS nanoparticles with mixed cubic (Hawleyite) and hexagonal (Greenockite) phases depending on the dopant composition. The average crystallite size determined by the Scherrer method ranged from 23.99 to 40.06 nm, while the Williamson–Hall and Monshi–Scherrer methods yielded crystallite sizes of 20.40–44.56 nm and 22.12–42.32 nm, respectively. The corresponding lattice microstrain values varied from 2.76 × 10⁻³ to 7.26 × 10⁻³ , confirming that dopant incorporation significantly influenced crystal growth and lattice distortion. FTIR spectroscopy verified the successful incorporation of Zn, Ni, and Sn ions into the CdS lattice through characteristic Cd–S vibrational bands without the formation of secondary impurity phases. UV–Visible spectroscopy revealed strong ultraviolet absorption and an average visible-light transmittance of approximately 81%, indicating excellent optical transparency. The optical band gap, estimated using the Tauc method, varied from 5.09 to 5.63 eV, demonstrating that co-doping effectively modified the optical properties of CdS nanoparticles.