eng Science and Education Publishing International Journal of Physics 2333-4576 2025-06-17 13 3 49 54 10.12691/ijp-13-3-1 IJP20251331 article Ogechi Ogana John johnogechi2012@yahoo.com 1 Daniel Ketui 1 Duke Oeba 2 Department of physics, Kisii University, Nairobi, Kenya Department of physics, Egerton University, Nairobi, Kenya Cadmium sulphide (CdS) thin films were prepared on glass substrates using the spin-coating technique from a precursor solution containing cadmium nitrate tetrahydrate (Cd(NO?)??4H?O), indium nitrate hydrate (In(NO?)??xH?O), thiourea (CH?N?S), and ammonium nitrate (NH?NO?). This study focused on synthesizing indium-doped CdS thin films via spin coating and examining how varying indium concentrations (0.004 M, 0.006 M, 0.008 M, and 0.010 M) affect the structural and optical properties of the films. The resulting thin films were analyzed using several characterization techniques, including X-ray diffraction (XRD), UV-Visible spectroscopy (UV-Vis), and scanning electron microscopy (SEM). Analysis of the absorbance spectra indicated that the optical band gap energy ranged from 3.63 eV to 3.88 eV, with the highest value observed at an indium concentration of 0.008 M. Optical measurements obtained through UV-Vis spectrophotometry confirmed high transparency within the visible region. These findings suggest that increasing the indium content leads to a widening of the band gap. https://pubs.sciepub.com/ijp/13/3/1/ijp-13-3-1.pdf Spin Coating Thin films Optical Properties morphological properties and structural properties