Experimental and theoretical insights into the structural, optical, and magnetic properties of Co doped CdSe: A combined XRD, UV-Vis, and DFT study

This study explores the structural, optical, and magnetic transformations in cobalt-doped cadmium selenide (CdSe:Co) thin films, synthesized via chemical bath deposition (0–11 mol%) and modeled using density functional theory (DFT). X-ray diffraction (XRD) confirms a cubic zinc-blende structure, where Co doping induces a transition to a highly crystalline state at 11 mol%, despite the emergence of a secondary CoSe 2 phase. Scanning electron microscopy (SEM) reveals a significant morphological shift from isolated macro-spheres to dense cauliflower-like polycrystalline clusters. UV-Vis spectroscopy demonstrates a systematic bandgap narrowing (2.06–1.98 eV) and a pronounced redshift in the absorption edge, while photoluminescence (PL) analysis exhibits concentration quenching with a unique intensity recovery at 11 mol%, attributed to dopant-induced localized state sequestration. Complementary DFT calculations using the SIESTA package provide a microscopic rationale for these observations, revealing a significant bond contraction (Co–Se: 2.42 Å) and strong sp − d exchange interactions. Spin-polarized density of states (DOS) and band structure analyses confirm the material's evolution into a diluted magnetic semiconductor (DMS) with a calculated spin magnetic moment of 3.00 μB per Co atom. Furthermore, theoretical optical conductivity shows enhanced infrared activity driven by intra-band d - d transitions. The convergence of experimental and theoretical results identifies Co doped CdSe as a versatile candidate for both high-efficiency solar energy conversion and advanced spintronic technologies.