Structural and optical investigations of dual-site substituted cobalt ferrite nanoparticles

Abstract Dual-site substituted cobalt ferrite nanoparticles with the composition CoFe 2 O 4 :Ni 2 ⁺, Mn 2 ⁺(A-site)/Ce 3 ⁺(B-site) were synthesized via a glycolthermal method and examined for their structural and optical properties. X-ray diffraction confirmed a cubic spinel phase with minor CeO 2 secondary peaks at higher dopant levels. Doping slightly increased the lattice constant and microstrain while reducing crystallite size and X-ray density. Scanning Electron Microscopy and High-Resolution Transmission Electron Microscopy analyses revealed nanoparticle morphologies with agglomerations that became more pronounced upon doping. Energy Dispersive X-ray Spectroscopy confirmed the successful incorporation of Ni, Mn, and Ce ions into the lattice. Optical absorption spectra showed a tunable band gap from 2.84 (undoped) to 2.60 eV (30 mol% doped), while Urbach energy increased from 1.12 to 1.64 eV, indicating enhanced structural disorder and defect density. Photoluminescence spectra exhibited broad violet-to-green emissions dominated by defect-related and Ce 3 ⁺-induced transitions. CIE chromaticity analysis located all emissions in the orange region with high colour purity (80–84%) and correlated colour temperatures below 2000 K, corresponding to ultra-warm light. The study demonstrates that dual-site doping effectively tunes the structural and optical features of cobalt ferrite, making it a promising material for orange-red light-emitting and photocatalytic applications.