Comparative study of different europium doping techniques on the structural and optical properties of ZnO nanoparticles

Zinc oxide nanoparticles (ZnO NPs) were synthesized via a co-precipitation method and doped with Eu 3+ ions using three different approaches: in-situ doping during synthesis (Eu:ZnO(P)), post-synthesis doping (Eu:ZnO(S)), and modification of commercially available ZnO (Eu:ZnO(C)). Structural analysis by X-ray diffraction (XRD) confirmed the preservation of the hexagonal wurtzite phase in all samples, while peak shifts and broadening indicated lattice distortion associated with Eu 3+ incorporation. The crystallite size decreased from 24 to 16 nm for Eu:ZnO(S) and from 61 to 36 nm for Eu:ZnO(C), demonstrating the influence of the doping route on crystal growth. Optical characterization using UV–Vis spectroscopy demonstrated band-gap narrowing from 3.05 to 2.95 eV for Eu:ZnO(C), from 3.00 to 2.90 eV for Eu:ZnO(S), and to 2.85 eV for Eu:ZnO(P). Photoluminescence (PL) analysis revealed enhanced emission intensity and a redshift in doped samples, attributed to defect-related states associated with Eu incorporation. Among all samples, Eu:ZnO(S) exhibited the highest PL intensity and a pronounced emission band near 592 nm, highlighting the effectiveness of post-synthesis doping. These findings demonstrate that the doping strategy and nanoparticle origin play a crucial role in tailoring the structural and optical properties of ZnO nanomaterials for potential optoelectronic and photonic applications.