Role of anionic substitution (F ⁻ , MoO ₄ ²⁻ and WO ₄ ²⁻ ) on the structural, optical, and photoluminescence properties of Bi ^3- activated ZnO nanostructures

Abstract

Abstract ZnO nanostructures co-doped with 1 mol% Bi 3+ and different anionic species (F − , MoO 4 2− and WO 4 2− ) were synthesized via a solution combustion method and systematically investigated for their structural, optical, and photoluminescence properties. X-ray diffraction and Rietveld refinement confirmed the formation of a single-phase hexagonal wurtzite structure with slight lattice distortion upon dopant incorporation. Diffuse reflectance analysis revealed subtle band gap modulation associated with defect-induced localized states. Photoluminescence studies demonstrated that F − incorporation enhances near-band-edge emission by suppressing non-radiative recombination centres, whereas MoO 4 2− and WO 4 2− co-doping results in enhanced visible emission, possibly due to charge-transfer interactions and modifications of the local electronic environment. Among the samples investigated, ZnO:Bi 3+ /WO 4 2− exhibited the highest emission intensity, highlighting the significant role of WO 4 2− in tuning the luminescence properties of the ZnO host. The combined influence of Bi 3+ activation and anion engineering enables tunable broadband visible emission spanning the cyan-to-green spectral region. The enhanced luminescence observed in the co-doped samples may be associated with changes in defect chemistry and possible charge-transfer interactions involving the incorporated anionic species; however, direct confirmation of these processes requires further time-resolved spectroscopic studies. These findings highlight anion substitution as an effective strategy for tailoring the luminescence properties of ZnO-based phosphors for colour-tunable lighting and optoelectronic applications.