Structural, morphological, optical, and photoluminescence characteristics of Mo/Sn co-doped ZnO nanoparticles synthesized via co-precipitation

Molybdenum (Mo) and tin (Sn) co-doped zinc oxide (ZnO) nanoparticles with systematically varied Mo:Sn ratios (total dopant fixed at 5 at%) were synthesized by co-precipitation to isolate competing donor (Mo 6+ ) and acceptor-analogue (Sn 4+ ) effects. XRD analysis confirms phase-pure hexagonal wurtzite structure (P63mc, JCPDS 36–1451) for all samples, except Zn 0.95 Mo 0.04 Sn 0.01 O (S2); crystallite size decreased from 72.38 nm (S1, undoped ZnO) to 27.51 nm (S5, Zn 0.95 Mo 0.01 Sn 0.04 O), and Williamson–Hall microstrain increased monotonically, confirming progressive lattice distortion. FESEM revealed a dopant-driven morphological evolution from hexagonal prismatic grains to flake-like and granular structures. UV–Vis absorbance spectra show an absorption edge at 373 nm for all samples; Tauc-plot bandgaps remain nearly constant (3.142–3.151 eV) owing to compensating Burstein–Moss widening and bandgap narrowing (BGN). Urbach energies rose from 95 meV (S2) to 178 meV (S5), corroborating increasing sub-bandgap disorder. PL spectra (325 nm excitation) show a 4.7-fold growth in NBE intensity from S1 to S5 and a monotonic decrease in I UV /I Vis from 3.8 to 0.7, demonstrating tuneable recombination pathway engineering. These results establish the Mo:Sn ratio as an effective compositional handle for directing ZnO nanoparticles towards UV-emitter or photocatalyst applications.