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 (Mo6+) and acceptor-analogue (Sn4+) effects. XRD analysis confirms phase-pure hexagonal wurtzite structure (P63mc, JCPDS 36-1451) for all samples, except Zn0.95Mo0.04Sn0.01O (S2); crystallite size decreased from 72.38 nm (S1, undoped ZnO) to 27.51 nm (S5, Zn0.95Mo0.01Sn0.04O), 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 IUV/IVis 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.