Abstract <p>This study examined Pb-doped ZnO thin films deposited on glass by spray pyrolysis, with Pb concentrations from 0 to 4 at.%. X-ray diffraction confirmed a hexagonal wurtzite structure with strong (002) orientation. Pb incorporation expanded the lattice and increased crystallite size from 16.7 (undoped) to 35.4 nm (4 at.%). UV–Vis spectroscopy revealed bandgap widening from 3.22 to 3.42 eV, mainly due to the Burstein–Moss shift. Photoluminescence showed unchanged point-defect emission. Atomic force microscopy revealed a transition from dome-like grains to elongated features, accompanied by a reduction in roughness from 9.08 to 4.01 nm. Prism coupler waveguiding confirmed dual-mode in all films. Pb doping raised ordinary and extraordinary refractive indices from 1.9678 and 1.9754 to 2.0046 and 2.0188, exceeding bulk ZnO values. Birefringence remained positive, while the extinction coefficient decreased by 32%, from 0.02137 to 0.01438. The confinement coefficient of the <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathrm TE_1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="normal">T</mi> <msub> <mi>E</mi> <mn>1</mn> </msub> </mrow> </math></EquationSource> </InlineEquation> mode increased by 2%.</p> Graphic abstract <p></p>