Precursor Concentration–Driven Modulation of harmonic generation responses in TiO2 nanostructures for sustainable photonic devices

In this study, precursor molarity is demonstrated as an effective tuning parameter for tailoring the structural, optical, and nonlinear optical properties of spray pyrolyzed TiO 2 thin films, deposited with precursor concentration varying from 0.05 M to 0.2 M. XRD confirmed the formation of polycrystalline anatase TiO 2 with a preferred orientation along the (101) plane. The size of the crystallites increased from 40.3 nm at 0.05 M to the highest value of 46.8 nm at 0.10 M, then decreased to 27.0 nm at 0.20 M. Raman spectroscopy further verified the phase purity of anatase TiO 2 , evidenced by the characteristic Raman peak at 144 cm −1 . Optical studies revealed a tunable indirect band gap in the range of 3.25 eV to 3.42 eV. AFM revealed improved surface smoothness with increasing precursor concentration, as evidenced by a decrease in average roughness from 1.84 nm to 0.37 nm. PL intensity increased at 0.1 M due to enhanced radiative recombination and decreased at 0.2 M owing to the dominance of non-radiative centers. Z-scan measurements showed maximum nonlinear absorption of 5.39 × 10 −1 m/W at precursor concentration of 0.05 M. Higher concentrations promoted enhanced second- and third-harmonic generation attributed to defect-mediated carrier dynamics. These findings highlight precursor concentration as a sustainable design parameter for optimizing TiO 2 thin films in optical limiting and ultrafast photonic devices.