TiO2 sol–gel thin films: effect of acidic and basic pH on physical characteristics.

The present study examines the impact of acidic and basic pH on the optical, morphological, and structural characteristics of TiO₂ sol–gel thin films that are deposited using the dip-coating technique on glass substrates. All of the samples are polycrystalline and have anatase structures with preference orientation along the (101) direction, according to X-ray diffraction (XRD) and Raman spectroscopy (RS). It is observed that, for both basic and acidic pH values, crystallite size decreases as sol pH rises. All of the films' surfaces were smooth and had a uniform grain distribution, according to atomic force microscopy (AFM). The pH of the sol has an impact on the surface roughness. All films had a higher degree of transparency, according to UV-visible spectroscopy. The refractive index and the direct and indirect band gaps are two essential optical properties of thin films that are significantly influenced by the pH of the deposition medium. Measurements of photoluminescence (PL) showed a strong violet-blue emission band, the intensity of which is highly dependent on the sol's pH. In acidic media, PL decreases with increasing pH. However, in a basic environment, the PL rises sharply as the pH increases from 10 to 11 and then decreases for higher pH values. In particular, compared to the other samples, the emission intensity from the film deposited at a pH value of 10 is noticeably lower and displays unique spectral signatures. Highlights: The effects of acidic and basic pH on the structural, morphological, and optical properties of TiO₂ sol–gel thin films were investigated. XRD analyses show that crystallite size decreases with increasing pH in both acidic and basic sols. Optical analysis demonstrates that TiO₂ thin films deposited at acidic pH values have greater transparency than those deposited at basic pH values. Photoluminescence measurements revealed a strong correlation between sample emission and pH. The film deposited at pH 10 has significantly lower emission intensity and a distinct spectral signature than the other samples. [ABSTRACT FROM AUTHOR]