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.

Graphical Abstract