Microstructure-Dependent Optical Transparency and Band Gap Engineering in SnO₂ Nanomaterials

Abstract

The schematic illustrates the synthesis–structure–property correlation in SnO₂
nanostructures. The diagram depicts (i) the formation of tetragonal rutile SnO₂, confirmed by
XRD analysis with a dominant (110) orientation; (ii) nanostructured morphology influencing
crystallite size and lattice strain; and (iii) optical transparency with high visible transmittance
(65–75%) and a sharp UV absorption edge corresponding to direct and indirect optical
bandgap energies (~3.5–3.6 eV), which were estimated and found to decrease with film
thickness. The diagram highlights the relationship among crystallinity, defect states (Urbach
tail), which are related to disorder and localized states, and the estimated decrease in film
thickness and optical band gap modulation, demonstrating the suitability of the synthesized
SnO₂ for optoelectronic and gas-sensing applications.