Nanoparticle size, oxidation state, and sensing response of tin oxide nanopowders using Raman spectroscopy

Highlights: • Tin oxide nanopowders were synthesized by sol–gel method. • The structural and surface properties are studied using XRD, TEM, and Raman. • A_1g Raman mode used to determine the nanocrystal sizes by phonon confinement model. • The changes in the low frequency Raman spectra is used to study the oxidation state. • Optical sensing response of tin oxide to ammonia gas and 2-nitrophenol are testified using Raman. - Abstract: Tin oxide nanopowders were prepared by a sol–gel method and annealed at different temperatures in an oxygen atmosphere. The amorphous-to-crystalline transformation, the evolution of the nanocrystals, the sizes and their distribution, the surface characteristics, and the degree of oxidation as a function of annealing temperature are all determined from the Raman spectra. The changes in the Raman spectra between 100 and 200 cm⁻¹ represent the change in the oxidation state. The A_1g mode, which is a signature of a crystalline SnO₂ phase, is used to determine the nanocrystal sizes. The Raman spectra clearly reveal the gradual transformation of Sn(OH)₂ to SnO_x and ultimately to SnO₂ with annealing. The crystallinity and crystallite sizes are also confirmed with X-ray diffraction and transmission electron microscopy measurements. Furthermore, Raman spectroscopy is utilized to study the sensing response of the thus synthesized SnO_x to NH₃ gas and 2-nitrophenol. Raman spectroscopy is thus demonstrated to be a rapid and comprehensive technique to determine a multitude of parameters of tin oxide relevant for sensing applications