Understanding the structure-property correlation of tin oxide nanoparticles synthesized through the sol-gel technique

The present study aims at exploring the structural, morphological, optical, defects and phase related aspects of the sol-gel synthesized highly pure tin oxide (SnO2) nanocrystallites as a function of sample annealing temperature by carrying out experiments using various spectroscopic and analytical techniques. The X-ray diffraction (XRD) and high resolution transmission electron microscopic (HRTEM) studies confirmed the nanocrystallinity of the samples as the average sizes of the crystallites were found in between 10 and 20 nm. Williamson – Hall (W − H) analysis was employed for estimating the lattice strain and exact crystallite size of nanoparticles (NPs). The monotonous decrease of lattice strain with sample annealing temperature is consistent with increase of crystallite size by increase in temperature. The NPs exhibited some specific anomalous behaviour, among which a prominent one is the increased lattice parameters and unit cell volumes with the decrease of crystallite sizes. The optical band gap was observed to increase when the nanocrystallites became smaller in size. The latter aspect is attributable to the onset of quantum confinement effect, as observed in a few other metal oxide NPs. The atomic vibrations were characterized through distinct absorbance bands appeared in Fourier-transform infrared (FT-IR) spectroscopy. The photo-induced luminescence properties were studied by Fluorescence (FL) spectroscopy in terms of defects and/or oxygen vacancies related transitions. Positron annihilation lifetime spectroscopy (PALS) was employed to study the vacancy type defects, which were abundant in the samples and played crucial roles in modulating their properties. The results suggest the feasibility of tailoring the properties of SnO2 NPs synthesized through sol-gel route-for technological applications. It also provides the physical insight into the structural build-up process when crystallites were formed with a finite number of atoms, and their distributions were governed by the site stabilization energy. Since the samples of smaller crystallite sizes have remarkably larger defect concentrations.