Tin oxide nanocrystals: controllable synthesis, characterization, optical properties and mechanistic insights into the formation process

Abstract

A novel, surfactant-free, solution-phase method has been successfully developed for the synthesis of SnO2 nanocrystals using a solvothermal route. The nanocrystals having average diameters in the range 4–8 nm, have been synthesized by a non-aqueous sol–gel reaction using tin(IV) bis(acetylacetonate)dichloride, [(Sn(acac)2Cl2)] with benzyl alcohol as the reaction medium at 200 °C. The crystal structure, morphology, and sizes of the SnO2 nanocrystals have been determined by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman studies. Raman peaks at 627, 768 cm−1 characteristic of the rutile phase of bulk SnO2 are observed along with broad surface vibration modes in the range 400–600 cm−1. Optical properties of the nanocrystals have been explored by optical absorption and photoluminescence (PL). A blue shift of the optical band gap of the nanocrystals is observed due to size effects. The estimated band gap of the SnO2 nanocrystals from optical absorption data is found to be 3.81 eV. The photoluminescence spectrum showed broad UV as well as visible emission. Based on the GC-MS and carbon-13 NMR analysis of the final reaction solution, a formation mechanism encompassing the ether elimination and solvolysis of acetylacetonate ligand is proposed.