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Photoluminescence of oxygen vacancies and hydroxyl group surface functionalized SnO_2 nanoparticles

We report, for the first time, the luminescence property of the hydroxyl group surface functionalized quantum dots (QDs) and nanoparticles (NPs) of SnO_2 using low energy excitations of 2.54 eV (488 nm) and 2.42 eV (514.5 nm). This luminescence is in addition to generally observed luminescence from 'O' defects. The as-prepared SnO_2 quantum dots (QDs) are annealed at different temperatures in ambient conditions to create varied NPs in size. Subsequently, average size of the NPs is calculated from the acoustic vibrations observed at low frequencies in the Raman spectra and by the transmission electron microscopic measurements. Detailed photoluminescence studies with 3.815 eV (325 nm) excitation reveal the nature of in-plane and bridging 'O' vacancies as well as adsorption and desorption occurred at different annealing temperatures. X-ray photoelectron spectroscopy studies also support this observation. Defect level related to the surface -OH functional groups shows a broad luminescence peak around 1.96 eV in SnO_2 NPs which is elaborated with the help of temperature dependent studies.