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Local symmetry breaking in SnO2 nanocrystals with cobalt doping and its effect on the optical properties.


X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to study structural and morphological characteristics of cobalt doped tin (IV) oxide (Sn1xCoxO2; 0 x 0.04) nanocrystals synthesized by chemical coprecipitation technique. Electronic structure analysis using X-ray photoemission spectroscopy (XPS) show the formation of tin interstitials (Sni) and reduction of oxygen vacancies (VO) in the host lattice on Co doping and that the doped Co exists in mixed valence states of +2 and +3. Using XRD, the preferential position of the Sni and doped Co in the unit cell of the nanocrystals have been estimated. Rietveld refinement of XRD data show that samples are of single phase and variation of lattice constants follows the Vegard’s law. XRD and TEM measurements show that the crystallite size of the nanocrystals decrease with increase in Co doping concentration. SAED patterns confirm the monocrystalline nature of the samples. Study of the lattice dynamics using Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy show the existence of many disorder activated forbidden optical phonon modes, along with the corresponding classical modes, signifying the Co induced local symmetry breaking in the nanocrystals. UV-Vis spectroscopy shows that the optical band gap has red shifted with increase in doping concentration. Study on Urbach energy confirms the increase in disorder in the nanocrystals with Co doping. Local symmetry breaking induced UV emission along with violet, blue and green luminescence has been observed from the PL study. The spectral contribution of UV emission decreases and green luminescence increases with increase in doping. Using PL, in conjunction with the Raman spectroscopy, the type of oxygen vacancy induced in the nanocrystals on Co doping has been confirmed and the position of the defect levels in the forbidden zone (w.r.t. the optical band gap) have been studied.

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Publication details

The article was received on 06 Oct 2017, accepted on 14 May 2018 and first published on 15 May 2018

Article type: Paper
DOI: 10.1039/C7NR07427A
Citation: Nanoscale, 2018, Accepted Manuscript
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    Local symmetry breaking in SnO2 nanocrystals with cobalt doping and its effect on the optical properties.

    S. Roy, A. G. Joshi, S. Chatterjee and A. K. Ghosh, Nanoscale, 2018, Accepted Manuscript , DOI: 10.1039/C7NR07427A

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