Influence of Fe-doping on the structural and photoluminescence properties and on the band-gap narrowing of SnO2 nanoparticles

Abstract

In this study the structural and optical properties of Fe-doped SnO2 (Sn1-xFexO2, for x = 0, 0.03, 0.05, 0.07) nanoparticles synthesized by co-precipitation technique and using short durations of sample sintering is reported. The prepared samples are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Thermogravimetric analysis – differential scanning calorimetry (TG-DSC), UV–Visible spectroscopy (UV-VIS) and Photoluminescence (PL) measurements. The Rietveld refined XRD data shows that all the samples are in tetragonal rutile crystalline phase. Fe doping in the samples hinder grain growth as the average crystallite size (ranging in between 13 and 29 nm) reduces with doping concentration. Information on the phase purity of the samples is obtained via the FTIR and Raman measurements while the Thermogravimetric–Differential Scanning Calorimetric (TG-DSC) studies give an idea on the crystallization process of and the presence of oxygen vacancies in the samples. The finger print wave number region of rutile phase of SnO2 corresponds to the A1g mode, which shows a red shift in the Raman studies undertaken. This is indicative of the effect of the defects arising due to the dopant introduced, which affects the crystallite size and leads to phonon confinement, observed as the red shift of the Raman peaks. The addition of Fe leads to a band-gap narrowing process due to the d – d transition and a feeble absorption occurs in the near infrared region. The Photoluminescence (PL) curve shows a broad and intense emission in the UV region, near ~ 375 nm (3.31 eV), owing to the presence of oxygen vacancies. Apart from this, two additional feeble emission peaks for the 5% and 7% Fe-doped samples also evolve. The substitution of Fe, existing in the Fe2+/Fe3+ state, in place of Sn, existing in the Sn4+ state, gives rise to a charge/oxidation state imbalance. This creates a vacancy in the crystal, which acts as the emission center in the doped semiconductor type SnO2. The PL studies confirm the existence of Fe induced inter bands in the energy band-gap of these samples. The CIE chromaticity diagram shows that the prepared materials are suitable and tunable for blue light LED applications.