Dopant incorporation in ultrasmall quantum dots: a case study on the effect of dopant concentration on lattice and properties of SnO2 QDs

Although impurity doping of nanocrystals is essential in controlling their properties for various applications, but the doping mechanism of ultrasmall semiconductor QDs is not yet understood. In this study, the effect of concentration of Ni2+ ions on the lattice and properties of 1.4nm SnO2 QDs, prepared via chemical-precipitation route has been studied in detail. The quantum dot lattice contracted at maximum Ni concentration of 10% due to the incorporation of Ni ions at the substitutional sites on the surface of SnO2 lattice, while it began to expand gradually as the Ni concentration was further decreased from 10 to 1%, due in part to the Ni ions located in the core of the host lattice, occupying interstitial sites between Sn and O atoms leading to the expansion of the lattice with the decrease in the amount of strain and dislocation density. High resolution transmission electron microscopy confirms the presence of such dislocations in pure and doped SnO2 QDs. Optical investigation shows that the Ni doping in SnO2 lattice leads to a blue shift in the absorption wavelength. The concentration quenching effect of the PL emission with Ni doping is explained in detail. An enhancement in the photocatalytic activity has been achieved with optimum Ni incorporation in SnO2. The work also successfully correlates photoluminescence quenching and enhanced photocatalytic activity with the defect production happened in SnO2 system on Ni doping.