Zn/F-doped tin oxide nanoparticles synthesized by laser pyrolysis: structural and optical properties

Zn/F co-doped SnO₂ nanoparticles with a mean diameter of less than 15 nm and a narrow size distribution were synthesized by a one-step laser pyrolysis technique using a reactive mixture containing tetramethyltin (SnMe₄) and diethylzinc (ZnEt₂) vapors, diluted Ar, O₂ and SF₆. Their structural, morphological, optical and electrical properties are reported in this work. The X-ray diffraction (XRD) analysis shows that the nanoparticles possess a tetragonal SnO₂ crystalline structure. The main diffraction patterns of stannous fluoride (SnF₂) were also identified and a reduction in intensity with increasing Zn percentage was evidenced. For the elemental composition estimation, energy dispersion X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) measurements were performed. In general, both analyses showed that the Zn percentage increases with increasing ZnEt₂ flow, accompanied at the same time by a decrease in the amount of F in the nanopowders when the same SF₆ flow was employed. The Raman spectra of the nanoparticles show the influence of both Zn and F content and crystallite size. The fluorine presence is due to the catalytic partial decomposition of the SF₆ laser energy transfer agent. In direct correlation with the increase in the Zn doping level, the bandgap of co-doped nanoparticles shifts to lower energy (from 3.55 to 2.88 eV for the highest Zn dopant concentration).