Crystal lattice spacing shrinkage and band-gap narrowing phenomena in In-doped SnO₂ nanoparticles

Pure and In-doped Tin Oxide (SnO₂) nanoparticles with different doping concentration were prepared by hydrothermal method. The prepared samples were characterized by XRD, TEM, and UV–vis absorption spectroscopy. The crystal lattice spacing $d$ of In-doped SnO₂ nanoparticles decreases compared with pure SnO₂. The crystal lattice spacing ratios $\Delta d/d$ for (110), (101) and (211) crystal face shrinks acutely with 1.9% doping in SnO₂. Crystallite size calculated by the FWHM of the first major XRD peaks (110) decreases from 3.945 to 3.281 nm as the doping concentration increases from 0 to 10%, whereas the strain increases. XRD study reveals that crystal lattice spacing of SnO₂ nanoparticles shrinks due to the effect of In element doping. Optical band-gap of SnO₂ nanoparticles decreases from 3.76 to 3.33 eV first, and then increases to 3.55 and 3.52 eV, respectively, as the doping concentration changes from 1.9, 3.8 to 10%. Band-gap narrowing originates from the effect of crystal lattice spacing shrinkage. (paper)