Influence of manganese ions in the band gap of tin oxide nanoparticles: structure, microstructure and optical studies

This paper presents the joint effect of strain-and doping-induced band gap change in Sn1-xMnxO (0 <= x <= 0.05) nanoparticles. In addition, an effort was made to understand the effect of Mn doping on the structural and optical properties of SnO2. X-ray diffraction analysis showed a tetragonal structure and the unit cell volume decreased slightly with Mn4+ content. The Mn: SnO2 are spherical shaped particles with a size ranging from 7.7 to 13.8 nm as calculated by transmission electron microscopy, Scherrer's formula and Willamson-Hall plot. X-ray photoelectron spectroscopy showed clear evidence for tetragonal coordinated high-spin Mn4+ ions occupying the lattice sites of Sn4+ in the SnO2 host. Electron energy loss spectroscopy further confirmed composition and oxidation states of Sn4+ and Mn4+ ions. Manganese doping increased the band gap of SnO2 from 4 eV to 4.40 eV with Mn4+ concentration. Variation in band gap energy was attributed to the increasing lattice strain with Mn content and the charge transfer transitions between Mn4+ ions and conduction/ valence bands of SnO2. Three photoluminescence emission bands observed at 320, 360 and 380 nm, when excited at 250 nm, proved Mn: SnO2 to exhibit good optical emission and to have potential application in nanoscale optoelectronic devices.