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 Sn sub(1-x)Mn sub(x)O (0 less than or equal to x less than or equal to 0.05) nanoparticles. In addition, an effort was made to understand the effect of Mn doping on the structural and optical properties of SnO sub(2). X-ray diffraction analysis showed a tetragonal structure and the unit cell volume decreased slightly with Mn super(4+) content. The Mn:SnO sub(2) 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 Mn super(4+) ions occupying the lattice sites of Sn super(4+) in the SnO sub(2) host. Electron energy loss spectroscopy further confirmed composition and oxidation states of Sn super(4+) and Mn super(4+) ions. Manganese doping increased the band gap of SnO sub(2) from 4 eV to 4.40 eV with Mn super(4+) concentration. Variation in band gap energy was attributed to the increasing lattice strain with Mn content and the charge transfer transitions between Mn super(4+) ions and conduction/valence bands of SnO sub(2). Three photoluminescence emission bands observed at 320, 360 and 380 nm, when excited at 250 nm, proved Mn:SnO sub(2) to exhibit good optical emission and to have potential application in nanoscale optoelectronic devices.