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

Abstract

This paper presents the joint effect of strain- and doping-induced band gap change in Sn_1−xMn_xO (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.