Quantum confinement effects and band gap engineering of SnO2 nanocrystals in a MgO matrix Original Research Article

Nanocrystal formation of SnO2 in xSnO2–(100 − x)MgO (x in mol.%) nanocrystalline composite thin films is reported. SnO2 and MgO exhibit strong immiscibility behavior below 750 °C, leading to controllable particle size of SnO2 in the MgO matrix by changing their composition. The particle size of SnO2 can also be controlled by increasing the annealing temperature. Above 750 °C MgO and SnO2 react to yield a MgO–Mg2SnO4–SnO2 composite in which the size of the SnO2 nanophase increases with increasing temperature. By controlled choice of the composition and annealing conditions the band gap of SnO2 can be continuously increased from 3.89 to 4.5 eV. We discuss this behavior in terms of the quantum confinement effect. The method provides a generic approach to tuning the band gap in nanocomposite systems over a wide energy range.