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

Abstract Nanocrystal formation of SnO 2 in x SnO 2 –(100 − x )MgO ( x in mol.%) nanocrystalline composite thin films is reported. SnO 2 and MgO exhibit strong immiscibility behavior below 750 °C, leading to controllable particle size of SnO 2 in the MgO matrix by changing their composition. The particle size of SnO 2 can also be controlled by increasing the annealing temperature. Above 750 °C MgO and SnO 2 react to yield a MgO–Mg 2 SnO 4 –SnO 2 composite in which the size of the SnO 2 nanophase increases with increasing temperature. By controlled choice of the composition and annealing conditions the band gap of SnO 2 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.