Anion doped binary oxides, SnO₂, TiO₂ and ZnO: Fabrication procedures, fascinating properties and future prospects

Abstract

Doping the oxygen in the three technologically important binary oxides SnO₂, TiO₂, and ZnO, with other anions such as nitrogen, carbon, fluorine, sulfur and chlorine by various synthetic procedures are described. The crystal structures of these oxides along with their electronic structures are summarized. The evolution of many useful properties, such as efficient photocatalysis, high electrical conductivity with high optical transparency on doping with some of these anions, is discussed. An important milestone achieved by our research group for the synthesis of F-doped SnO₂ and ZnO powders is highlighted. Heavily F-doped SnO₂, obtained by the safe, simple, reliable and reproducible synthetic approach developed by us is the first example among oxide semiconductors to show Moss-Burstein effect, and consequently the defect states are produced in the system on injection of extra charge carriers. These trapped defect states give rise to glow curves in the thermoluminescence spectrum. This observation suggests the use of SnO₂:F as a thermal UV sensors in high radiation environments. In the concluding part, the need for the investigation in to the interesting structural, electronic and optical properties, especially in the heavily doped regime, are portrayed as part of the future directions of research in these oxides.