The Surface Plasmon Resonance Absorption of Indium Tin Oxide Nanoparticles and its Control

Indium tin oxide (ITO) nanoparticles (NPs) were prepared by a coprecipitation process from a mixed solution consisting of indium chloride and tin chloride. The surface plasmon resonance (SPR) absorption was studied under different calcinate atmospheres. The characteristics of the optical properties, especially the absorption of near-infrared (NIR) region was recorded by the UV-Vis-NIR absorption spectroscopy. The results show that the SPR absorption peak appears at 2500 nm under an oxidizing atmosphere (air) or at 1300 nm under a reducing atmosphere (a gas mixture of Ar and 5 vol% H2) when calcinated under a single atmosphere. There is no change in the plasmon frequency with the variance of calcinate temperatures and therefore no change in the free carrier concentration. However, when calcinated first at 600 °C under an oxidizing atmosphere and then reheated under a reducing atmosphere at different temperature, the SPR absorption peaks of the ITO NPs are at the range of from 1200 nm to 1430 nm, undergoing a blue shift as the reducing process temperature increases. The SPR absorption of the prepared ITO NPs is easily controlled by calcinate temperature under a process of calcination first under an oxidizing atmosphere and followed by under a reducing atmosphere.