Infrared absorptive properties of Al-doped ZnO divided powder

Al-doped ZnO powders were synthesised by a Pechini process in order to obtain visible non-absorbent and near-Infrared absorbent particles. Firstly, it has been shown that synthesis under argon combined with the lowest synthesis temperatures (700 °C) allows getting the optimal properties for pure ZnO compounds due to creation of n-type defects segregated on oxide grain surface (Zn/O ratio superior to 1). Nevertheless, the near-Infrared absorption properties of the pure ZnO compounds remain low. The Al3+ doping of ZnO compounds was then investigated. The Al solubility limit inside ZnO doped compounds decreases drastically with the grain size, i.e. with the synthesis temperature. Then, the Al cations distribution varies inside ZnO grains, Al3+ segregation at the grain surfaces taking place for high synthesis temperatures. The optimal optical properties (high near-Infrared absorption) are reached combining Al-doping and adequate synthesis conditions: annealing under argon at low temperatures. In these conditions, the highest extrinsic (via Al doping) and intrinsic n-types defects rates are indeed reached.