ZnO nanocrystals were prepared from the decomposition of zinc(II) 2-ethylhexanoate. Soluble nanocrystals with a size ranging from about 5 to 8 nm were obtained. The powders obtained were tested as optical gas sensor based on photoluminescence (PL) variation with NO 2 , ethanol and relative humidity at room temperature (RT). The surface capping of the ZnO nanocrystals was modified by substituting the native dodecylamine capping with phosphorus or sulfur containing ligands, in order to investigate the effect of the surface chemistry onto the sensing properties. The reversible PL variations that we observed at RT are opposite to that reported in literature for ZnO, probably due to surface properties of the powders examined. We demonstrated that PL is increased by interaction with NO 2 at few ppm concentration and decreased upon interaction with reducing gases like ethanol. Further investigation on …