Preparation of luminescent ZnO nanoparticles modified with aminopropyltriethoxy silane for optoelectronic applications

Highly luminescent ZnO nanoparticles have been synthesized through a co-precipitation method, starting from a solution of zinc acetate in methanol and precipitating the oxide phase in basic media in the presence of variable amounts of aminopropyltriethoxy silane (APTS). The adopted conditions led to the condensation between Zn-OH species and the alkoxy functionalities of the organosilane during the formation of nanoparticles (one-pot method) thus allowing covalent binding of organic functionalities on the ZnO surface. HR-TEM measurements indicated that samples synthesized with increasing concentration of APTS (from 1 to 10% of Si/Zn molar ratio) are made of ZnO nanoparticles of decreasing dimension, passing from ca. 6 nm for pure ZnO to ca. 3 nm for the ZnO functionalized with the highest organosilane loading. ZnO samples with reduced particle size showed a significant variation of the optical properties. In particular, the particle size reduction is associated with a significant modification of ZnO absorption properties, as studied by diffuse reflectance UV-Vis spectroscopy, and to an exceedingly high photoemission. The organo-modified ZnO nanopowder with the highest photoemission was successfully tested as a light-emitting layer in a new generation of LED devices thus proving that they also possess interesting electroluminescent properties.