Advanced applications of porous silicon: Biofunctionalized luminescent particles and ZnO based white light emitting nanocomposites

Resumen

Porous silicon (PS) is a material with special properties. Its most relevant characteristic is the efficient photoluminescence at room temperature caused by quantum confinement, but not less attractive are its biocompatibility and high surface to volume ratio. All these properties make this material especially suitable for biomedical and optoelectronic applications and thus, the present study aims at deepening in PS conditioning towards applications in these fields. On the one hand, the functionalization of luminescent PS particles has been studied for possible biomedical applications by two different ways: silanization (using 3-Aminopropyltriethoxysilane) and pegilation (using polyethylene-glycol). Both molecules have attractive properties: the former has amino capping groups (-NH2) capable of linking biomolecules such proteins or DNA to the particles, while the latter (with two hydroxyl (-OH) ending groups), makes the particles more soluble in aqueous media. The synthesis and full colloidal and surface characterization has been achieved, showing that PS is conveniently conjugated forming particles in the micron range. In addition, it has been considered how functionalization protects the particles from oxidation, preserving their luminescence for longer time with respect to pristine PS particles. On the other hand, new applications of PS are envisaged by a proper combination with zinc oxide (ZnO) to produce ZnO-PS nanocomposites. The structures where grown by combining the electrochemical anodization of Si with a sol-gel process for permeation of the formed PS with ZnO. Intermediate annealing temperatures have been optimized to crystallize the ZnO nanoclusters, making these compatible with the presence of Si quantum dots within PS. More specifically, this work is focused in the existent correlation between luminescence and the PS-ZnO fine structure after sample annealing at different temperatures in air. The luminescence changes allows us to tune the emission and form white light electroluminescent devices based exclusively on PS and ZnO. Furthermore, the lack of a model that explains the electrical behavior and the mechanism of white-light emission from these structures moved us to propose one.