Properties of Luminescent Si Nanoparticles in Sol-Gel Matrices

In this wor e preparation and properties of silica sol-gels incorporating luminescent Si nanocrystallites extracted from porous Si are described for the first time. These sol-gel/Si nanocrystallite composite materials are characterized by BET isotherm measurements, photoluminescence spectroscopy, and infrared spectroscopy. To stabilize the photoluminescence (PL) of Si crystallites within the silica matrix, a fatty acid (capric (C₁₀), myristic (C₁₄) or arachidic acid (C₂₀)) is added as a passivation agent during the hydrolysis of tetraethoxysilane. The presence of the fatty acid is crucial to the long-term stability of the Si nanocrystallite luminescence, as the Si visible light emission remains essentially unchanged for more than a month when the fatty acid is present in the mixture but degrades quickly (within days) when absent. The thermal stability of the Si luminescence within the sol-gel is also reported. Fluorescence microscopy reveals that the light-emitting Si crystallites aggregate into micron-sized domains somewhat unevenly throughout the silica matrix. This distribution of Si crystallites can be improved by employing a surfactant, dioctyl sodium sulfosuccinate (DSS).