Synthesis of sol-gel SiO2-based materials using alkoxydisilane precursors: mechanisms and luminescence studies

This work reports on the mechanisms behind the sol-gel synthesis and versatile luminescent behavior of sol-gel silica-based materials based on hexamethoxydisilane (Hexamet) or hexaethoxydisilane (Hexaet) innocuous monomers, at different annealing temperatures. The resulting as-synthesized materials exhibit an intense photoluminescence (PL) band in the blue region of the spectrum, whose maximum shifted in the region of 430-650 nm by applying an annealing process at different temperatures in the range of 350-1,000 A degrees C. This behavior could be attributed to the presence of different silica matrix defect-related luminescent mechanisms. PL emission bands of the Hexamet-derived materials prepared at higher T up to 1,300 A degrees C slightly shifted and appeared in the region of 400-700 nm. However, those Hexaet-derived materials annealed at T between 1,000-1,150 A degrees C showed bands peaking at and above 800 nm, these being related to a quantum confinement effect induced by the presence of silicon nanocrystals (Si_nc) within the polymer matrix. Based on studies carried out by different microscopy and chemical analysis techniques, the origin of the PL behavior was attributed to the kinetics of the hydrolysis and condensation reactions being different for each monomer, which generate different intermediates and eventual structures during the annealing process. The superior tunable luminescent performance of these environmentally-friendly materials provides them with the potential for the fabrication of silicon-based light sources. The superior luminescent performance of SiO2-based materials synthesized by a simple sol-gel process using two different disilane monomers was tuned in a wavelength range from 430 to 860 nm. The mechanisms that appear to govern both the material synthesis and luminescent behaviour are thoroughly described based on results gathered by spectroscopy, microscopy and chemical analyses.