Organically-modified silica xerogels from 3-aminopropyltrimethoxysilane (APTES) and 3-isocyanatepropyltriethoxysilane (IMES) have been synthesized through carboxylic acid (formic acid, acetic acid and valeric acid) solvolysis. The resulting hybrid materials have been characterized by powder X-ray diffraction, mid-infrared spectroscopy, Si-29 and C-13 nuclear magnetic resonance, and photoluminescence spectroscopy. The results show that urea cross-links have been formed in these hybrids. The luminescence features depend on the selected carboxylic acids. For example, comparatively to the hybrids derived from formic and acetic acid solvolysis, valeric acid shows a red-shift of the emission features.