Rhodamine B (RB) dimers were observed in doped gel glasses made by sol-gel processing in a wide range of dye concentrations. The photophysical properties such as excitation/fluorescence spectra and lifetimes of the studied doped gel glasses within a high dye concentration range are characteristic of adsorbed fluorescent J-dimers. To our knowledge, this is the first time that these species have been reported at the xerogel state of doped sol-gel glasses. The formation of fluorescent J-dimers rather than nonfluorescent PI-dimers has been studied and was attributed to the geometry that the dimers adopt upon adsorption on the silica gel surface. Geometry is also related to the specific concentration of RE molecules inside the pores. Through the study of the photophysical properties of the doped gel glasses, conversion from fluorescent J-dimers to nonfluorescent H-dimers was observed over a defined RE concentration range. The appearance of these fluorescent J-dimers, even at hi,oh dye concentrations, demonstrates the improved capability of these matrices to be used as solid dye lasers.