How porosity affects the emission of fluorescent carbon dot-silica porous composites

Blue-emitting nitrogen-doped carbon dots (CDN) produced by a solvent-free method have been successfully incorporated into silica (SiO2) through a sol-gel procedure. By exploiting the co-gelation of the dispersed carbon dots and of the silica matrix, homogeneous distribution of the carbon dots was obtained throughout the matrix. The CDN-SiO2 composites in the form of xero-, cryo-, and aerogels featuring different porous textures were produced by exploiting different gel drying strategies. The most critical parameters and the material features associated to the different synthesis were investigated by transmission electron microscopy, thermal analysis, Mid-infrared spectroscopy, N-2 physisorption isotherms and time-resolved spectrofluorimetry. The emissive properties of CDN-SiO2 composites in the form of aero-, cryo- and xerogel were studied. The spectral properties and the efficiency of the emission change in the CDN-SiO2 composites pointed at the effect of CD loading and porous texture of xerogels. Our investigation expands the exploitation of functional carbon dots through the production of fluorescent solid-state composites with tunable porosities.