Synthesis of luminescent glass monoliths embedding water-soluble Carbon dots

Carbon dots (CD) are an emerging class of nanomaterials, currently motivating an intense scientific interest because of their bright and characteristically tunable fluorescence, and their possible applications such as sensors, lasers, imaging agents, white light emitting devices [1]. While most studies focused on CDs in liquid phase, a strong effort is being recently devoted to produce fluorescent solids embedding highly dispersed CDs. Many of these procedures are elaborate and require pre-functionalization of the dots [2]. Here we report a novel and very facile route to prepare glass monoliths containing CDs with no need of pre-functionalization of the dots. Our low-cost synthesis method produces solids with high optical quality preserving the fascinating luminescence properties of CDs. We prepared CDs from an aqueous solution of citric acid monohydrate and urea, which was boiled up to the complete evaporation of water, yielding a black powder which was dried in vacuum at room temperature for 90 minutes. The obtained sample is highly soluble in polar solvents, especially water (up to at least 15 gL-1), these solutions being stable and highly fluorescent under near-UV or visible light. CDs were characterized via atomic force microscopy, thus obtaining the statistical distribution of heights (Figure 1). The resulting typical size of CDs (