Carbon dots' unusual optoelectronic properties in silica aerogels.

The unique properties that aerogels exhibit have been the main reason for the intense research around new synthesis routes and new applications in various fields in recent years. Composite aerogels combine the properties of both the aerogel matrix and the inclusions, where the latter can be several materials in various forms. Carbon dots are suitable candidates to use as inclusion for the development of composite aerogels and that is due to their low-cost production, low toxicity, biocompatibility, and tunable fluorescence. Here we report the synthesis of a composite silica matrix aerogel with boron-doped carbon dots inclusions, and we focus on the optical response of the material. The method we use to prepare the composite aerogel is the classical sol-gel process using tetraethyl orthosilicate as silica precursor, followed by CO₂ supercritical drying. The resulting aerogel is crack-free, exhibiting a surface area of 518 m²/g and diverse optoelectronic properties compared to the pristine carbon dots in solution, as an excitation-dependent emission and an unusual blue-shift for excitation centered in the UVB region. The unfamiliar optoelectronic properties of the carbon dots in the aerogel are discussed and are attributed to the influence of the silica matrix. Hence, the induced carbon dots' aggregation may lead to recombination de-excitation pathways, whereas the photoluminescence contribution by the core-related de-excitation pathway may shorten, as the penetration depth of radiation into the dots' core may be affected by its intensity which drops drastically for high energies (for λ_exc. < 300 nm) due to strong absorption by the silica matrix. Highlights: Crack-free composite silica aerogels with photoluminescent carbon dots inclusions. Composite aerogels preserve their porous character with specific surface areas above 500 m²/g. Diverse optoelectronic properties compared to the pristine carbon dots in solution. Excitation-dependent emission and unusual blue-shift for excitation centered in the UVB region. The observations are attributed to several factors linked to the silica matrix. [ABSTRACT FROM AUTHOR]