Fluorescent carbon dots in solid-state: From nanostructures to functional devices

In recent years, carbon dots (CDs) have attracted considerable attention for their potential application in photonics and optoelectronics. One of the main limitations in realizing efficient and reliable solid-state devices is the aggregation-caused quenching effect. At a short distance, the mutual interaction among nanoparticles enhances the non-radiative mechanisms, undermining the extraordinary optical properties of CDs. In this review, we have critically analyzed the main strategies for maintaining and empowering the optical properties of CDs from liquid to solid-state. These routes include the preparation of self-quenching-resistant fluorescent CDs and the embedding into different matrices. The material processing and the nature of the chemical environment surrounding the CDs are key parameters for selecting an optically transparent matrix. An optimized host material would preserve the fundamental properties of CDs, but also improve their performances extending the application field. Many types of matrices for CDs have been tested, such as polymers, organic-inorganic hybrid materials, mesoporous and layered materials. Besides, unconventional host materials have also used as a matrix, e.g. acid molecules condensates and inorganic salts. The successful use of CDs is highly relying on their incorporation into a solid-state matrix.