Recently, the biomass "bottom-up" approach for the synthesis of graphene quantum dots (GQDs) has attracted broad interest because of the outstanding features, including low-cost, rapid, and environmentally friendly nature. However, the low crystalline quality of products, substitutional doping with heteroatoms in lattice, and ambiguous reaction mechanism strongly challenge the further development of this technique. Herein, we proposed a facile and effective strategy to prepare controllable sulfur (S) doping in GQDs, occurring in a lattice substitution manner, by hydrothermal treatment of durian with platinum catalyst. S atoms in GQDs are demonstrated to exist in the thiophene structure, resulting in good optical and chemical stabilities, as well as ultrahigh quantum yield. Detailed mechanism of the hydrothermal reaction progress was investigated. High-efficiency reforming cyclization provided by platinum was evidenced by the coexistence of diversified sp-fused heterocyclic compounds and thiophene derivatives. Moreover, we also demonstrated that saccharides in durian with small molecular weight (<1000 Da) is the main carbon source for the forming GQDs. Because of the desulfurizing process, controllable photoluminescence properties could be achieved in the as-prepared GQDs via tuning doping concentrations.

Carbon‐based quantum dots (CQDs), including spherical carbon dots and graphene quantum dots, are an emerging class of photoluminescent (PL) materials with unique properties. Great progress has been made in the design and fabrication of high‐performance CQDs, however, the challenge of developing solid‐state PL CQDs have aroused great interest among researchers. A clear PL mechanism is the basis for the development of high‐performance solid‐state CQDs for light emission and is also a prerequisite for the realization of multiple practical applications. However, the extremely complex structure of a CQD greatly limits the understanding of the solid‐state PL mechanism of CQDs. So far, a variety of models have been proposed to explain the PL of solid‐state CQDs, but they have not been unified. This review summarizes the current understanding of the solid‐state PL of solid‐state CQDs from the perspective of energy band theory and electronic transitions. In addition, the common strategies for realizing solid‐state PL in CQDs are also summarized. Furthermore, the applications of CQDs in the fields of light‐emitting devices, anti‐counterfeiting, fingerprint detection, etc., are proposed. Finally, a brief outlook is given, highlighting current problems, and directions for development of solid‐state PL of CQDs.