“…[213] CQDs have outstanding features such as low cost, easy synthesis, excellent biocompatibility, and photoluminescence. [212] The absorption and emission spectra of CQDs can be tuned by adjusting the precursor type, preparation method, degree of carbonization, surface state, and element doping. [214] In addition, CQDs have abundant functional groups, such as hydroxyl, amino, and carboxyl groups, which are easy to be modified.…”