Photoluminescence-tunable carbon nanodots: Surface-state energy-gap tuning

A controllable wet oxidation method for synthesizing excitation-independent C-dots with tunable fluorescent colors was developed. carbon fibers (CFs) were added to a nitric acid solution. Then, the well-stirred solution was heated to 120°C and refluxed for 48 h. The corresponding solution containing C-dots was collected at a given time and then neutralized with NaOH. The resulting solution was first filtered by membrane filters and then ultrafiltered successively. The ECL experiments were conducted in a three-electrode electrochemical system with a Pt-disk working electrode, a Pt-wire counter electrode, and an Ag/AgCl reference electrode. The results revealed that the PL properties of C-dots, mainly influenced by their size and degree of surface oxidation, can be tuned by varying reaction time, temperature, and concentration of nitric acid. The energy gap of the surface states, where electrons and holes recombine to emit fluorescence, correlated with the extent of the π-electron system and surface chemistry.