Carbon quantum dots displaying dual-wavelength photoluminescence and electrochemiluminescence prepared by high-energy ball milling

Carbon quantum dots (CQDs) with multiple surface states were prepared by high-energy ball milling a mixture of activated carbon and KOH, followed by ultrafiltration purification. The as-prepared CQDs exhibit dual-wavelength photoluminescence emission peaks. Most interestingly, the first emission peak is independent of excitation wavelength (λex) and the second one is dependent on λex and red shifts monotonically with increasing λex. Meanwhile, the as-prepared CQDs also present dual-wavelength electrochemiluminescence property.