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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 ( λ ex ) and the second one is dependent on λ ex and red shifts monotonically with increasing λ ex . Meanwhile, the as-prepared CQDs also present dual-wavelength electrochemiluminescence property. [ABSTRACT FROM AUTHOR]