Coke is a by-product of coal. This paper reports a simple and green chemical oxidation method for carbon quantum dots (CQDs) from coke for use in novel applications. The CQDs emit blue fluorescence and have a fluorescence quantum yield of 9.2% and blue-green-red spectral composition of 48%. A light-emitting diode (LED) was fabricated by combining the CQDs as a white-light converter with an ultraviolet chip. The Commission Internationale de L'Eclairage chromaticity coordinate (0.31, 0.35) and correlated color temperature (5125 K) of the LED are located in a cool white light zone, suggesting that they have superior potential application in lighting devices.