We report herein the synthesis of carbogenic dots (CDs) by a one-step pyrolysis from N-acetylcysteine. The as-prepared CDs show excellent dispersibility with particle sizes in the range of 3-5 nm. Under stimulation with blue light, the CDs emit broad yellow fluorescence, which is still rarely reported by now. The optical properties were throughly investigated, and we found the CDs exhibit stable fluorescence, high quantum yield, and pH dependence. Moreover, an economical approach for constructing white light-emitting diodes (LEDs) was developed by combining the yellow-emitting CDs with blue GaN-based LED chips. The white LEDs exhibit warm white light with the color coordinates of (0.34, 0.35), very close to the coordinates of balanced white-light emission (0.33, 0.33). These results suggest that the CDs can be a promising candidate as yellow-emitting phosphor for white LEDs.