A simple one-pot route to large-scale synthesis of ZnO nanoparticles (NPs) has been demonstrated, and the ZnO NPs can be produced more than 34 grams in one synthesis process. The ZnO NPs show bright yellowish fluorescence under ultraviolet illumination with a quantum yield (QY) of 42%, which make them suitable for application as phosphors in light-emitting devices (LEDs). Yellowish LEDs have been fabricated by employing the ZnO NP powder as phosphors, and the luminous efficiency of the LEDs can reach 64.2 lm/W. Additionally, the fluorescence intensity of the phosphors shows little degradation when the ambient temperature reaches 100 °C, and the correlated color temperature of the LEDs remains constant when the driving current reaches 100 mA, indicating the good temperature and injection-current stability of the ZnO NP phosphors.