Carbon nanodots (CND) have recently attracted tremendous attention for a variety of optical and optoelectronic applications. Although many attempts have been made to obtain high-quality CND in high yield, there have been few endeavors to regulate its energy structure. In this work, we have synthesized nitrogen-doped carbon nanodots (N-CND) through soft-template synthesis using citric acid and ethylenediamine (EDA) as carbon and nitrogen sources, respectively. The energy structure of N-CND has been modulated by regulating the concentration of EDA. A series of spectroscopic measurements showed that the absorption peak is developed near 370 nm and the photoluminescence peak is red-shifted with increasing nitrogen content. To utilize N-CND's strong near-UV absorption, broad-range visible-light emission, high quantum yield, and good organic compatibility, we have demonstrated phosphor-based light-emitting diodes employing N-CND as a phosphor.