Instead of using traditional external heating treatment methods, a facile heating equipment-free method is developed for one-pot synthesis of fluorescent carbon dots (CDs) via exothermic crosslinking reaction enabled “self-heating” and further induced high degree of carbonization. The obtained CDs exhibit strong blue fluorescence and are well characterized through a series of advanced analysis, including their optical properties, surface morphology, and chemical compositions. The corresponding synthesis mechanism is also disscussed and proposed. Moreover, the as-synthesized carbon dots have been successfully applied for selective Fe3+ detection as a simple demonstration. Fe3+ can significantly quench the fluorescence signal of CDs, whereas other metal ions show insignificant effect on their fluorescence intensity. The quenching performance is ascribed to synergistic effect of electrostatic interaction between ferric ions and the fluorescent CDs as well as interaction induced electron transfer. This study expands the cutting edge of simple synthesis of fluorescent CDs, where CDs hold great promises in sensing applications.