Carbon nanodots (CNDs) have emerged as fascinating materials with exceptional electronic and optical properties, and thus they offer promising applications in photonics, photovoltaics and photocatalysis. Herein we study the optical properties and electron dynamics in CNDs using steady state and time-resolved spectroscopy. The photoluminescence (PL) is determined to originate from both core and surface. The massive surface fluorophores result in a broad spectral fluorescence. In addition to various synthesis techniques, it is demonstrated that the PL of CNDs can be extended from the blue to the near infrared by thermal assisted growth. Directional electron transfer was observed as fast as femtosecond in CND-graphene oxide nanocomposites from CND into graphene oxide. These results suggest CNDs can be promising in many applications.