Electrochemistry and electrochemiluminescence ( ECL) have been applied to study the blue luminescent carbon nanocrystals ( NCs). It is found that electrons can be injected into the NCs in sequence. This observation suggests that carbon NCs can stably store charge in solution. The positively charged NCs were found to be more stable than the negatively charged NCs. The red shifted ECL ( relative to photoluminescence) suggests that the ECL emission from carbon NCs originates from surface traps. (C) 2010 Elsevier B. V. All rights reserved.