Solid State Phosoluminescence Of Carbon Dots And The Mechanism

Carbon dots are a kind of newly discovered nanolight with potentially highquantum yield. They are composed of two components. They have cores ofcrystallized or amorphous sp2hybridized carbon. They have surfaces that arefunctionalized by various functional groups, such as hydroxyl, carboxyl, carbonyland ammonia. They are stable, biocompatible, their raw materials (graphite orcarbohydrate) are widely available and their preparation methods are usually facile.They have attracted increasing interests in recent years. Most works reported so farfocused on their fluorescence on biomedical applications such as bio-imaging andchemical sensing, where they are stored in aqueous systems and theirphotoluminescence is in aqueous environments. To explore the possibility ofelectroluminescence from carbon dots in solid state, we need firstly to study thephotoluminescence of carbon dots in solid state. However, works on this area arerare. Therefore, it became our main project of research. We have done the followingworks:1We have developed the preparation and purification of carbon dots. Weprepared carbon dots by pyrolysis of EDTA-2Na or EDTA under400℃in N2atmosphere in a tube furnace and then purifying the product by acetone through thesize-selective deposition process. Blue fluorescent carbon dots in aqueous systemwere then obtained.2We studied the photoluminescence of carbon dots in solid state. We found that their photoluminescence is dependent on substrates. The blue emission was oftenquenched in most cases, but was recovered on hydrophilic substrates. A mechanismis proposed based on structural and spectral characterization as well as theory ofmolecular fluorescence and related reports. Based on the mechanism, we discussedthe possibility of carbon dots based electroluminescent devices and proposed waysto realize them.3We found for the first time pure organic room temperature phosphorescencefrom carbon dots based composite films (such as carbon dots/polyvinyl alcohol(PVA)). An explanation was proposed based on spectral investigations and relatedreports. We have demonstrated the concept of using such room temperaturephosphorescence for anti-counterfeiting features.