Electrochemical control of emission enhancement in solid-state nitrogen-doped carbon quantum dots

Abstract

Because of their excellent optical and electrical properties, doped carbon quantum dots (CQDs) are expected to be used in novel film optoelectronic devices such as light-emitting diodes and solar cells. However, these device advancements are currently hindered by the elusive photophysical process of doped CQDs in solid-state films. Here, the optical properties of nitrogen-doped CQD (N-CQD) films are studied using spectro-electrochemical (SEC) methods. A distinctive photoluminescence (PL) enhancement phenomenon is observed, in which the PL intensity of the N-CQD film can be increased in both positive and negative electrochemical potential sweeps. The effect of positive potential on PL enhancement is greater (∼340% at +1.4 V), while that of negative potential is slightly weaker (∼10% at −1.4 V). To the best of our knowledge, no similar brightening process has been reported in all previous SEC studies on a variety of QDs, wherein the emission intensity can only exhibit enhancement under positive or negative potential at most. We propose that the above PL brightening is related to the weakened π–π stacking effect after electrochemical charge injection and nitrogen doping plays a crucial role in it. Finally, a low hysteresis reversible electrochemistry regulation of the PL spectrum can be achieved by increasing electrolyte fluidity with argon gas bubbling to reduce local charge aggregation.