Photoluminescence Intensity Fluctuations and Temperature-Dependent Decay Dynamics of Individual Carbon Nanotube sp Defects.

Recent demonstration of room temperature, telecommunication wavelength single photon generation by sp defects of single wall carbon nanotubes established these defects as a new class of quantum materials. However, their practical utilization in development of quantum light sources calls for a significant improvement in their imperfect quantum yield (QY∼10-30%). PL intensity fluctuations observed with some defects also need to be eliminated. Aiming toward attaining fundamental understanding necessary for addressing these critical issues, we investigate PL intensity fluctuation and PL decay dynamics of aryl sp defects of (6,5), (7,5), and (10,3) single wall carbon nanotubes (SWCNTs) at temperatures ranging from 300 to 4 K. By correlating defect-state PL intensity fluctuations with change (or lack of change) in PL decay dynamics, we identified random variations in the trapping efficiency of E band-edge excitons (likely resulting from the existence of a fluctuating potential barrier in the vicinity of the defect) as the mechanism mainly responsible for the defect PL intensity fluctuations. Furthermore, by analyzing the temperature dependence of PL intensity and decay dynamics of individual defects based on a kinetic model involving the trapping and detrapping of excitons by optically allowed and forbidden (bright and dark) defect states, we estimate the height of the potential barrier to be in the 3-22 meV range. Our analysis also provides further confirmation of recent DFT simulation results that the emissive sp defect state is accompanied by an energetically higher-lying optically forbidden (dark) exciton state.