Experimental Studies on Blinking Behavior of Single InP/ZnS Quantum Dots: Effects of Synthetic Conditions and UV Irradiation

In this study, we first synthesized a series of highly fluorescent InP/ZnS core/shell QDs under varied reaction conditions and then systematically investigated the blinking behaviors of QDs by single molecule imaging technique. In the measurement of blinking processes, the PL intensity trajectories of single QDs with different emission peak were recorded by a total internal reflection fluorescence (TIRF) imaging system. We observed that particle size, molar ratio of myristic acid/indium (MA:In), and the overcoating of ZnS shell had significant influence on the blinking behaviors of InP/ZnS QDs. Statistical analysis documented that both the on and off events (m(on) and m(off)) followed the power-law distributions P(t(on/off)) = Bt(-mon/off), and the values for m(on) and m(off) were in the ranges of 1.3-1.7 and 1.4-1.9, respectively. As the wavelength of emission peak increased from 565 to 646 nm, the on-time fraction changed from 30% to 70%. The QDs prepared under higher MA/In ratio possessed a longer on-time fraction. The optimal overcoating time of the ZnS shell was about 3 h for blinking suppression in this case. Furthermore, we found that UV irradiation of QDs certainly suppressed the off-time fraction by reducing surface traps. We were able to control the blinking behavior of QDs by varying the synthesis parameters, and prepared InP/ZnS QDs with the on-time fraction up to 80% for future biological and photoelectric applications.