Investigating the Pump Fluence and Mn Doping Dependence in Biexciton Generation in CdTe QDs and Their Dynamics through Transient Absorption Spectroscopy

Water-soluble CdTe quantum dots (QDs) are systematically synthesized to study the influence of Mn dopant on charge-carrier dynamics under different pump excitation fluences. Herein, we have introduced Mn dopant to manipulate the defect states in CdTe QDs and analyzed its effect on biexciton as well as hot electron dynamics. The optical studies evidently support the presence of Mn dopant energy states above the conduction band edge of the CdTe QDs. From the transient absorption analysis, the band edge bleach growth time and the early time band edge bleach position in the high-energy region to the absorption band edge portion, under higher exciton occupancy per QD, reveal the biexciton generation processes and the hot electron relaxation process in Mn-CdTe QDs. The kinetics at the band edge bleach along with the positive transient absorption spectral slice in QDs further explain the relaxation mechanism of hot charge carriers to the lower energy level. Interestingly, we obtained increases in biexciton binding energy and a suppressed hot electron cooling time in the presence of Mn dopant in CdTe QDs at fluence excitation.