Ultrafast Charge Carrier Dynamics and Nonlinear Optical Absorption of InP/ZnS Core-Shell Colloidal Quantum Dots

Understanding of ultrafast carrier dynamics in InP/ZnS colloidal quantum dots (QDs) is essential for their optoelectronic applications. In this paper, we have successfully fabricated high-quality InP/ZnS core-shell QDs with quantum yield (QY) of 47%. Time-resolved photoluminescence (TRPL) and femtosecond transient absorption (TAS) measurements were performed to characterize the carrier injection, relaxation, and transition process in the InP/ZnS QDs. It is found that the photoexcited carrier first injected to the ZnS shell in 2 ps, then relaxed to the alloyed layer between the ZnS shell and InP core in 7.4 ps, next relaxed to different energy levels in the InP core in about 170 ps, and finally recombined by charged and neutral excitons transition in 4.1 and 26.7 ns, respectively. Additionally, the two-photon absorption (TPA) coefficient obtained from Z-scan measurement indicates that InP/ZnS QDs possess good nonlinearly optical properties. Our research is significant for the improvement and engineering of InP/ZnS QDs-based materials for optoelectronic applications.