Hot Carrier Cooling and Multiphoton Absorption of Quasi-Type II ZnSeTe-Based Quantum Dots

Ternary ZnSeTe quantum dots (QDs) are regarded as the most promising Cd-free blue emitters, while their fundamental optical properties such as hot carrier (HC) cooling process and multiphoton absorption (MPA) remain unclear, which will hinder their potential application. In this work, we compare the HC cooling processes of ZnSeTe/ZnSeS and ZnSeTe/ZnSeS/ZnS QDs and find that the HC cooling times of ZnSeTe/ZnSeS/ZnS QDs are insensitive to excitation intensity as a result of the suppressed hot-phonon bottleneck and Auger effect. Importantly, we have determined the two- to five-photon absorption cross sections of two kinds of QDs, highlighting the advantages of ZnS shells in enhancing MPA cross sections of ZnSeTe-based QDs. These insightful findings shed light on the underlying optical properties of ZnSeTe-based QDs and emphasize the critical role of the shell in engineering their HC cooling and MPA performance.