High-Order Multiphoton Emission and Lasing Enabled by Alloy Crown Passivation in CdSe/CdSeS Core/Crown Nanoplatelets

Colloidal CdSe semiconductor nanoplatelets (NPLs) are promising materials for nonlinear optoelectronic applications due to their tunable emission, large multiphoton absorption (MPA) cross section, and high optical gain. Although two- and three-photon pumped lasing has been reported for CdSe quantum dots and nanorods, realizing higher-order multiphoton emission, such as five-photon pumped lasers, remains a major challenge due to weak nonlinear absorption and rapid Auger recombination. Herein, five-photon pumped amplified spontaneous emission (ASE) and lasing in colloidal CdSe/CdSeS core/crown NPLs have been demonstrated. By systematically increasing the crown width, a significant enhancement in the MPA cross section and a corresponding reduction in ASE thresholds were observed, which were attributed to the CdSeS alloy crown coating. Furthermore, a vertical-cavity surface-emitting laser driven by five-photon excitation is experimentally demonstrated using core/crown NPLs. These findings provide a new approach for designing nonlinear optoelectronic materials and expand the potential of NPLs for deep-tissue bioimaging and high-order photonic devices.