Complete Lateral Surface Passivation and Photostability Investigation of CdSe/CdSeS Core/Crown Nanoplatelets

The surface passivation of quasi-two-dimensional CdSe nanoplatelets (NPLs) is crucial for increasing their application potential in optoelectronic devices. While previous methods mainly focused on the passivation of vertical surfaces, effective passivation of lateral surface defects remains challenging. Herein, quasi-symmetric CdSe/CdSeS core/crown NPLs have been successfully synthesized, achieving complete lateral surface passivation through a uniform CdSeS crown. Laser spectroscopic analysis revealed that these CdSe/CdSeS core/crown NPLs exhibited a near-unity (98.89%) photoluminescence (PL) quantum yield with single-exponential PL decay dynamics. Furthermore, the dual effects of prolonged laser irradiation on NPLs have been observed, namely, the PL enhancement due to the photothermal passivation of cadmium vacancies and PL quenching caused by the new formation of cadmium vacancies through photoinduced ligand dissociation. Then, low-threshold whispering gallery mode microlasers were constructed with a SiO₂ microsphere. This study provides critical insights into defect dynamics and opens up avenues for advanced applications of optoelectronic devices.