Spectral analysis on the carrier dynamics for efficient photon upconversion via molecules sensitized by ZnSe quantum dots.

Owing to the great potential in photochemical and photophysical applications, extensive efforts have been devoted to developing quantum dot-molecule (QD-M) hybrid systems. Particularly in the senario of photon upconversion, triplet energy transfer (TET) from the QD to molecule is a crutial process directly determining the performance. However, surface defects generally emerging in bare QDs will trap carriers and compete with TET process, which is harmful for efficient photon upconversion. Surface passivation by capping shell on QD can reduce carrier trapping. Nevertheless, it simultaneously suppresses TET. Herein, the ZnSe/ZnS-PTA (9-phenanthrene carboxylic acid) QD-M systems with different ZnS shell thickness are synthesized for synergistically passivating surface defects and optimizing TET towards high photon upconversion quantum yield (UCQY). Through combined spectral analysis, the results show unambiguous carrier dynamics of TET and carrier trapping, providing solid evidence for how TET competes with carrier trapping and achieving the highest UCQY. This systematic study could provide further insight for exploring the carrier dynamics in QD-M hybrid systems and benefit new applications in photon-converting nanomaterials.