Lai Runchen, Wu Kaifeng
State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China.
J Chem Phys. 2020 Sep 21;153(11):114701. doi: 10.1063/5.0023052.
Charge and/or energy transfer from photoexcited quantum dots (QDs) is often suppressed by a wide-bandgap shell. Here, we report an interesting, counter-intuitive observation that interfacial triplet energy transfer from QDs is not retarded but rather enabled by an insulating shell. Specifically, photoluminescence of red-emitting CdSe QDs could not be quenched by surface-anchored Rhodamine B molecules; in contrast, after ZnS shell coating, their emission was effectively quenched. Time-resolved spectroscopy reveals that the shell eliminates ultrafast hole trapping in the QDs and hence opens up the triplet exciton transfer pathway. The triplet energy of Rhodamine B can be reversely transferred back to QDs by thermal activation, or it can be passed to triplet acceptors in the solution. Capitalizing on the latter, we demonstrate red-to-blue photon upconversion based on QD-sensitized triplet-triplet annihilation with an efficiency of 2.8% and an anti-Stokes shift of 1.13 eV.
光激发量子点（QD）的电荷和/或能量转移常常会被宽带隙壳层抑制。在此，我们报告了一个有趣且与直觉相悖的观察结果：量子点的界面三重态能量转移并非受到抑制，而是由绝缘壳层促成。具体而言，表面锚定的罗丹明B分子无法淬灭红色发光CdSe量子点的光致发光；相比之下，在包覆ZnS壳层后，它们的发射被有效淬灭。时间分辨光谱表明，壳层消除了量子点中超快的空穴俘获，从而开辟了三重态激子转移途径。罗丹明B的三重态能量可通过热激活反向转移回量子点，或者传递给溶液中的三重态受体。利用后者，我们展示了基于量子点敏化三重态-三重态湮灭的红到蓝光上转换，效率为2.8%，反斯托克斯位移为1.13 eV。
