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.

中文翻译：

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基于三重态能量转移过程的红至蓝光子上转换不会受到延迟，但可以通过壳包被的量子点实现。

来自光激发量子点（QD）的电荷和/或能量转移通常被宽带隙壳抑制。在这里，我们报告了一个有趣的，违反直觉的观察，即量子点的界面三重态能量传递没有受到阻碍，而是由绝缘壳实现的。具体而言，发红光的CdSe量子点的光致发光不能通过表面锚定的若丹明B分子来猝灭。相反，ZnS壳涂层后，其发射被有效地淬灭。时间分辨光谱法表明，壳消除了量子点中的超快空穴陷阱，因此打开了三重态激子转移途径。罗丹明B的三重态能量可以通过热激活反向传递回QD，或者可以传递给溶液中的三重态受体。利用后者，