Upconverting semiconductor quantum dots (QDs) combine the stability of an inorganic crystalline structure with the spectral tunability afforded by quantum confinement. Here, we present upconverting type-II/type-I colloidal double QDs that enable enhancement of the performance of near-infrared to visible photon upconversion in QDs and broadening the range of relevant materials used. The resulting ZnTe/CdSe@CdS@CdSe/ZnSe type-II/type-I double QDs possess a very high photoluminescence quantum yield, monoexponential decay dynamics, and a narrow line width, approaching those of state-of-the-art upconverting QDs. We quantitatively characterize the upconversion cross section by direct comparison with two-photon absorption when varying the pump frequency across the absorption edge. Finally, we show that these upconversion QDs maintain their optical performance in a much more demanding geometry of a dense solid film and can thus be incorporated in devices as upconversion films. Our design provides guidance for fabricating highly efficient upconverting QDs with potential applications such as security coding and bioimaging.

中文翻译：

---

基于II型/I型异质结构的明亮近红外到可见光上转换双量子点

上转换半导体量子点 (QD) 将无机晶体结构的稳定性与量子限制提供的光谱可调性相结合。在这里，我们提出了上转换 II 型/I 型胶体双量子点，它们能够增强 QD 中近红外到可见光子上转换的性能，并拓宽相关材料的使用范围。由此产生的 ZnTe/CdSe@CdS@CdSe/ZnSe II 型/I 型双 QD 具有非常高的光致发光量子产率、单指数衰减动力学和窄线宽，接近最先进的上转换 QD . 当改变吸收边缘的泵浦频率时，我们通过与双光子吸收的直接比较来定量表征上转换截面。最后，我们表明，这些上转换 QD 在更苛刻的致密固体薄膜几何结构中保持其光学性能，因此可以作为上转换薄膜并入设备中。我们的设计为制造具有安全编码和生物成像等潜在应用的高效上转换 QD 提供了指导。