Gray Victor, Xia Pan, Huang Zhiyuan, Moses Emily, Fast Alexander, Fishman Dmitry A, Vullev Valentine I, Abrahamsson Maria, Moth-Poulsen Kasper, Lee Tang Ming
Department of Chemistry and Chemical Engineering , Chalmers University of Technology , 412 96 Gothenburg , Sweden.
Materials Science & Engineering Program , University of California, Riverside , 900 University Ave. , Riverside , CA 92521 , USA.
Chem Sci. 2017 Aug 1;8(8):5488-5496. doi: 10.1039/c7sc01610g. Epub 2017 May 31.
Herein we report the first example of nanocrystal (NC) sensitized triplet-triplet annihilation based photon upconversion from the visible to ultraviolet (vis-to-UV). Many photocatalyzed reactions, such as water splitting, require UV photons in order to function efficiently. Upconversion is one possible means of extending the usable range of photons into the visible. Vis-to-UV upconversion is achieved with CdS/ZnS core-shell NCs as the sensitizer and 2,5-diphenyloxazole (PPO) as annihilator and emitter. The ZnS shell was crucial in order to achieve any appreciable upconversion. From time resolved photoluminescence and transient absorption measurements we conclude that the ZnS shell affects the NC and triplet energy transfer (TET) from NC to PPO in two distinct ways. Upon ZnS growth the surface traps are passivated thus increasing the TET. The shell, however, also acts as a tunneling barrier for TET, reducing the efficiency. This leads to an optimal shell thickness where the upconversion quantum yield (') is maximized. Here the maximum ' was determined to be 5.2 ± 0.5% for 4 monolayers of ZnS shell on CdS NCs.
在此，我们报道了首例基于纳米晶体（NC）敏化的三重态-三重态湮灭的从可见光到紫外光（可见光到紫外光）的光子上转换。许多光催化反应，如水分解，为了有效发挥作用需要紫外光子。上转换是将光子的可用范围扩展到可见光的一种可能手段。以CdS/ZnS核壳纳米晶体作为敏化剂，2,5-二苯基恶唑（PPO）作为湮灭剂和发射体实现了可见光到紫外光的上转换。为了实现任何可观的上转换，ZnS壳层至关重要。从时间分辨光致发光和瞬态吸收测量中我们得出结论，ZnS壳层以两种不同方式影响纳米晶体以及从纳米晶体到PPO的三重态能量转移（TET）。随着ZnS生长，表面陷阱被钝化，从而增加了TET。然而，壳层也作为TET的隧穿势垒，降低了效率。这导致了一个最佳壳层厚度，此时上转换量子产率（'）最大化。在此，对于CdS纳米晶体上4个单层的ZnS壳层，最大'值确定为5.2±0.5%。
