Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University (NTU), 21 Nanyang Link, SPMS-PAP 03-05, Singapore 637371, Singapore.
Energy Research Institute @ NTU (ERI@N), Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive, Singapore 637553, Singapore.
Nat Commun. 2017 May 12;8:15198. doi: 10.1038/ncomms15198.
Multiphoton absorption processes enable many technologically important applications, such as in vivo imaging, photodynamic therapy and optical limiting, and so on. Specifically, higher-order nonlinear absorption such as five-photon absorption offers significant advantages of greater spatial confinement, increased penetration depth, reduced autofluorescence, enhanced sensitivity and improved resolution over lower orders in bioimaging. Organic chromophores and conventional semiconductor nanocrystals are leaders in two-/three-photon absorption applications, but face considerable challenges from their small five-photon action cross-sections. Herein, we reveal that the family of halide perovskite colloidal nanocrystals transcend these constraints with highly efficient five-photon-excited upconversion fluorescence-unprecedented for semiconductor nanocrystals. Amazingly, their multidimensional type I (both conduction and valence band edges of core lie within bandgap of shell) core-shell (three-dimensional methylammonium lead bromide/two-dimensional octylammonium lead bromide) perovskite nanocrystals exhibit five-photon action cross-sections that are at least 9 orders larger than state-of-the-art specially designed organic molecules. Importantly, this family of halide perovskite nanocrystals may enable fresh approaches for next-generation multiphoton imaging applications.
多光子吸收过程使许多技术重要的应用成为可能，例如在体成像、光动力疗法和光限幅等。具体来说，五光子吸收等高阶非线性吸收在生物成像中具有比低阶吸收更大的空间限制、更高的穿透深度、更低的自发荧光、更高的灵敏度和更好的分辨率等显著优势。有机发色团和传统半导体纳米晶体在双光子/三光子吸收应用中处于领先地位，但由于它们的五光子作用截面较小，面临着相当大的挑战。在此，我们揭示了卤化物钙钛矿胶体纳米晶体家族克服了这些限制，具有高效的五光子激发上转换荧光，这是半导体纳米晶体前所未有的。令人惊讶的是，它们的多维 I 型（核心的导带和价带边缘都在壳层的带隙内）核壳（三维甲基铵铅溴/二维辛基铵铅溴）钙钛矿纳米晶体的五光子作用截面至少比最先进的专门设计的有机分子大 9 个数量级。重要的是，这种卤化物钙钛矿纳米晶体可能为下一代多光子成像应用提供新的方法。
