DEPARTMENT OF APPLIED PHYSICS 134 Email siu.fung.yu@polyu.edu.hk Qualification BEng (University College London) PhD (University of Cambridge) ORCID ID 0000-0003-0354-3767 Prof. YU Siu-fung Professor Research Overview Lasers, Optoelectronics Semiconductor Devices, Computer Simulation of Optoelectronics, Laser Application in Stress Analysis. Representative Publication • S.F. Yu, Analysis and Design of Vertical Cavity Surface Emitting Lasers, Wiley Series in Lasers and Applications, Wiley-Interscience, 445 pg., 2003 Recent Representative Results Two-dimensional Ruddlesden – Popper perovskites (RPPs) with multiple quantum well-like structures, strong excitonic quantum confinement, and high stability are promising optical gain media. However, the lasing from such material with a small number of inorganic well layers is difficult to achieve. Herein, we demonstrate the low-threshold upconversion lasing from the homologous RPP (PEA)2(MA)n−1PbnI3n+1 (n = 2 and 3) microflakes with wavelength varies from 598 to 637 nm under 800 nm laser excitation at low temperature (≤153 K). Using the micro Z-scan technique, we discovered that the RPP flakes have a giant two-photon absorption coefficient β as high as 3.6 × 103 cm GW–1, resulting in the effective upconversion transition under two-photon excitation. Furthermore, the self-formation of Fabry-Pérot microcavities provides the support for lasing emission from the n ≥ 2 RPP flakes. Calculation results and microscopic transient absorption measurements reveal that low-threshold lasing is due to the high differential gain coefficient and the suppressed nonradiative Auger recombination rate inside the quantum confinement structures. These properties enable RPPs as potential gain media for developing upconversion microcavity lasers. Patents US and China patents: • 深紫外微腔雷射器, Wang, T. & Yu, S. F., 3 May 2022, Patent No. 201911024539X, 25 Oct 2019 • 深紫外微腔雷射器及其製備方法, Wang, T. & Yu, S. F., 12 Apr 2022, Patent No. 201910827798.X, 3 Sep 2019 • 一種原位透射電子顯微鏡觀測納米顆粒生長的方法, Yu, S. F., Wang, T. & XU Hui, 24 Sep 2021, Patent No. ZL 2017109530153, 13 Oct 2017
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