Lead halide perovskites are known for their great potential in high-performance light-harvesting devices. We investigated the exciton recombination properties of 2D perovskites. We resolved two bright (optically allowed) exciton doublets and a dark (optically forbidden) exciton. Particularly, under the inherently strong electron-hole exchange interaction, each bright exciton doublet is split into two orthogonally orienting dipoles with large energy splitting of 2 meV, which is the largest experimental values in two-dimensional semiconductors. Furthermore, we observed an efficient transfer of oscillator strengths from the bright excitons to a dark exciton, which originates from strong spin-mixing between bright and dark excitons induced by external magnetic fields, and the optical emission from the dark exciton is brightened. Our results reveal that the physics on exciton recombination in 2D perovskites is rich, while the optical emission properties can be manipulated by external fields
Biosensor based on micro-ring resonator platform has attracted much attention owing to its high sensitivity for identifying various toxins in the environment. Among various bio-toxins, Botulinum neurotoxin (BoNT) are one type of poisonous substances causing the life-threatening neuroparalytic disease and probably used as biological weapon. In our study, a silicon based micro-ring resonator is designed, fabricated and demonstrated to detect BoNT in water sources. First, the capture antibody is labelled on the surface of silicon waveguide for capturing BoNT. The amount of BoNT bound on the surface results in the change of the effective refractive index. As a result, the concentration of toxins can be sensed based on the resonant shift response. Before involving the detection antibody in the assay, the BoNT concentration can be detected in the range from 200 ng/mL to 1 μg/mL. For further improving LOD, a signal enhancement strategy is to use biotin conjugated detection antibody to form a sandwich structure, and then to bind streptavidin-HRP and biotin conjugated anti-HRP antibody. LOD can be improved to 30 ng/mL after linking the detection antibody. After associating with the layer-by-layer structure composed by HRP and anti-HRP antibody on the sandwich assay, LOD can be improved to several pg/mL. Based on this strategy, the process of signal enhancement is flexible to achieve target LOD. And it also can be regenerated and reused after a cycle of detection. Therefore, this platform shows a high potential to apply for robust, realtime and high sensitive detection for various bio-toxins in water sources.
CdS materials have shown promise in optical refrigeration. However, the current success of laser cooling is still limited to nanobelt morphology. It is, therefore, important to explore whether bulk crystal growth technology could provide high-quality materials for laser cooling studies. Herein, we have demonstrated CdS bulk crystal growth by a modified optical floating zone method. The low temperature and continuous displacement of the CdS crystalline zone have resulted in high-quality CdS bulk crystals, which show strong photoluminescence upconversion with the absence of the long-wavelength and broad emission centered ∼700 nm that commercial CdS wafers usually exhibit. All these characterizations have confirmed the excellent stoichiometric nature and crystal quality of CdS bulk crystals, which is much better than the commercial counterparts for laser cooling studies.
We have demonstrated the first net laser cooling of semiconductors using CdS nanoribbons (or
nanobelts) in this work. This net cooling effect is found to be facilitated by resonant high order annihilation of
longitudinal optical (LO) phonons due to a strong exciton-LO phonon Fröhlich interactions. Using a pumpprobe
luminescence thermometry technique to measure the local temperature change, we have achieved as large
as 40 K cooling temperature from room temperature pumped by a 514 nm laser while a 532 nm laser pumping
led to a cooling of 20 K. At 100 K, only the 532 nm laser pumping can lead to a net cooling of around 15 K. Our
work opens new directions to search laser cooling semiconductors and makes it feasible to achieve all solid-state
cryocoolers based on semiconductors.
Conference Committee Involvement (11)
Quantum Dots, Nanostructures, and Quantum Materials: Growth, Characterization, and Modeling XVII
5 February 2020 | San Francisco, California, United States
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XVI
6 February 2019 | San Francisco, California, United States
Photonic Heat Engines: Science and Applications
3 February 2019 | San Francisco, California, United States
Optical and Electronic Cooling of Solids III
30 January 2018 | San Francisco, California, United States
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XV
29 January 2018 | San Francisco, California, United States
Optical and Electronic Cooling of Solids II
1 February 2017 | San Francisco, California, United States
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XIV
30 January 2017 | San Francisco, California, United States
Optical and Electronic Cooling of Solids
17 February 2016 | San Francisco, California, United States
Quantum Dots and Nanostructures: Growth, Characterization, and Modeling XIII
15 February 2016 | San Francisco, California, United States
Laser Refrigeration of Solids VIII
11 February 2015 | San Francisco, California, United States
Laser Refrigeration of Solids VII
5 February 2014 | San Francisco, California, United States
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