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704 results on '"Wong, Kam Sing"'

151. Kilohertz femtosecond UV-pumped visible beta-barium borate and lithium triborate optical parametric generator and amplifier

Author

Wang, Hong, Wong, Kam Sing, Deng, Daoqun, Xu, Zuyan, Wong, George K.L., and Zhang, Jingyuan

Subjects
Light amplifiers -- Analysis, Crystal optics -- Analysis, Astronomy, Physics
Abstract

We demonstrate optical parametric generation and amplification of femtosecond pulses in the entire visible range using type-I phase-matched [Beta]-barium borate and lithium triborate crystals pumped by the frequency-doubled output of a Ti:sapphire regenerative amplifier at 395 nm. The output is tunable from 470 to 770 nm with a pulse width of [approximately]170 fs at a repetition rate of i kHz and a maximum output energy of [approximately]1.1 [[micro]joule]/pulse. The visible optical parametric amplifier output was then frequency doubled and sum frequency mixed with the fundamental output of Ti:sapphire at 790 nm to produce UV pulses with a conversion efficiency of greater than 25%. The second harmonic generated UV pulses are tunable from 240 to 380 nm with a maximum pulse energy of [approximately]260 nJ/pulse. Key words: Femtosecond pulses, parametric generation and amplification.

Published
1997

154. Functionalized Acrylonitriles with Aggregation-Induced Emission: Structure Tuning by Simple Reaction-Condition Variation, Efficient Red Emission, and Two-Photon Bioimaging

Author

Niu, Guangle, primary, Zheng, Xiuli, additional, Zhao, Zheng, additional, Zhang, Haoke, additional, Wang, Jianguo, additional, He, Xuewen, additional, Chen, Yuncong, additional, Shi, Xiujuan, additional, Ma, Chao, additional, Kwok, Ryan T. K., additional, Lam, Jacky W. Y., additional, Sung, Herman H. Y., additional, Williams, Ian D., additional, Wong, Kam Sing, additional, Wang, Pengfei, additional, and Tang, Ben Zhong, additional

Published
2019
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155. Perovskite Bifunctional Device with Improved Electroluminescent and Photovoltaic Performance through Interfacial Energy‐Band Engineering

Author

Xie, Jiangsheng, primary, Hang, Pengjie, additional, Wang, Han, additional, Zhao, Shenghe, additional, Li, Ge, additional, Fang, Yanjun, additional, Liu, Feng, additional, Guo, Xinlu, additional, Zhu, Hepeng, additional, Lu, Xinhui, additional, Yu, Xuegong, additional, Chan, Christopher C. S., additional, Wong, Kam Sing, additional, Yang, Deren, additional, Xu, Jianbin, additional, and Yan, Keyou, additional

Published
2019
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156. Spontaneous Formation of Nanocrystals in Amorphous Matrix: Alternative Pathway to Bright Emission in Quasi‐2D Perovskites

Author

Liu, Fangzhou, primary, Chan, Christopher Chang Sing, additional, Ma, Chao, additional, Tam, Ho Won, additional, Leung, Tik Lun, additional, Lin, Jingyang, additional, Djurišić, Aleksandra B., additional, Wong, Kam Sing, additional, Popović, Jasminka, additional, Ng, Alan Man Ching, additional, Chan, Wai Kin, additional, Chen, Wei, additional, He, Zhubing, additional, Adesina, Ayotunde Emmanuel, additional, Foo, Yishu, additional, and Zapien, Juan Antonio, additional

Published
2019
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162. Drawing a clear mechanistic picture for the aggregation-induced emission process

Author

Zhang, Haoke, primary, Liu, Junkai, additional, Du, Lili, additional, Ma, Chao, additional, Leung, Nelson L. C., additional, Niu, Yingli, additional, Qin, Anjun, additional, Sun, Jingzhi, additional, Peng, Qian, additional, Sung, Herman H. Y., additional, Williams, Ian D., additional, Kwok, Ryan T. K., additional, Lam, Jacky W. Y., additional, Wong, Kam Sing, additional, Phillips, David Lee, additional, and Tang, Ben Zhong, additional

Published
2019
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163. Bulk Heterojunction Quasi-Two-Dimensional Perovskite Solar Cell with 1.18 V High Photovoltage

Author

Wang, Han, primary, Cheng, Guanghui, additional, Xie, Jiangsheng, additional, Zhao, Shenghe, additional, Qin, Minchao, additional, Chan, Christopher C. S., additional, Qiu, Yongcai, additional, Chen, Guangxu, additional, Duan, Chunhui, additional, Wong, Kam Sing, additional, Wang, Jiannong, additional, Lu, Xinhui, additional, Xu, Jianbin, additional, and Yan, Keyou, additional

Published
2018
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164. An Ultrathin Ferroelectric Perovskite Oxide Layer for High-Performance Hole Transport Material Free Carbon Based Halide Perovskite Solar Cells

Author

Yang, Yinglong, primary, Liu, Zhenghao, additional, Ng, Wai Kit, additional, Zhang, Lihua, additional, Zhang, Hua, additional, Meng, Xiangyue, additional, Bai, Yang, additional, Xiao, Shuang, additional, Zhang, Teng, additional, Hu, Chen, additional, Wong, Kam Sing, additional, and Yang, Shihe, additional

Published
2018
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165. Insight into the strong aggregation-induced emission of low-conjugated racemic C6-unsubstituted tetrahydropyrimidines through crystal-structure–property relationship of polymorphs† †Electronic supplementary information (ESI) available: General method, instruments, preparation of polymorphs, characterization data, 1H and 13C NMR of THP 3, Table S1 and S2, Fig. S1–S4, 'cif' files containing single-crystal X-ray diffraction data of 2c, 2c', 3p, 3b and 3c. CCDC 850811, 1011037–1011040. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc01226k Click here for additional data file. Click here for additional data file

Author

Zhu, Qiuhua, Zhang, Yilin, Nie, Han, Zhao, Zujin, Liu, Shuwen, Wong, Kam Sing, and Tang, Ben Zhong

Subjects
Chemistry
Abstract

Racemic low-conjugated non-emissive THPs 1–3 can form highly emissive RS- and RR/SS-packing polymorphs with mixed through-bond and through-space conjugation., Racemic C6-unsubstituted tetrahydropyrimidines (THPs) are a series of fluorophores with a strong aggregation-induced emission (AIE) effect. However, they do not possess the structural features of conventional AIE compounds. In order to understand their AIE mechanism, here, the influences of the molecular packing mode and the conformation on the optical properties of THPs were investigated using seven crystalline polymorphs of three THPs (1–3). The racemic THPs 1–3 have low-conjugated and highly flexible molecular structures, and hence show practically no emission in different organic solvents. However, the fluorescence quantum yields of their polymorphs are up to 93%, and the maximum excitation (λ ex) and emission (λ em) wavelengths of the polymorphs are long at 409 and 484 nm, respectively. Single-crystal structures and theoretical calculation of the HOMOs and LUMOs based on the molecular conformations of these polymorphs indicate that the polymorphs with the shortest λ ex and λ em values possess a RS-packing mode (R- and S-enantiomers self-assemble as paired anti-parallel lines) and a more twisted conformation without through-space conjugation between the dicarboxylates, but the polymorphs with longer λ ex and λ em values adopt a RR/SS-packing mode (R- and S-enantiomers self-assemble as unpaired zigzag lines) and a less twisted conformation with through-space conjugation between the dicarboxylates. The molecular conformations of 1–3 in all these polymorphs are stereo and more twisted than those in solution. Although 1–3 are poorly conjugated, the radiative rate constants (k r) of their polymorphs are as large as conventional fluorophores (0.41–1.03 × 108 s–1) because of improved electronic conjugation by both through-bond and through-space interactions. Based on the obtained results, it can be deduced that the strong AIE arises not only from the restriction of intramolecular motion but also from enhanced electronic coupling and radiatively-favored inter-crossed local excitation (LE) and intramolecular charge transfer (ICT) excitation states. The abnormal molecular structures, easily-controllable self-assembly of the R- and S-enantiomers, and the strong AIE effect make THPs very useful fluorophores for applications and theoretical research.

Published
2015

169. Mixed Spacer Cation Stabilization of Blue‐Emitting n = 2 Ruddlesden–Popper Organic–Inorganic Halide Perovskite Films.

Author

Leung, Tik Lun, Tam, Ho Won, Liu, Fangzhou, Lin, Jingyang, Ng, Alan Man Ching, Chan, Wai Kin, Chen, Wei, He, Zhubing, Lončarić, Ivor, Grisanti, Luca, Ma, Chao, Wong, Kam Sing, Lau, Ying Suet, Zhu, Furong, Skoko, Željko, Popović, Jasminka, and Djurišić, Aleksandra B.

Subjects
PEROVSKITE, CATIONS, HALIDES, HIGH temperature physics
Abstract

Ruddlesden–Popper halide perovskite (RPP) materials are of significant interest for light‐emitting devices since their emission wavelength can be controlled by tuning the number of layers n, resulting in improved spectral stability compared to mixed halide devices. However, RPP films typically contain phases with different n, and the low n phases tend to be unstable upon exposure to humidity, irradiation, and/or elevated temperature which hinders the achievement of pure blue emission from n = 2 films. In this work, two spacer cations are used to form an RPP film with mixed cation bilayer and high n = 2 phase purity, improved stability, and brighter light emission compared to a single spacer cation RPP. The stabilization of n = 2 phase is attributed to favorable formation energy, reduced strain, and reduced electron–phonon coupling compared to the RPP films with only one type of spacer cation. Using this approach, pure blue light‐emitting diodes (LEDs) with Commission Internationale de l'éclairage (CIE) coordinates of (0.156, 0.088) and excellent spectral stability are achieved. [ABSTRACT FROM AUTHOR]

Published
2020
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172. Bright Near-Infrared Aggregation-Induced Emission Luminogens with Strong Two-Photon Absorption, Excellent Organelle Specificity, and Efficient Photodynamic Therapy Potential

Author

Zheng, Zheng, primary, Zhang, Tianfu, additional, Liu, Haixiang, additional, Chen, Yuncong, additional, Kwok, Ryan T. K., additional, Ma, Chao, additional, Zhang, Pengfei, additional, Sung, Herman H. Y., additional, Williams, Ian D., additional, Lam, Jacky W. Y., additional, Wong, Kam Sing, additional, and Tang, Ben Zhong, additional

Published
2018
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174. Specific Two-Photon Imaging of Live Cellular and Deep-Tissue Lipid Droplets by Lipophilic AIEgens at Ultralow Concentration

Author

Niu, Guangle, primary, Zhang, Ruoyao, additional, Kwong, John P. C., additional, Lam, Jacky W. Y., additional, Chen, Congping, additional, Wang, Jianguo, additional, Chen, Yuncong, additional, Feng, Xing, additional, Kwok, Ryan T. K., additional, Sung, Herman H.-Y., additional, Williams, Ian D., additional, Elsegood, Mark R. J., additional, Qu, Jianan, additional, Ma, Chao, additional, Wong, Kam Sing, additional, Yu, Xiaoqiang, additional, and Tang, Ben Zhong, additional

Published
2018
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175. All-room-temperature solution-processed new nanocomposites based hole transport layer from synthesis to film formation for high-performance organic solar cells towards ultimate energy-efficient fabrication

Author

Huang, Zhanfeng, primary, Cheng, Jiaqi, additional, Ren, Xingang, additional, Zhuang, Jiaqing, additional, Roy, Vellaisamy A.L., additional, Burkhartsmeyer, Jeffrey Mark, additional, Wong, Kam Sing, additional, and Choy, Wallace C.H., additional

Published
2018
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179. Alkyl Chain Regiochemistry of Benzotriazole‐Based Donor Polymers Influencing Morphology and Performances of Non‐Fullerene Organic Solar Cells

Author

Chen, Shangshang, primary, Zhang, Lin, additional, Ma, Chao, additional, Meng, Dong, additional, Zhang, Jianquan, additional, Zhang, Guangye, additional, Li, Zhengke, additional, Chow, Philip C. Y., additional, Ma, Wei, additional, Wang, Zhaohui, additional, Wong, Kam Sing, additional, Ade, Harald, additional, and Yan, He, additional

Published
2018
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183. Mechanochromism: Multifunctional AIEgens: Ready Synthesis, Tunable Emission, Mechanochromism, Mitochondrial, and Bacterial Imaging (Adv. Funct. Mater. 1/2018)

Author

Jiang, Meijuan, primary, Gu, Xinggui, additional, Kwok, Ryan T. K., additional, Li, Ying, additional, Sung, Herman H. Y., additional, Zheng, Xiaoyan, additional, Zhang, Yilin, additional, Lam, Jacky W. Y., additional, Williams, Ian D., additional, Huang, Xuhui, additional, Wong, Kam Sing, additional, and Tang, Ben Zhong, additional

Published
2018
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186. Two-photon fabrication of photonic crystals by single-beam laser holographic lithography.

Author

Zhong, Yongchun, Zhou, Jianying, and Wong, Kam Sing

Subjects
PHYSICS research, SEMICONDUCTOR industry, PHOTONS, CRYSTALLOGRAPHY, ION beam lithography, PHOTONICS, CRYSTAL lattices
Abstract

We demonstrate a novel approach for the easy fabrication of photonic crystals (PCs) with arbitrary optical lattice using two-photon holographic lithography (HL). The quadratic dependence of the two-photon absorption process dramatically increases the contrast of the pattern and the low absorption coefficient of the photoresist at 720 nm lead to a high aspect ratio and low fluctuation of the pattern. By applying such a technique, defect-free and highly uniform one-dimensional gratings, two-dimensional quasicrystals, and three-dimensional (3D) face center cube-type PCs of high aspect ratio and small filling factor are obtained. This two-photon based HL technique is particularly suitable for making 3D PCs and quasicrystals with complex and fine structural details. [ABSTRACT FROM AUTHOR]

Published
2010
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188. Multifunctional AIEgens: Ready Synthesis, Tunable Emission, Mechanochromism, Mitochondrial, and Bacterial Imaging

Author

Jiang, Meijuan, primary, Gu, Xinggui, additional, Kwok, Ryan T. K., additional, Li, Ying, additional, Sung, Herman H. Y., additional, Zheng, Xiaoyan, additional, Zhang, Yilin, additional, Lam, Jacky W. Y., additional, Williams, Ian D., additional, Huang, Xuhui, additional, Wong, Kam Sing, additional, and Tang, Ben Zhong, additional

Published
2017
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189. Why Do Simple Molecules with “Isolated” Phenyl Rings Emit Visible Light?

Author

Zhang, Haoke, primary, Zheng, Xiaoyan, additional, Xie, Ni, additional, He, Zikai, additional, Liu, Junkai, additional, Leung, Nelson L. C., additional, Niu, Yingli, additional, Huang, Xuhui, additional, Wong, Kam Sing, additional, Kwok, Ryan T. K., additional, Sung, Herman H. Y., additional, Williams, Ian D., additional, Qin, Anjun, additional, Lam, Jacky W. Y., additional, and Tang, Ben Zhong, additional

Published
2017
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190. Study of the energy transfer processes in polyfluorene doped with tetraphenyl porphyrin.

Author

Lyons, Benjamin P., Wong, Kam Sing, and Monkman, Andrew P.

Subjects
*ENERGY transfer, *PORPHYRINS
Abstract

The energy transfer processes between polyfluorene and tetraphenyl porphyrin have been investigated through steady state and time resolved measurements. Radiative transfer is found to be negligible and so the results are analyzed in terms of Förster resonance energy transfer. Rate equations are fitted to the experimental data to obtain values for the concentration dependent energy transfer rate. From this, we calculate a value of 38 Å for the energy transfer distance. This compares well with the value for the F&oumlrster radius we calculate from the spectral overlap, even though Förster theory is not strictly valid for this system. [ABSTRACT FROM AUTHOR]

Published
2003
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192. Circularly Polarized Luminescence and a Reflective-Photoluminescent Chiral Nematic Liquid Crystal Display Based on an Aggregation-Induced Emission Luminogen

Author

Zhao, Dongyu, He, Hexiang, Gu, Xinggui, Guo, Lin, Wong, Kam Sing, Lam, Jacky W. Y., and Tang, Ben Zhong

Abstract

Chiral nematic liquid crystals (N*LCs) are a kind of smart material that can be obtained directly from cholesteric LCs or from nematic LCs by adding a chiral dopant. As a 1D photonic crystal, [ 1 ] the helical and periodic structure of a N*LC leads to unique optical properties, including selective reflection, circular dichroism (CD), optical rotation, and so on. [ 2–5 ] The most important property of N*LCs is the selective reflection of circularly polarized (CP) light. When N*LCs are sandwiched between two substrates with planar anchoring surfaces, CP light with the same handedness as the helix will be selectively reflected whereas light with opposite handedness will be transmitted.

Published
2016

194. Perovskite Solar Cells: Large-Grain Formamidinium PbI3- x Br x for High-Performance Perovskite Solar Cells via Intermediate Halide Exchange (Adv. Energy Mater. 12/2017)

Author

Long, Mingzhu, primary, Zhang, Tiankai, additional, Xu, Wangying, additional, Zeng, Xiaoliang, additional, Xie, Fangyan, additional, Li, Qiang, additional, Chen, Zefeng, additional, Zhou, Fengrui, additional, Wong, Kam Sing, additional, Yan, Keyou, additional, and Xu, Jianbin, additional

Published
2017
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196. A pure and stable intermediate phase is key to growing aligned and vertically monolithic perovskite crystals for efficient PIN planar perovskite solar cells with high processibility and stability

Author

Bai, Yang, primary, Xiao, Shuang, additional, Hu, Chen, additional, Zhang, Teng, additional, Meng, Xiangyue, additional, Li, Qiang, additional, Yang, Yinglong, additional, Wong, Kam Sing, additional, Chen, Haining, additional, and Yang, Shihe, additional

Published
2017
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