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2. Laser-induced color centers in crystals

Author

Gao, Si, primary, Duan, Yan-Zhao, additional, Tian, Zhen-Nan, additional, Zhang, Yong-Lai, additional, Chen, Qi-Dai, additional, Gao, Bing-Rong, additional, and Sun, Hong-Bo, additional

Published
2022
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13. Direct Observation of Room‐Temperature Intravalley Coherent Coupling Processes in Monolayer MoS2.

Author

Yue, Yuan‐Yuan, Wang, Hai‐Yu, Wang, Lei, Zhao, Le‐Yi, Wang, Hai, Gao, Bing‐Rong, and Sun, Hong‐Bo

Subjects
FREQUENCIES of oscillating systems, EXCITED states, MONOMOLECULAR films, TRANSITION metals, EXCITON theory
Abstract

Comprehensive understanding of the interactions between excited states with spin‐valley polarizations is crucial for the applications of monolayer 2D transition metal dichalcogenides (TMDs) in spin‐valleytronics. Here, by broadband femtosecond transient absorption spectroscopy with circularly polarized pump/probe lights, a systematic investigation on the many‐body interactions of band‐edge valley excitons in monolayer MoS2 is performed, where intravalley coherent coupling processes are directly observed at room temperature. Namely, when the intravalley mixing states in the superposition region of A‐exciton and B‐exciton states are excited, there is an intravalley coherent coupling between A‐exciton and B‐exciton in K valley (or A′‐exciton and B′‐exciton in K′ valley) with an oscillation frequency of ≈7–8 THz, rather than the intervalley excitonic coupling in general. The findings elucidate intravalley mixing and coherent oscillations in valley excitons of monolayer TMDs at room temperature, which can give insight into the many‐body coupling mechanisms of excited valley excitons in 2D TMDs. [ABSTRACT FROM AUTHOR]

Published
2022
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17. Trion dynamics and charge photogeneration in MoS2 nanosheets prepared by liquid phase exfoliation.

Author

Yue, Yuan-Yuan, Zhao, Le-Yi, Han, Dan-Ao, Wang, Lei, Wang, Hai-Yu, Gao, Bing-Rong, and Sun, Hong-Bo

Abstract

Since excitonic quasiparticles, including excitons, trions and charges, have a great influence on the photoelectric characteristics of two-dimensional (2D) transition metal dichalcogenides (TMDs), systematic explorations of the trion dynamics and charge photogeneration in 2D TMDs are important for their future optoelectronic applications. Here, broadband femtosecond transient absorption spectroscopic experiments are performed first to investigate the peak shifting and broadening kinetics in MoS2 nanosheets in solution prepared by liquid phase exfoliation (LPE-MoS2, ∼9 layers, 9L), which reveal that the binding energies for the A-, B-, and C-exciton states are ∼77 meV, ∼76 meV, and −70 meV (the energy difference between free charges and excitons; the negative sign for C-excitons means a spontaneous dissociation nature in band-nesting regions), respectively. Then, the trion dynamics and charge photogeneration in LPE-MoS2 nanosheets have been studied in detail, demonstrating that they are comparable to those in chemical vapor deposition grown MoS2 films (1L-, 3L- and 7L-MoS2). These experimental results suggest that LPE-TMD nanosheets also have the potential for use in charge-related optoelectronic devices based on 2D TMDs. [ABSTRACT FROM AUTHOR]

Published
2021
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19. Many-particle induced band renormalization processes in few- and mono-layer MoS2.

Author

Yue, Yuan-Yuan, Wang, Zhuo, Wang, Lei, Wang, Hai-Yu, Chen, Yang, Wang, Dan, Chen, Qi-Dai, Gao, Bing-Rong, Wee, Andrew T S, Qiu, Cheng-Wei, and Sun, Hong-Bo

Subjects
K-spaces, MONOMOLECULAR films
Abstract

Band renormalization effects play a significant role for two-dimensional (2D) materials in designing a device structure and customizing their optoelectronic performance. However, the intrinsic physical mechanism about the influence of these effects cannot be revealed by general steady-state studies. Here, band renormalization effects in organic superacid treated monolayer MoS2, untreated monolayer MoS2 and few-layer MoS2 are quantitatively analyzed by using broadband femtosecond transient absorption spectroscopy. In comparison with the untreated monolayer, organic superacid treated monolayer MoS2 maintains a direct bandgap structure with two thirds of carriers populated at K valley, even when the initial exciton density is as high as 2.05 × 1014 cm−2 (under 400 nm excitations). While for untreated monolayer and few-layer MoS2, many-particle induced band renormalizations lead to a stronger imbalance for the carrier population between K and Q valleys in k space, and the former experiences a direct-to-indirect bandgap transition when the initial exciton density exceeds 5.0 × 1013 cm−2 (under 400 nm excitations). Those many-particle induced band renormalization processes further suggest a band-structure-controlling method in practical 2D devices. [ABSTRACT FROM AUTHOR]

Published
2021
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28. Size-dependent one-photon- and two-photon-pumped amplified spontaneous emission from organometal halide CH3NH3PbBr3 perovskite cubic microcrystals.

Author

Zhang, Zhen-Yu, Wang, Hai-Yu, Zhang, Yan-Xia, Li, Kai-Jiao, Zhan, Xue-Peng, Gao, Bing-Rong, Chen, Qi-Dai, and Sun, Hong-Bo

Abstract

In the past few years, organometal halide light-emitting perovskite thin films and colloidal nanocrystals (NCs) have attracted significant research interest in the field of highly purified illuminating applications. However, knowledge of photoluminescence (PL) characteristics, such as amplified spontaneous emission (ASE) of larger-sized perovskite crystals, is still relatively scarce. Here, we presented room-temperature size-dependent spontaneous emission (SE) and ASE of the organometal halide CH3NH3PbBr3 perovskite cubic microcrystals pumped through one-photon-(1P) and two-photon-(2P) excitation paradigms. The results showed that the optical properties of SE and ASE were sensitively dependent on the sizes of perovskite microcrystals irrespective of whether 1P or 2P excitation was used. Moreover, by comparing the spectral results of 1P- and 2P-pumped experiments, 2P pumping was found to be an effective paradigm to reduce thresholds by one order of magnitude. Finally, we carried out fluences-dependent time-resolved fluorescence dynamics experiments to study the underlying effects of these scale-dependent SE and ASE. We found that the photoluminescence (PL) recombination rates sensitively became faster with increasing carriers’ densities, and that the ASE pumped from larger-sized CH3NH3PbBr3 perovskite cubic microcrystals showed faster lifetimes. This work shows that micro-sized perovskite cubic crystals could be the ideal patterns of perovskite materials for realizing ASE applications in the future. [ABSTRACT FROM AUTHOR]

Published
2017
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31. Research on the fabrication and property of hydrophobic antireflective infrared window

Author

Zhang Ran, Haraguchi Masanobu, Xu Weiwei, Cao Xiao-Wen, and Gao Bing-Rong

Subjects
Materials science, Fabrication, Anti-reflective coating, Property (philosophy), law, business.industry, Infrared window, General Physics and Astronomy, Optoelectronics, business, law.invention
Abstract

We proposed a facile approach for rapid and maskless production of zinc sulfide microstructure used as antireflective and hydrophobic surface by direct laser interference ablation. This surface could improve the infrared transmittance from 75% to 92%; and the problem of bad film adhesion, corrosion resistance, and the thermal expansion mismatch in the antireflective coating membrane were solved. By this method a quick and simple fabrication, and a large-area production as well as the hydrophobic properties with a contact angle of 145° can be realized. Hence this approach can have future broad applications in areas of optoelectronics, solar energy, aerospace, and infrared guidance etc.

Published
2014

35. Elucidating the band structure and free charge carrier dynamics of pure and impurities doped CH3NH3PbI3−xClx perovskite thin films.

Author

Zhang, Zhen-Yu, Chen, Xin, Wang, Hai-Yu, Xu, Ming, Gao, Bing-Rong, Chen, Qi-Dai, and Sun, Hong-Bo

Abstract

CH3NH3PbI3−xClx perovskite material has been commonly used as the free charge generator and reservoir in highly efficient perovskite-based solid-state solar photovoltaic devices. However, many of the underlying fundamental photophysical mechanisms in this material such as the perovskite transition band structure as well as the dependent relationship between the carrier properties and lattice properties still lack sufficient understanding. Here, we elucidated the fundamental band structure of the pure CH3NH3PbI3−xClx pervoskite lattice, and then reported about the dependent relationship between the free charge carrier characteristic and the different CH3NH3PbI3−xClx pervoskite lattice thin films utilizing femtosecond time-resolved pump–probe technologies. The data demonstrated that the pure perovskite crystal band structure should only have one conduction and one valence band rather than dual valences, and the pure perovskite lattice could trigger more free charge carriers with a slower recombination rate under an identical pump intensity compared with the impurities doped perovskite crystal. We also investigated the perovskite film performance when exposed to moisture and water, the corresponding results gave us a dip in the optimization of the performance of perovskite based devices, and so as a priority this material should be isolated from moisture (water). This work may propose a deeper perspective on the comprehension for this material and it is useful for future optimization of applications in photovoltaic and light emission devices. [ABSTRACT FROM AUTHOR]

Published
2015
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49. PerovskiteCavity Complex: the Modulated Optical Characteristics of Organometallic Halide Perovskite CH3NH3PbIxCl3–xDoped in Length Tunable Optical Microcavities

Author

Zhang, Zhen-Yu, Wang, Hai-Yu, Li, Kai-Jiao, Xu, Ming, Wang, Hai, Gao, Bing-Rong, Chen, Qi-Dai, and Sun, Hong-Bo

Abstract

When organometallic halide perovskite semiconductors with continuous transition band were placed into an optical microcavity, interaction/modulation effect between confined photonic mode supported by cavity and free charge carriers mode triggered in perovskite occurred. In this metal–insulator–metal (MIM) microcavity, given the broad absorption region of perovskite CH3NH3PbIxCl3–x, the cavity resonant energy can be selectively designed to modulate the photophysical characteristics of perovskite charge carriers at different levels. Another advantage of using perovskite is that its band filling effect (charge carrier’s accumulation process) and relaxation process could last for few and hundreds picoseconds respectively, allowing us to accurately examine the time-resolved couple modulating effect by microcavities. Steady-state and transient absorption (TA) spectra were carried out to experimentally confirm the modulation effect of microcavity on optical characteristics of perovskite free charge carriers. It is found that created binate new states around cavity-perovskite resonance emerged at different perovskite levels are mutually independent. Interestingly, the band filling process of these new states is found not affected while their fluence-dependent relaxation process is accelerated by microcavities. The results in our work show that we can selectively manipulate the optical characteristics (absorption and charge carriers lifetimes) of perovskite by length tunable optical microcavities. Our efforts may propose an interesting modulating system and trigger potential optical application based on perovskite–light complex.

Published
2016
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