24 results on '"Fang, Gaoliang"'
Search Results
2. Low-Ripple Continuous Control Set Model Predictive Torque Control for Switched Reluctance Machines Based on Equivalent Linear SRM Model.
- Author
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Fang, Gaoliang, Ye, Jin, Xiao, Dianxun, Xia, Zekun, and Emadi, Ali
- Subjects
- *
TORQUE control , *SWITCHED reluctance motors , *PREDICTION models , *COST functions , *MACHINERY , *TORQUE , *LAGRANGE multiplier , *WAVELET transforms - Abstract
In this article, a low-ripple continuous control set (CCS) model predictive torque control (MPTC) method for switched reluctance machines (SRMs) is proposed. The inherent high nonlinearity of the SRMs makes it difficult to solve the optimization problem in the CCS MPTC algorithm analytically. To address this issue, an equivalent linear SRM model is adopted, and the cost function is also properly modified. Then, with the torque boundary values provided by executing the voltage vectors of an improved switching table, the optimization problem in the CCS MPTC method becomes simple and analytically solvable. The Lagrange multiplier method is employed to solve this optimization problem analytically and generate the optimum torque reference values for the active phases. Based on the estimated torque variation rates, the duty cycles for each phase are calculated. Extensive simulation and experimental tests are carried out in a four-phase 8/6 SRM setup. These testing results reveal that the proposed CCS MPTC method shows much lower torque ripples and current ripples in a wide speed range with a low computational burden than the existing finite control set MPTC methods. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
3. Computational-Efficient Model Predictive Torque Control for Switched Reluctance Machines With Linear-Model-Based Equivalent Transformations.
- Author
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Fang, Gaoliang, Ye, Jin, Xiao, Dianxun, Xia, Zekun, and Emadi, Ali
- Subjects
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TORQUE control , *SWITCHED reluctance motors , *PREDICTION models , *MACHINERY , *TORQUE , *ELECTRIC inductance - Abstract
In this article, a novel model predictive torque control (MPTC) method for switched reluctance machines (SRMs) is proposed based on the equivalent linear SRM model and the improved switching table. First, an improved switching table with only six switching states is developed based on the inductance characteristics. The adoption of this improved switching table not only reduces the computational burden by 25% but also improves the torque control performance and system efficiency at high-speed region. However, the look-up-table (LUT) based MPTC methods suffer from occupying numerous storage space. To ease this issue, the simple linear SRM model is utilized. The flux-linkage and torque equivalent transformations are introduced to address the difference between the linear and nonlinear SRM models. With these transformations, the MPTC realized on the linear SRM model is proposed. Compared to 1530 storage units consumption to store three two-dimensional (2-D) LUTs in the LUT-based MPTC methods, the proposed method only occupies 228 storage units. Experimental results on an 8/6 SRM setup verify that the proposed method effectively eliminates the commutation torque ripple with lower execution time, less storage space, and improves the torque control performance at a high-speed range compared with the conventional LUT-based method. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
4. Lumped Radial Force Characteristics Reconstruction for Switched Reluctance Machines Through Scaling Flux-Linkage Characteristics.
- Author
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Fang, Gaoliang, Ye, Jin, Xiao, Dianxun, Xia, Zekun, and Emadi, Ali
- Subjects
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MAGNETIC declination , *MAGNETIC materials , *NOISE , *MAGNETIC properties , *ACTINIC flux - Abstract
This article presents a simple and practical method to estimate the lumped radial force characteristics for the switched reluctance machines (SRMs). First, the relationship between the square root of the lumped radial force and the flux linkage is discussed and analyzed. With the geometry data of the studied SRM, the abovementioned relationship under nominal air-gap length and nominal material magnetic property conditions can be obtained through the finite-element analysis (FEA) software. As the radial flux density dominates the magnitude of the radial force and it concentrates on the overlapping area, the abovementioned relationship is analyzed to be roughly held when the air-gap length and/or material magnetic property vary. Based on this relationship obtained from the FEA and the actual measured flux-linkage characteristics, the lumped radial force can be easily reconstructed for the actual SRMs regardless of the possible air-gap length variation and material magnetic property deviation during the manufacturing process. Simulation results on the 8/6 SRM and 12/8 SRM verify that the proposed method provides good radial force estimation results when the air-gap length is reduced or increased up to 50%. Superior estimation results are also observed on the condition that the magnetic ${B}$ – ${H}$ curve is linearly varied by ±25%. The accurate and simple radial force estimation method proposed in this article provides a solid basis for the radial-force-shaping-based advanced control methods to suppress the acoustic noise. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
5. A Regional Phase-Locked Loop-Based Low-Speed Position-Sensorless Control Scheme for General-Purpose Switched Reluctance Motor Drives.
- Author
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Xiao, Dianxun, Ye, Jin, Fang, Gaoliang, Xia, Zekun, Wang, Xueqing, and Emadi, Ali
- Subjects
SWITCHED reluctance motors ,RELUCTANCE motors ,MOTOR drives (Electric motors) ,PHASE-locked loops ,ELECTRIC inductance ,MAGNETIC hysteresis - Abstract
In this article, a general-purpose low-speed position estimation scheme using pulse injection is proposed for sensorless switched reluctance motor (SRM) drives. For the conventional low-speed sensorless control methods, magnetic characteristics are often used for position estimation, but it requires offline measurement and reduces the generality of sensorless control algorithms. To solve the issue, a new position estimator based on a regional phase-locked loop (RPLL) is designed. The approach utilizes a self-commissioning process to capture the unsaturated inductance adaptively at the initial stage. The RPLL is then adopted to estimate the full-cycle rotor position from the idle-phase inductance during sensorless operation. The speed-reversible sensorless control capability is also realized by a simple heterodyne design. Furthermore, stability analyses and parameter design are given to prove the robust local stability and convergence. Finally, comparative experimental validation is conducted on a 5.5-kW 12/8 SRM setup to verify the proposed method's effectiveness under both no-load and load conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
6. Discrete-Time Super-Twisting Sliding Mode Current Controller With Fixed Switching Frequency for Switched Reluctance Motors.
- Author
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Scalcon, Filipe P., Fang, Gaoliang, Vieira, Rodrigo P., Grundling, Hilton A., and Emadi, Ali
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SWITCHED reluctance motors , *SLIDING mode control , *COMPUTATIONAL complexity , *PULSE width modulation , *RELUCTANCE motors , *HYSTERESIS - Abstract
This article from a discrete-time model and stability analysis is developed using a Lyapunov approach, taking into account the one sample implementation delay present in digital control applications. Experimental results are provided to demonstrate the effectiveness of the proposed approach, where a conventional hysteresis controller is used as a benchmark. Results show that the proposal is able to deliver adequate reference tracking while using significantly lower sampling frequencies. Moreover, when compared to the hysteresis controller, superior tracking is observed at low speeds, while maintaining a similar level of computational complexity. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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- View/download PDF
7. Time-Efficient Torque Shaping for Switched Reluctance Machines From Linear Space.
- Author
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Fang, Gaoliang, Ye, Jin, Xiao, Dianxun, Xia, Zekun, Wang, Xueqing, and Emadi, Ali
- Subjects
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VECTOR spaces , *TORQUE , *LINEAR operators , *RELUCTANCE motors , *MACHINERY - Abstract
In this article, a time-efficient torque shaping technique for the switched reluctance machines is proposed to reduce the torque ripples while optimizing the copper loss. To reduce the computational time for solving the time-consuming bi-objective optimization problem, an efficient and desirable linear space for the SRM is utilized through the torque mapping between the linear space and nonlinear space. The feasible regions and properties of this torque mapping for SRM are studied in detail first. Then, based on this torque mapping, the current reference is generated by solving a convex optimization problem in the linear space and later converted to the current reference in nonlinear space. Compared to the traditional method that only adopts nonlinear space, the proposed current reference generation method requires less than 10% of the time. Furthermore, the proposed method saves more than 70% time consumed by the traditional method for the bi-objective optimization problem but possesses the similar torque ripple reduction performance. The effectiveness of the proposed method has been verified by extensive simulation and experimental tests on a four-phase 5.1 kW 8/6 SRM setup. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
8. Improved Feature-Position-Based Sensorless Control Scheme for SRM Drives Based on Nonlinear State Observer at Medium and High Speeds.
- Author
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Xiao, Dianxun, Ye, Jin, Fang, Gaoliang, Xia, Zekun, Wang, Xueqing, and Emadi, Ali
- Subjects
SWITCHED reluctance motors ,RELUCTANCE motors ,ROBUST control ,NONLINEAR control theory ,SPEED - Abstract
The article proposes a nonlinear state observer (NSO) for robust position-sensorless control of switched reluctance motor (SRM) drives over medium- and high-speed range. A classical reference flux-linkage method is adopted to capture a feature position of the SRM, which avoids the use of 3-D magnetic characteristics and has better universality. However, the estimation accuracy of this method would be deteriorated due to flux-linkage errors. To ease the problem, the NSO is developed to enhance the robustness against flux-linkage distortions for more accurate position and speed estimation. This observer can first reconstruct complete position information from a low-resolution feature position. The adverse impact of flux-linkage errors on position estimation is then investigated through a novel small-signal approximation and suppressed by an augmented state estimator. Afterward, a parameter design scheme is given to ensure the observer's stability and improve the capability in distortion suppression. To baseline the performance, comparative experimental validation between the proposed NSO and a widely used linear prediction method is conducted on a 12/8 SRM setup. The results show that the proposed strategy can improve the overall position-sensorless control performance in both the steady and transient states. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
9. Universal Full-Speed Sensorless Control Scheme for Interior Permanent Magnet Synchronous Motors.
- Author
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Xiao, Dianxun, Nalakath, Shamsuddeen, Filho, Silvio Rotilli, Fang, Gaoliang, Dong, Alice, Sun, Yingguang, Wiseman, Jason, and Emadi, Ali
- Subjects
PERMANENT magnet motors ,SPEED - Abstract
This article presents a general-purpose full-speed sensorless control scheme for interior permanent magnet synchronous motors (IPMSMs). By applying a quadratic extended back electromotive force (QBEMF) model, the injection-based and model-based position estimations can be combined into a universal sensorless control strategy for the full-speed operation. At low speed, the QBEMF model acts as a self-demodulator that can extract position information from arbitrary high-frequency currents without using digital filters. Therefore, it is suitable for any type of injection signals and can eliminate the adverse effect of filters. When the injection is removed at high speed, the same QBEMF model can still be used for position estimation, thereby solving the conventional transition issue from low-speed to high-speed sensorless control. In consequence, a unified algorithm is designed to achieve arbitrary injection for low-speed sensorless control and seamless transition across full-speed region. The proposed scheme is hence simpler and more effective compared to conventional full-speed sensorless methods. Finally, the feasibility of the proposed estimation algorithm is verified for a 15-kW IPMSM drive. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
10. Reduced-Coupling Coestimation of SOC and SOH for Lithium-Ion Batteries Based on Convex Optimization.
- Author
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Xiao, Dianxun, Fang, Gaoliang, Liu, Sheng, Yuan, Shaoyi, Ahmed, Ryan, Habibi, Saeid, and Emadi, Ali
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ALGORITHMS , *LITHIUM cells , *ELECTRIC vehicle batteries , *SODIUM ions , *COST functions - Abstract
Model-based state-of-charge (SOC) and state-of-health (SOH) estimation for lithium-ion batteries has been widely applied in electrified vehicles, while the SOC and SOH estimators are highly coupled and nonlinear in conventional techniques. This leads to a bulky design of observer network and complicates the stability analyses. In this article, a new reduced-decoupling SOC and SOH coestimation algorithm based on convex optimization is proposed. This scheme estimates the battery SOC from the battery model and does not require the classic Coulomb-counting method. Therefore, it can decouple the capacity estimation from the SOC estimator and reduce the strong interaction existing in conventional coestimation methods. Besides, all state variables can be solved together by one estimator, which is straightforward and avoids the complicated observer network. Owing to the decoupling design, the stability of the proposed method becomes more intuitive and can be always guaranteed according to the convexity analysis without using other stabilizing approaches. In consequence, a weak-interaction and robust coestimation algorithm of SOC and SOH can be realized by the proposed technique. The experiments on a 5.4-Ah lithium polymer battery are implemented to validate the feasibility of the algorithm. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
11. Torque Ripple and Efficiency Online Optimization of Switched Reluctance Machine Based on Torque per Ampere Characteristics.
- Author
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Song, Shoujun, Fang, Gaoliang, Hei, Runshan, Jiang, Jianan, Ma, Ruiqing, and Liu, Weiguo
- Subjects
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PERMANENT magnets , *TORQUE control , *RELUCTANCE motors , *TORQUE , *GENETIC algorithms , *MAGNETIC hysteresis - Abstract
Relatively high torque ripple limits the further development of the switched reluctance machine, and the application of the ripple suppression method will reduce the efficiency of the system. To simultaneously improve the efficiency and torque ripple of the switched reluctance machine, a new commutation and online optimization strategy is proposed. According to the torque per ampere characteristics of the machine, two rotor position angles are defined, which are the boundaries for the high and low torque per ampere operation modes of the two adjacent phases, respectively, and for different operating modes, specific torque hysteresis control schemes are performed. Furthermore, an objective function is constructed with the efficiency and torque ripple coefficient, and during the operation of the machine, the defined boundary angles are online optimized by the genetic algorithm to maximize the value of the objective function. The effectiveness of the method is verified by detailed simulation and experiment under different operating conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
12. Phase Current Reconstruction and Control of Three-Phase Switched Reluctance Machine With Modular Power Converter Using Single DC-Link Current Sensor.
- Author
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Song, Shoujun, Xia, Zekun, Fang, Gaoliang, Ma, Ruiqing, and Liu, Weiguo
- Subjects
MAGNETIZATION ,DIRECT currents ,CONVERTERS (Electronics) ,ELECTRIC power conversion ,SWITCHED reluctance motors - Abstract
According to the modular power converter, a novel phase current reconstruction method using single dc-link current sensor is proposed for three-phase switched reluctance machine (SRM), and the control method is implemented with the reconstructed phase current as well. A highly integrated modular power converter is constructed by a three-phase full bridge and a dual switch module. The phase windings are in star-connection, and the bipolar phase currents are applied. Based on the special operating modes and single pulse width modulation signal injection, the dc-link current is decoupled and the phase current in both magnetization and demagnetization regions is reconstructed, which is very critical for the implementation of some advanced methods that require complete period phase current. The conventional control methods of the SRM, such as single-pulse voltage and hysteresis current control methods, are carried out under different operating conditions with both simulation and experiment to verify the effectiveness of the proposed method, and the reconstruction errors and performance influences are detailed analyzed as well. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
13. Mn-Doped CsPbCl3 perovskite nanocrystals: solvothermal synthesis, dual-color luminescence and improved stability.
- Author
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Chen, Daqin, Fang, Gaoliang, Chen, Xiao, Zhong, Jiasong, Mao, Qinan, Zhou, Su, Li, Junni, and Lei, Lei
- Abstract
All inorganic CsPbX
3 (X = Cl, Br, I) perovskite quantum dots have attracted extreme attention due to their excellent optical performance. Unfortunately, heavy usage of the toxic Pb element is still a serious problem that needs to be solved. In the present work, Mn-doped CsPbCl3 nanocrystals are successfully prepared via a facile solvothermal reaction for the first time. A high Cs-to-Pb feeding ratio is necessary to achieve pure cubic perovskite phase and the incorporation of Mn dopants into the CsPbCl3 host is highly related to the Mn-to-Pb feeding ratio. Importantly, it is demonstrated that Mn-doped CsPbCl3 NCs synthesized by the solvothermal method have better stability than those prepared by traditional hot injection. To finely adjust the bandgap of CsPbCl3 NCs, Cl-to-Br anion exchange is used to fabricate Mn-doped CsPb(Cl/Br)3 NCs with tunable multi-color luminescence. Finally, the as-prepared Mn-doped CsPb(Cl/Br)3 products are demonstrated to be applicable as color converters for constructing white light-emitting diodes and optical thermometric medium for accurate temperature sensing. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
14. Unsaturated-Inductance-Based Instantaneous Torque Online Estimation of Switched Reluctance Machine with Locally Linearized Energy Conversion Loop.
- Author
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Song, Shoujun, Fang, Gaoliang, Zhang, Zhihui, Ma, Ruiqing, and Liu, Weiguo
- Subjects
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ELECTRIC inductance , *TORQUE , *ELECTRIC motors , *ENERGY conversion , *COMPUTER algorithms , *MECHANICAL energy - Abstract
This paper proposes a novel dynamic torque estimation method, which can quickly and accurately obtain the instantaneous torque with an online calculation based on the local linearization of the energy conversion loop on the flux linkage-current plane of the switched reluctance machine. According to the real-time information of the points on the loop, six situations are illustrated and analyzed. For each situation, the output mechanical energy is obtained first by calculating the area of the corresponding segmented regions, and then, the instantaneous torque is obtained by the difference algorithm concerning the output mechanical energy and rotor position. For the entire process, the unsaturated phase inductance of the machine, which can be conveniently measured, is the only information required in advance. To verify the effectiveness of the proposed method, detailed simulations and experiments are performed under different operating conditions. [ABSTRACT FROM PUBLISHER]
- Published
- 2018
- Full Text
- View/download PDF
15. Reverse synthesis of CsPbxMn1−x(Cl/Br)3 perovskite quantum dots from CsMnCl3 precursors through cation exchange.
- Author
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Ji, Zhenguo, Chen, Daqin, Lei, Lei, Fang, Gaoliang, Zhou, Su, Chen, Xiao, and Zhong, Jiasong
- Abstract
Successful development of all-inorganic CsPbX
3 (X = Cl, Br, or I) perovskite quantum dots (PQDs) has been witnessed due to their unique optical and electrical properties. However, the heavy usage of Pb element in PQDs has limited the commercial application of these PQDs, and the preparation of low-Pb or Pb-free PQDs is imperative. In this study, we report room-temperature reverse synthesis of CsPbx Mn1−x Cl3 PDQs from CsMnCl3 precursor nanocrystals through cation exchange. Interestingly, two-step phase transformation processes from hexagonal CsMnCl3 to rhombohedral Cs4 Pbx Mn1−x Cl6 and finally to cubic CsPbx Mn1−x Cl3 are evidenced. With an increase in the reaction time, Mn2+ ions in the PQD lattice are gradually replaced by Pb2+ ions. Notably, Mn2+ d → d broadband luminescence is not detected for the Cs4 Pbx Mn1−x Cl6 product, but it is intense for the CsPbx Mn1−x Cl3 sample owing to efficient energy transfer from CsPbCl3 to Mn2+ . Moreover, it is found that the introduction of Br− into the reaction system will prohibit the complete phase transformation from rhombohedral Cs4 Pbx Mn1−x (Cl/Br)6 to cubic CsPbx Mn1−x (Cl/Br)3 . By controlling the ratio between the CsMnCl3 precursor and PbBr2 , tunable luminescence is easily achieved due to the combined emissions from both CsPb(Cl/Br)3 PQDs and Mn2+ -emitting centers. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
16. High light harvesting efficiency CuInS2 quantum dots/TiO2/MoS2 photocatalysts for enhanced visible light photocatalytic H2 production.
- Author
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Yuan, Yong-Jun, Fang, Gaoliang, Chen, Daqin, Huang, Yanwei, Yang, Ling-Xia, Cao, Da-Peng, Wang, Jingjing, Yu, Zhen-Tao, and Zou, Zhi-Gang
- Subjects
- *
COPPER compounds , *QUANTUM dots , *TITANIUM dioxide - Abstract
Expanding the photoresponse range of TiO2-based photocatalysts is of great interest for photocatalytic H2 production. Herein, noble-metal-free CuInS2 quantum dots were employed as a novel inorganic dye to expand the visible light absorption of TiO2/MoS2 for solar H2 generation. The as-prepared CuInS2/TiO2/MoS2 photocatalysts exhibit broad absorption from the ultraviolet to near-infrared region. Under visible light irradiation (λ > 420 nm), the CuInS2/TiO2/MoS2 photocatalyst with 0.6 mmol g−1 CuInS2 and 0.5 wt% MoS2 showed the highest H2 evolution rate with a value of 1034 μmol h−1 g−1. Moreover, a considerable H2 evolution rate of 141 μmol h−1 g−1 was obtained under the irradiation of the optimized CuInS2/TiO2/MoS2 photocatalyst with >500 nm light. The reaction mechanism of the CuInS2/TiO2/MoS2 photocatalyst for photocatalytic H2 evolution was investigated in detail by photoluminescence decay study, and the results showed that the photoexcited electrons of CuInS2 can be transferred efficiently through TiO2 to MoS2 and then react with the absorbed protons to generate H2. The reported sensitization strategy tremendously improves the visible light absorption capacity and the photocatalytic performance of TiO2-based photocatalysts. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
17. Tunable CsPbBr3/Cs4PbBr6 phase transformation and their optical spectroscopic properties.
- Author
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Chen, Xiao, Chen, Daqin, Li, Junni, Fang, Gaoliang, Sheng, Hongchao, and Zhong, Jiasong
- Subjects
CESIUM compounds ,PHASE transitions ,OPTICAL spectroscopy - Abstract
As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics. On this basis, a new frontier of zero-dimensional perovskite-related Cs
4 PbBr6 with bright green emission and high stability has attracted an enormous amount of attention, even though its photoluminescence still requires to clarification. Herein, the controllable phase transformation between three-dimensional CsPbBr3 and zero-dimensional Cs4 PbBr6 is easily achieved in a facile ligand-assisted supersaturated recrystallization synthesis procedure via tuning the amount of surfactants, and their unique optical properties are investigated and compared in detail. Both Cs4 PbBr6 and CsPbBr3 produce remarkably intense green luminescence with quantum yields up to 45% and 80%, respectively; however, significantly different emitting behaviors are observed. The fluorescence lifetime of Cs4 PbBr6 is much longer than that of CsPbBr3 , and photo-blinking is easily detected in the Cs4 PbBr6 product, proving that the zero-dimensional Cs4 PbBr6 is indeed a highly luminescent perovskite-related material. Additionally, for the first time, tunable emissions over the visible-light spectral region are demonstrated to be achievable via halogen composition modulations in the Cs4 PbX6 (X = Cl, Br, I) samples. Our study brings a simple method for the phase control of CsPbBr3 /Cs4 PbBr6 and demonstrates the intrinsic luminescence nature of the zero-dimensional perovskite-related Cs4 PbX6 products. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
18. Noble-metal-free MoS2 nanosheet modified-InVO4 heterostructures for enhanced visible-light-driven photocatalytic H2 production.
- Author
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Kong, Zhe, Yuan, Yong-Jun, Chen, Daqin, Fang, Gaoliang, Yang, Yan, Yang, Shuhui, and Cao, Dapeng
- Subjects
MOLYBDENUM disulfide ,PRECIOUS metals ,PHOTOCATALYSTS - Abstract
Noble-metal-free, visible-light-responsive and “green” MoS
2 nanosheet modified-InVO4 heterostructures were synthesized as efficient photocatalysts for photocatalytic H2 production. The positive effect of intimate nanojunctions formed between MoS2 and InVO4 resulted in the excellent activity of MoS2 /InVO4 which is even higher than that of Pt-loaded InVO4 . [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
19. Fast Room-Temperature Cation Exchange Synthesis of Mn-Doped CsPbCl 3 Nanocrystals Driven by Dynamic Halogen Exchange.
- Author
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Chen D, Zhou S, Fang G, Chen X, and Zhong J
- Abstract
Currently, it is of great challenge to achieve cation exchange in CsPbX
3 (X = Cl, Br, I) perovskite nanocrystals (NCs) on account of rigid Pb2+ octahedral coordination protected by six halogen anions (PbX6 4- ). Herein, we demonstrate that dynamic halogen exchange can effectively open up PbX6 4- octahedrons and enable fast Mn-to-Pb cation exchange at room temperature in a few seconds. Importantly, Cl concentration rather than Mn one is demonstrated to be a dominant factor for cation exchange, where different Mn2+ /Cl- salts can be adopted as Mn/Cl sources and Cl-to-Cl or Cl-to-Br anion exchange is the necessary prerequisite. Such a facile synthesizing method can lead to the feasibility of tuning emissive colors for the Mn-doped CsPb(Cl/Br)3 NCs by controlling both cation and anion exchanges and open a new way to replace Pb2+ in CsPbX3 NCs by other nontoxic metal elements.- Published
- 2018
- Full Text
- View/download PDF
20. High light harvesting efficiency CuInS 2 quantum dots/TiO 2 /MoS 2 photocatalysts for enhanced visible light photocatalytic H 2 production.
- Author
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Yuan YJ, Fang G, Chen D, Huang Y, Yang LX, Cao DP, Wang J, Yu ZT, and Zou ZG
- Abstract
Expanding the photoresponse range of TiO2-based photocatalysts is of great interest for photocatalytic H2 production. Herein, noble-metal-free CuInS2 quantum dots were employed as a novel inorganic dye to expand the visible light absorption of TiO2/MoS2 for solar H2 generation. The as-prepared CuInS2/TiO2/MoS2 photocatalysts exhibit broad absorption from the ultraviolet to near-infrared region. Under visible light irradiation (λ > 420 nm), the CuInS2/TiO2/MoS2 photocatalyst with 0.6 mmol g-1 CuInS2 and 0.5 wt% MoS2 showed the highest H2 evolution rate with a value of 1034 μmol h-1 g-1. Moreover, a considerable H2 evolution rate of 141 μmol h-1 g-1 was obtained under the irradiation of the optimized CuInS2/TiO2/MoS2 photocatalyst with >500 nm light. The reaction mechanism of the CuInS2/TiO2/MoS2 photocatalyst for photocatalytic H2 evolution was investigated in detail by photoluminescence decay study, and the results showed that the photoexcited electrons of CuInS2 can be transferred efficiently through TiO2 to MoS2 and then react with the absorbed protons to generate H2. The reported sensitization strategy tremendously improves the visible light absorption capacity and the photocatalytic performance of TiO2-based photocatalysts.
- Published
- 2018
- Full Text
- View/download PDF
21. Tunable CsPbBr 3 /Cs 4 PbBr 6 phase transformation and their optical spectroscopic properties.
- Author
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Chen X, Chen D, Li J, Fang G, Sheng H, and Zhong J
- Abstract
As a novel type of promising materials, metal halide perovskites are a rising star in the field of optoelectronics. On this basis, a new frontier of zero-dimensional perovskite-related Cs4PbBr6 with bright green emission and high stability has attracted an enormous amount of attention, even though its photoluminescence still requires to clarification. Herein, the controllable phase transformation between three-dimensional CsPbBr3 and zero-dimensional Cs4PbBr6 is easily achieved in a facile ligand-assisted supersaturated recrystallization synthesis procedure via tuning the amount of surfactants, and their unique optical properties are investigated and compared in detail. Both Cs4PbBr6 and CsPbBr3 produce remarkably intense green luminescence with quantum yields up to 45% and 80%, respectively; however, significantly different emitting behaviors are observed. The fluorescence lifetime of Cs4PbBr6 is much longer than that of CsPbBr3, and photo-blinking is easily detected in the Cs4PbBr6 product, proving that the zero-dimensional Cs4PbBr6 is indeed a highly luminescent perovskite-related material. Additionally, for the first time, tunable emissions over the visible-light spectral region are demonstrated to be achievable via halogen composition modulations in the Cs4PbX6 (X = Cl, Br, I) samples. Our study brings a simple method for the phase control of CsPbBr3/Cs4PbBr6 and demonstrates the intrinsic luminescence nature of the zero-dimensional perovskite-related Cs4PbX6 products.
- Published
- 2018
- Full Text
- View/download PDF
22. Silica-Coated Mn-Doped CsPb(Cl/Br) 3 Inorganic Perovskite Quantum Dots: Exciton-to-Mn Energy Transfer and Blue-Excitable Solid-State Lighting.
- Author
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Chen D, Fang G, and Chen X
- Abstract
Tunability of emitting colors of perovskite quantum dots (PQDs) was generally realized via composition/size modulation. Due to their bandgap absorption and ionic crystal features, the mixing of multiple PQDs inevitably suffers from reabsorption and anion-exchange effects. Herein, we address these issues with high-content Mn
2+ -doped CsPbCl3 PQDs that can yield blue-excitable orange Mn2+ emission benefited from exciton-to-Mn energy transfer and Cl-to-Br anion exchange. Silica-coating was applied to improve air stability of PQDs, suppress the loss of Mn2+ , and avoid anion-exchange between different PQDs. As a direct benefit of intense multicolor emissions from Mn2+ -doped PQD@SiO2 solid phosphors, a prototype white light-emitting diode with excellent optical performance and superior light stability was constructed using green CsPbBr3 @SiO2 and orange Mn: CsPb(Cl/Br)3 @SiO2 composites as color converters, verifying their potential applications in the field of optoelectronics.- Published
- 2017
- Full Text
- View/download PDF
23. Full-Spectral Fine-Tuning Visible Emissions from Cation Hybrid Cs 1-m FA m PbX 3 (X = Cl, Br, and I, 0 ≤ m ≤ 1) Quantum Dots.
- Author
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Chen D, Chen X, Wan Z, and Fang G
- Abstract
Full-color visible emissions are particularly crucial for applications in displays and lightings. In this work, we developed a facile room-temperature ligand-assisted supersaturated recrystallization synthesis of monodisperse, cubic structure Cs
1-m FAm PbX3 (X = Cl, Br, and I or their mixtures Cl/Br and Br/I, 0 ≤ m ≤ 1) hybrid perovskite quantum dots (QDs). Impressively, cation substitution of Cs+ by FA+ was beneficial in finely tuning the band gap and in exciton recombination kinetics, improving the structural stability, and raising the absolute quantum yields up to 85%. With further assistance of anion replacement, full-spectral visible emissions in the wavelength range of 450-750 nm; narrow full width at half-maxima, and a wide color gamut, encompassing 130% of National Television System Committee television color standard, were achieved. Finally, Cs1-m FAm PbX3 -polymer films retaining multicolor luminescence are prepared and a prototype white light-emitting diode device was constructed using green Cs0.1 FA0.9 PbBr3 and red Cs0.1 FA0.9 Br1.5 I1.5 QDs as color converters, certainly suggesting their potential applications in the optoelectronics field.- Published
- 2017
- Full Text
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24. Noble-metal-free MoS 2 nanosheet modified-InVO 4 heterostructures for enhanced visible-light-driven photocatalytic H 2 production.
- Author
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Kong Z, Yuan YJ, Chen D, Fang G, Yang Y, Yang S, and Cao D
- Abstract
Noble-metal-free, visible-light-responsive and "green" MoS
2 nanosheet modified-InVO4 heterostructures were synthesized as efficient photocatalysts for photocatalytic H2 production. The positive effect of intimate nanojunctions formed between MoS2 and InVO4 resulted in the excellent activity of MoS2 /InVO4 which is even higher than that of Pt-loaded InVO4 .- Published
- 2017
- Full Text
- View/download PDF
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