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A Study of Eu Doping in Nanolayers of CsPbBr <sub/>3</sub> using Ab Initio Calculations to Understand <i>fa??f</i> Transitions in Eu <sup>3+</sup> -Doped Nanocrystals for Light-Emitting Diodes
摘要： Recent experiments on Eu doped nanocrystals of CsPbX3 (X = Cl, Br) show that Eu exists in 3+ oxidation state even though it substitutes Pb which is in 2+ state in these perovskites. Therefore, the question arises, what is it that leads to the formation of Eu3+ in nanocrystals of these materials? In order to understand this, we have studied the doping of Eu in a slab (~1.8 nm thick) of CsPbBr3 from ab initio calculations and explored various possibilities that could lead to the formation of Eu3+ and the occurrence of f-f transitions. These include: 1) the presence of a Cs vacancy, 2) the existence of H or OH due to moisture, 3) substitution of O at a surface halogen site, and 4) the possibility of excess halogen around Eu. It is found that the presence of surface oxygen is the most likely reason for the observation of Eu3+ in these nanolayers. Our results show the presence of partially occupied spin-up f states and 6.48 μB magnetic moment on Eu that could lead to the possibility of f-f transition in these doped systems. A similar result has also been obtained for Eu doped in CsPbCl3 nanolayers. The calculated change in energy when defects/impurities are present gives favourable indication of finding H, OH, and Br as interstitials and O as substitutional entities, but Cs vacancy is unlikely. Additionally, we find that the doping of Eu in nanolayers does not affect the atomic structure and the cost of doping is also very small making these perovskites very promising materials for light emitting diodes and other solid-state lighting applications.
关键词： Two-dimensional systems,Light emitting diodes,Solid state lighting,Density functional theory,Metal-halide perovskites,Nanolayers,Defects,f-f transitions
更新于2025-09-23 15:19:57
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Multi-layered Parallel Plate Waveguide with Electrically and Magnetically Biased Graphene Walls
摘要： This paper focuses on the fault detection problem of 2-D systems described by the Roesser model. To detect faults effectively in the presence of disturbances, a fault detection ?lter is designed to satisfy a ?nite-frequency H? index and a ?nite-frequency H∞ index simultaneously. The corresponding ?nite-frequency performance analysis conditions are obtained by the aid of the generalized Kalman–Yakubovich–Popov lemma. Then, convex ?lter design conditions are derived by constructing a hyperplane tangent combined with linear matrix inequality techniques. An algorithm is proposed to construct a desired fault detection ?lter. Finally, a numerical example is given to show the effectiveness of the proposed method.
关键词： Fault detection,two-dimensional systems,?nite frequency,Roesser model
更新于2025-09-19 17:13:59
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[IEEE 2019 22nd International Multitopic Conference (INMIC) - Islamabad, Pakistan (2019.11.29-2019.11.30)] 2019 22nd International Multitopic Conference (INMIC) - Neuro based Integral Terminal Sliding Mode Nonlinear MPPT Control Paradigms for Stand-Alone Photovoltaic System
摘要： This paper focuses on the fault detection problem of 2-D systems described by the Roesser model. To detect faults effectively in the presence of disturbances, a fault detection ?lter is designed to satisfy a ?nite-frequency H? index and a ?nite-frequency H∞ index simultaneously. The corresponding ?nite-frequency performance analysis conditions are obtained by the aid of the generalized Kalman–Yakubovich–Popov lemma. Then, convex ?lter design conditions are derived by constructing a hyperplane tangent combined with linear matrix inequality techniques. An algorithm is proposed to construct a desired fault detection ?lter. Finally, a numerical example is given to show the effectiveness of the proposed method.
关键词： Fault detection,two-dimensional systems,?nite frequency,Roesser model
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Experimental Realization of Two-Dimensional PT-Symmetric Graphene: Bulk Properties and Edge States
摘要： The condition of real eigenvalue spectra in quantum mechanics is usually met by requiring operators to be Hermitian. This perception was challenged in 1988 by Carl M. Bender and Stefan Boettcher, who showed that parity-time (PT) symmetric Hamiltonians can have real spectra as well [1]. In photonics this concept was adopted by designing gain and loss structures for electromagnetic waves [2]. While numerous hallmark features [2] could be verified, experiments remained limited to one-dimensional settings. In this work we overcome this limitation and demonstrate a two-dimensional PT-symmetric system of photonic waveguides. We use this structure to study the interplay between a PT-phase transition and the emergence of topological edge states.
关键词： photonic waveguides,PT-symmetry,two-dimensional systems,topological edge states
更新于2025-09-16 10:30:52