16 research outputs found
Bulk Assembly of Organic Metal Halide Nanoribbons
Organic metal halide hybrids with low-dimensional structures at the molecular
level have received great attention recently for their exceptional structural
tunability and unique photophysical properties. Here we report for the first
time the synthesis and characterization of a one-dimensional (1D) organic metal
halide hybrid material, which contains metal halide nanoribbons with a width of
three octahedral units. It is found that this material with a chemical formula
CHNPbCl shows a dual emission with a
photoluminescence quantum efficiency (PLQE) of around 25% under ultraviolet
(UV) light irradiation. Photophysical studies and density functional theory
(DFT) calculations suggest the coexisting of delocalized free excitons and
localized self-trapped excitons in metal halide nanoribbons leading to the dual
emission. This work shows once again the exceptional tunability of organic
metal halide hybrids that bridge between molecular systems with localized
states and crystalline ones with electronic bands.Comment: 6 pages, 4 figures, plus supporting informatio
Surface Effects on Anisotropic Photoluminescence in One-Dimensional Organic Metal Halide Hybrids
One-dimensional (1D) organic metal halide hybrids exhibit strongly
anisotropic optical properties, highly efficient light emission, and large
Stokes shift, holding promises for novel photodetection and lighting
applications. However, the fundamental mechanisms governing their unique
optical properties and in particular the impacts of surface effects are not
understood. Here, we investigate 1D C4N2H14PbBr4 by polarization-dependent
time-averaged and time-resolved photoluminescence (TRPL) spectroscopy, as a
function of photoexcitation energy. Surprisingly, we find that the emission
under photoexcitation polarized parallel to the 1D metal halide chains can be
either stronger or weaker than that under perpendicular polarization, depending
on the excitation energy. We attribute the excitation-energy-dependent
anisotropic emission to fast surface recombination, supported by
first-principles calculations of optical absorption in this material. The fast
surface recombination is directly confirmed by TRPL measurements, when the
excitation is polarized parallel to the chains. Our comprehensive studies
provide a more complete picture for a deeper understanding of the optical
anisotropy in 1D organic metal halide hybrids
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Understanding the Structure, Electronic, Phononic, Optical, and Mechanical Properties of Low-Dimensional Materials
Low-dimensional materials have attracted significant attention in the field of materials science and technology. These materials, characterized by their limited dimensions in one, two or three directions, exhibit exceptional properties different from those of their bulk counterparts. This deviation results from the interaction of quantum effects, surface interactions, and unique electronic structures, creating a wide range of innovative applications in various fields such as electronics, photonics, energy storage and more. This study not only reveals the scientific complexities of their behavior but also paves the way for disruptive innovations that could transform industries and transform our interactions with the world around us. In this work, I have studied different classes of low-dimensional materials such as bulk and monolayer transition-metal dichalcogenides, one-dimensional organic-metal halide hybrids, organic metal halide nanoribbons, BiTe and HfTe.In the opening chapter, I lay the groundwork by discussing fundamental theories crucial for our subsequent calculations. These theories encompass density functional theory, density functional perturbation theory, GW and Bethe-Salpeter equations and other fundamental concepts on Raman, and calculation methods for elastic tensors. Chapter 2 delves into a comprehensive analysis of the impact of introducing Ni into the bulk phases of MoS, with a particular focus on the mechanism supporting low wear for lubrication applications. This chapter also presents systematic doping studies conducted through first-principles calculations. Chapter 3 narrows the focus to examine the consequences of Ni doping on the monolayer phases of MoS, revealing the induction of various known and novel distorted phases. These induced phases bring forth unique properties, including those of ferroelectric materials, multiferroic semimetals, ferromagnetic polar metals, and the presence of multiple gaps in conduction bands. These findings have promising implications for applications in spintronics, intermediate band solar cells, and non-linear optics. In Chapter 4, the attention shifts to a low-energy nine-layer phase within transition-metal dichalcogenides, where we explore methods for characterizing this phase through Raman spectroscopy and powder diffraction. Additionally, we investigate its potential applications in piezoelectricity and valleytronics. Next Chapter 5 delves into understanding the anisotropic properties of one-dimensional organic-metal halide hybrids and the mechanism of broadband emission. This chapter introduces an innovative approach for determining exciton-phonon coupling and the self-trapped exciton structure using excited state forces within a GW/Bethe-Salpeter framework. Chapter 6 offers a concise overview of my contributions to other collaborative works on low-dimensional materials, encompassing organic-metal halide hybrids, organic metal halide nanoribbons, BiTe and HfTe. Finally, I conclude with reflections on the potential of low-dimensional materials, their current progress, and future prospects
Enhanced interlayer interactions in Ni-doped MoS2 , and structural and electronic signatures of doping site
Panoply of Ni-Doping-Induced Reconstructions, Electronic Phases, and Ferroelectricity in 1T-MoS<sub>2</sub>
The
distorted phases of monolayer 1T-MoS2 have distinct
electronic properties, with potential applications in optoelectronics,
catalysis, and batteries. We theoretically investigate the use of
Ni-doping to generate distorted 1T phases and find not only the ones
usually reported but also two further phases (3 × 3 and 4 ×
4), depending on the concentration and the substitutional or adatom
doping site. Corresponding pristine phases are stable after removal
of dopants, which might offer a potential route to experimental synthesis.
We find large ferroelectric polarizations, most notably in 3 ×
3 whichcompared to the recently measured 1T″has
100 times greater ferroelectric polarization, a lower energy, and
a larger band gap. Doped phases include exotic multiferroic semimetals,
ferromagnetic polar metals, and improper ferroelectrics with only
in-plane polarization switchable. The pristine phases have unusual
multiple gaps in the conduction bands with possible applications for
intermediate band solar cells, transparent conductors, and nonlinear
optics
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Enhanced interlayer interactions in Ni-doped MoS2, and structural and electronic signatures of doping site
Recommended from our members