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P K Giri - One of the best experts on this subject based on the ideXlab platform.

  • understanding the excitation wavelength dependent spectral shift and large Exciton Binding Energy of tungsten disulfide quantum dots and its interaction with single walled carbon nanotubes
    Journal of Colloid and Interface Science, 2020
    Co-Authors: Abhilasha Bora, Ruma Das, Larionette P L Mawlong, P K Giri
    Abstract:

    Abstract Herein, we investigate the origin of excitation wavelength dependent spectral features and high fluorescence quantum yield in fluorescent 2D tungsten disulfide (WS2) quantum dots (QDs) of average size 2.4 nm. The as-prepared WS2 QDs possess high optical bandgap and reasonably high fluorescence quantum yield ~15.4% in the green region without any functionalization. The broad photoluminescence (PL) spectrum consists of multiple peaks owing to emissions from Excitonic transitions and surface defect-related transitions. The excitation wavelength-dependent spectral redshift and narrowing of line shape in the PL peak are analyzed carefully, and it is attributed to the selective excitation/recombination of carriers from different Energy levels. The temperature-dependent PL analysis yields an Exciton Binding Energy of ~301 meV in the QDs. Furthermore, we study the interaction between fluorescent WS2 QDs and single-walled carbon nanotubes (SWCNTs) and explore the mechanism of systematic quenching of PL of QDs by SWCNTs. The nature of the Stern–Volmer plot is found to be linear, and the time-resolved fluorescence measurements reveal that the quenching follows primarily the static behavior. Our study further reveals that defect sites in SWCNTs primarily act as the Binding sites for WS2 QDs and form non-fluorescent complexes for effective quenching of the PL. The strong interaction between the WS2 QDs and the SWCNTs is evidenced from the spectral shift in the X-ray photoelectron spectroscopy and Raman peaks. Our study reveals the origin of excitation wavelength dependent PL emission from WS2 QDs and the nature of the interaction between WS2 QDs and SWCNTs, which are important for their applications in biomedical imaging and sensing, such as surface-enhanced Raman scattering, etc.

  • large Exciton Binding Energy high photoluminescence quantum yield and improved photostability of organo metal halide hybrid perovskite quantum dots grown on a mesoporous titanium dioxide template
    Journal of Colloid and Interface Science, 2019
    Co-Authors: Sumaiya Parveen, Kamal Kumar Paul, Ruma Das, P K Giri
    Abstract:

    Abstract Herein, we demonstrated a novel synthetic route to grow size-tunable hybrid perovskite (CH3NH3PbI3 and CH3NH3PbBr3) quantum dots (QDs) using a Fluorine-doped TiO2 (F-TiO2) mesoporous template and these QDs exhibit large Exciton Binding Energy, high photoluminescence quantum yield and improved photostability. The pore size in F-TiO2 template is tuned by varying the HF molar concentration during its solvothermal growth and size of the perovskite QDs embedded in F-TiO2 pores is tuned in the range 1.7–5.1 nm, as revealed from the TEM analysis. A systematic blue-shift in UV–visible absorption edge, as well as photoluminescence (PL) spectrum, is observed with the reduced size of the perovskite QDs due to strong quantum confinement. The CH3NH3PbI3 QD with average size ∼1.7 nm exhibits ∼47 nm blue shift in the PL spectra, ∼43 fold enhancement in PL intensity and ∼25% PL quantum yield (QY). On the other hand, CH3NH3PbBr3 QD of similar size exhibits dramatically enhanced (∼124 times) PL emission with narrow line width and a PLQY of ∼57%, which is significant for the template-assisted growth of perovskite QDs film. The quantitative analysis of the PL emission Energy vs QD size shows an excellent fit with the Brus equation confirming the strong quantum confinement effect in the perovskite QDs. Analysis of low-temperature PL spectra reveals very high Exciton Binding Energy (162–272 meV) for the QDs as compared to the bulk film (32 meV) due to the high effective dielectric constant, and high electron-hole recombination probability in the QDs, which is consistent with the extremely high PLQY and stable emission from the QDs. The blue shift of the PL peak with increasing temperature is explained on the basis of localization effect. Time-resolved PL analysis for both the perovskite QDs reveals faster life time compared to their bulk counterparts, confirming the significant radiative recombination of carriers in the QDs at the room temperature. The CH3NH3PbBr3 QDs embedded in porous F-TiO2 template maintain its initial PL intensity up to several hours (≥10 h) under the UV laser exposure (18mW), while that of the bulk film decreases to

Weidong Sheng - One of the best experts on this subject based on the ideXlab platform.

  • Excitonic absorption spectra in graphene nanoflakes tuning of Exciton Binding Energy by dielectric environments
    Journal of Chemical Physics, 2017
    Co-Authors: Hao Wang, Weidong Sheng
    Abstract:

    By solving the Bethe-Salpeter equation within the Hartree-Fock formalism, we study the Excitonic absorption spectra of graphene nanoflakes embedded in various dielectric environments. With the Excitonic effects fully taken into account, the Exciton Binding Energy as a function of the dielectric constant is found to be well described by a single scaling rule in which the scaling factor is found to vary slowly with the size of the nanoflakes. Furthermore, it is revealed that the Exciton Binding Energy scales almost linearly with the on-site interaction Energy and exhibits more sensitive dependence in smaller nanoflakes. Our results are found to agree well with the recent experiment.

  • influence of electron hole so phonon coupling on the Exciton Binding Energy in quantum wires
    Solid State Communications, 1993
    Co-Authors: Weidong Sheng
    Abstract:

    Abstract The Exciton Binding Energy, as well as the two corrections which is due to the electron(hole)-SO-phonon interaction, in free-standing quantum-well wires with circular cross section is calculated by using of variational solutions to the effective-mass equation. The unexpected results are obtained: Although electron(hole)-SO-phonon coupling is much stronger in Q1D systems, it has little influence on the Exciton Binding Energy.

Graham R Fleming - One of the best experts on this subject based on the ideXlab platform.

  • Exciton Binding Energy in semiconducting single walled carbon nanotubes
    Journal of Physical Chemistry B, 2005
    Co-Authors: Leonas Valkunas, Sergei M Bachilo, Graham R Fleming
    Abstract:

    The Exciton Binding Energy serves as a critical criterion for identification of the nature of elementary excitations (neutral Excitons versus a pair of charged carriers) in semiconductor materials. An Exciton Binding Energy of 0.41 eV is determined experimentally for a selected nanotube type, the (8,3) tube, confirming the Excitonic nature of the elementary excitations. This determination is made from the Energy difference between an electron-hole continuum and its precursor Exciton. The electron-hole continuum results from dissociation of Excitons following extremely rapid Exciton-Exciton annihilation and possibly also ultrafast relaxation from the second to the first Exciton states and is characterized by distinct spectroscopic and dynamic signatures.

Alexander Polizzotti - One of the best experts on this subject based on the ideXlab platform.

  • a site cation in inorganic a3sb2i9 perovskite influences structural dimensionality Exciton Binding Energy and solar cell performance
    Chemistry of Materials, 2018
    Co-Authors: Juanpablo Correabaena, Rachel C Kurchin, Nathan D Klein, Lea Nienhaus, Noor Titan Putri Hartono, Mariya Layurova, Seong Sik Shin, Jeremy R Poindexter, Sarah Wieghold, Alexander Polizzotti
    Abstract:

    Inspired by the rapid rise in efficiencies of lead halide perovskite (LHP) solar cells, lead-free alternatives are attracting increasing attention. In this work, we study the photovoltaic potential of solution-processed antimony (Sb)-based compounds with the formula A3Sb2I9 (A = Cs, Rb, and K). We experimentally determine bandgap magnitude and type, structure, carrier lifetime, Exciton Binding Energy, film morphology, and photovoltaic device performance. We use density functional theory to compute the equilibrium structures, band structures, carrier effective masses, and phase stability diagrams. We find the A-site cation governs the structural and optoelectronic properties of these compounds. Cs3Sb2I9 has a 0D structure, the largest Exciton Binding Energy (175 ± 9 meV), an indirect bandgap, and, in a solar cell, low photocurrent (0.13 mA cm–2). Rb3Sb2I9 has a 2D structure, a direct bandgap, and, among the materials investigated, the lowest Exciton Binding Energy (101 ± 6 meV) and highest photocurrent (1....

  • A‑Site Cation in Inorganic A3Sb2I9 Perovskite Influences Structural Dimensionality, Exciton Binding Energy, and Solar Cell Performance
    2018
    Co-Authors: Juan-pablo Correa-baena, Rachel C Kurchin, Nathan D Klein, Lea Nienhaus, Noor Titan Putri Hartono, Mariya Layurova, Seong Sik Shin, Jeremy R Poindexter, Sarah Wieghold, Alexander Polizzotti
    Abstract:

    Inspired by the rapid rise in efficiencies of lead halide perovskite (LHP) solar cells, lead-free alternatives are attracting increasing attention. In this work, we study the photovoltaic potential of solution-processed antimony (Sb)-based compounds with the formula A3Sb2I9 (A = Cs, Rb, and K). We experimentally determine bandgap magnitude and type, structure, carrier lifetime, Exciton Binding Energy, film morphology, and photovoltaic device performance. We use density functional theory to compute the equilibrium structures, band structures, carrier effective masses, and phase stability diagrams. We find the A-site cation governs the structural and optoelectronic properties of these compounds. Cs3Sb2I9 has a 0D structure, the largest Exciton Binding Energy (175 ± 9 meV), an indirect bandgap, and, in a solar cell, low photocurrent (0.13 mA cm–2). Rb3Sb2I9 has a 2D structure, a direct bandgap, and, among the materials investigated, the lowest Exciton Binding Energy (101 ± 6 meV) and highest photocurrent (1.67 mA cm–2). K3Sb2I9 has a 2D structure, intermediate Exciton Binding energies (129 ± 9 meV), and intermediate photocurrents (0.41 mA cm–2). Despite remarkably long lifetimes in all compounds (54, 9, and 30 ns for Cs-, Rb-, and K-based materials, respectively), low photocurrents limit performance of all devices. We conclude that carrier collection is limited by large Exciton Binding energies (experimentally observed) and large carrier effective masses (calculated from density functional theory). The highest photocurrent and efficiency (0.76%) were observed in the Rb-based compound with a direct bandgap, relatively lower Exciton Binding Energy, and lower calculated electron effective mass. To reliably screen for candidate lead-free photovoltaic absorbers, we advise that faster and more accurate computational tools are needed to calculate Exciton Binding energies and effective masses

Nobutsugu Minami - One of the best experts on this subject based on the ideXlab platform.

  • photocurrent quantum yield of semiconducting carbon nanotubes dependence on excitation Energy and Exciton Binding Energy
    Journal of Physical Chemistry C, 2014
    Co-Authors: Said Kazaoui, Steffan Cook, Nicolas Izard, Yoichi Murakami, Shigeo Maruyama, Nobutsugu Minami
    Abstract:

    We address the dependence of the relative photocurrent quantum yield (QY) on the excitation Energy and the Exciton Binding Energy of semiconducting single-walled carbon nanotubes (s-SWNTs) having well-defined chiral indexes, by analyzing both the optical absorption and the photocurrent spectra. First, we examine the QY of a sample consisting of one sort of nanotube (such as (7,5)), which allows revealing that QY depends on the excitation Energy and hence on the nature of the electronic transition. In particular, we demonstrate that the QY of the second Excitonic transition (E22) is relatively higher than that of the first Excitonic transition (E11). Then, we extend the analysis to a sample consisting of five kinds of nanotubes (namely, (7,5), (7,6), (8,6), (8,7), (9,7)), which permits demonstrating for the first time that QY increases with increasing the nanotube’s diameter and with decreasing the Exciton Binding Energy, according to two categories known as type 1 and type 2 nanotubes. Finally, we discuss...