Comparison between Trion and Exciton Electronic Properties in CdSe and PbS Nanoplatelets
07 Jul 2021-Journal of Physical Chemistry C (American Chemical Society (ACS))-Vol. 125, Iss: 28, pp 15614-15622
TL;DR: In this paper, the authors analyzed how the presence of an additional charge in trions modifies the emission energy and oscillator strength as compared to neutral excitons and observed that both negative and positive trions are redshifted with respect to the exciton, and their emission energy increases with increasing dielectric mismatch between the platelet and its surroundings.
Abstract: The optoelectronic properties of metal chalcogenide colloidal nanoplatelets are often interpreted in terms of excitonic states. However, recent spectroscopic experiments evidence the presence of trion states, enabled by the slow Auger recombination in these structures. We analyze how the presence of an additional charge in trions modifies the emission energy and oscillator strength as compared to neutral excitons. These properties are very sensitive to dielectric confinement and electronic correlations, which we describe accurately using image-charge and variational Quantum Monte Carlo methods in effective mass Hamiltonians. We observe that the giant oscillator strength of neutral excitons is largely suppressedin trions. Both negative and positive trions are redshifted with respect to the exciton, and their emission energy increases with increasing dielectric mismatch between the platelet and its surroundings, which is a consequence of the self-energy potential. Our results are consistent with experiments in the literature, and assess on the validity of previous theoretical approximations.
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01 Jan 2004
TL;DR: Wurtzite Cadmium Sulphide (w-CdS).- Cubic CdS (c-cdS) as mentioned in this paper.- Wurtzeite CadMium Selenide (WurtZite CdSe), Wurtziite Zinc Oxide (ZnO).
Abstract: Magnesium Oxide (MgO).- Zincblende Magnesium Sulphide (?-MgS).- Zincblende Magnesium Selenide (?-MgSe).- Zincblende Magnesium Telluride (?-MgTe).- Zinc Oxide (ZnO).- Wurtzite Zinc Sulphide (?-ZnS).- Cubic Zinc Sulphide (?-ZnS).- Zinc Selenide (ZnSe).- Zinc Telluride (ZnTe).- Cubic Cadmium Sulphide (c-CdS).- Wurtzite Cadmium Sulphide (w-CdS).- Cubic Cadmium Selenide (c-CdSe).- Wurtzite Cadmium Selenide (w-CdSe).- Cadmium Telluride (CdTe).- Cubic Mercury Sulphide (?-HgS).- Mercury Selenide (HgSe).- Mercury Telluride (HgTe).
277 citations
TL;DR: The field of colloidal synthesis of semiconductors emerged 40 years ago and has reached a certain level of maturity thanks to the use of nanocrystals as phosphors in commercial displays as mentioned in this paper .
Abstract: The field of colloidal synthesis of semiconductors emerged 40 years ago and has reached a certain level of maturity thanks to the use of nanocrystals as phosphors in commercial displays. In particular, II-VI semiconductors based on cadmium, zinc, or mercury chalcogenides can now be synthesized with tailored shapes, composition by alloying, and even as nanocrystal heterostructures. Fifteen years ago, II-VI semiconductor nanoplatelets injected new ideas into this field. Indeed, despite the emergence of other promising semiconductors such as halide perovskites or 2D transition metal dichalcogenides, colloidal II-VI semiconductor nanoplatelets remain among the narrowest room-temperature emitters that can be synthesized over a wide spectral range, and they exhibit good material stability over time. Such nanoplatelets are scientifically and technologically interesting because they exhibit optical features and production advantages at the intersection of those expected from colloidal quantum dots and epitaxial quantum wells. In organic solvents, gram-scale syntheses can produce nanoparticles with the same thicknesses and optical properties without inhomogeneous broadening. In such nanoplatelets, quantum confinement is limited to one dimension, defined at the atomic scale, which allows them to be treated as quantum wells. In this review, we discuss the synthetic developments, spectroscopic properties, and applications of such nanoplatelets. Covering growth mechanisms, we explain how a thorough understanding of nanoplatelet growth has enabled the development of nanoplatelets and heterostructured nanoplatelets with multiple emission colors, spatially localized excitations, narrow emission, and high quantum yields over a wide spectral range. Moreover, nanoplatelets, with their large lateral extension and their thin short axis and low dielectric surroundings, can support one or several electron-hole pairs with large exciton binding energies. Thus, we also discuss how the relaxation processes and lifetime of the carriers and excitons are modified in nanoplatelets compared to both spherical quantum dots and epitaxial quantum wells. Finally, we explore how nanoplatelets, with their strong and narrow emission, can be considered as ideal candidates for pure-color light emitting diodes (LEDs), strong gain media for lasers, or for use in luminescent light concentrators.
9 citations
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TL;DR: In this paper, the authors used radiative Auger on trions in single quantum dots to determine the quantisation energies of a single electron, which can be used for other semiconductor nanostructures and colour centres.
Abstract: In a multi-electron atom, an excited electron can decay by emitting a photon. Typically, the leftover electrons are in their ground state. In a radiative Auger process, the leftover electrons are in an excited state and a red-shifted photon is created. In a quantum dot, radiative Auger is predicted for charged excitons. For a singly-charged trion, a photon is created on electron-hole recombination, leaving behind a single electron. Radiative Auger determines the quantisation energies of this single electron, information which is otherwise difficult to acquire. For this reason, radiative Auger is a powerful tool. However, radiative Auger has not been observed on single quantum dots. Here, we report radiative Auger on trions in single quantum dots. There are sharp red-shifted emission lines with intensities as high as 1% of the main emission enabling the single-electron quantisation energies to be measured with high precision. Going beyond the original proposals, we show how quantum optics -- an analysis of the photon correlations -- gives access to the single-electron dynamics, notably relaxation and tunneling. All these properties of radiative Auger can be exploited on other semiconductor nanostructures and colour centres.
8 citations
TL;DR: In this paper , a variational Quantum Monte Carlo model was proposed to evaluate the biexciton ground state properties in colloidal CdSe nanoplatelets. And the model was used to provide theoretical assessment on the ground-state properties of colloidal cdSe nanostructures.
Abstract: Biexciton properties in semiconductor nanostructures are highly sensitive to quantum confinement, relative electron-hole masses, dielectric environment and Coulomb correlations. Here we present a variational Quantum Monte Carlo model which, coupled to effective mass Hamiltonians, takes into account all of the above effects. The model is used to provide theoretical assessment on the biexciton ground state properties in colloidal CdSe nanoplatelets. A number of characteristic features is observed: (i) the finite thickness of these systems makes the biexciton geometry depart from the planar square expected in the two-dimensional (2D) limit, and form a distorted tetrahedron instead; (ii) the strong dielectric confinement enhances not only Coulomb attractions but also repulsions, which lowers the ratio of the biexciton-to-exciton binding energy down to EXXb/EXb = 0.07. (iii) EXXb is less sensitive than EXb to lateral confinement, and yet it can reach values above 30 meV, thus granting room temperature stability; (iv) the ratio of biexciton-to-exciton radiative rates, kradXX/kradX, decreases from 3.5 to ∼1 as the platelet area increases. These results pave the way for the rational design of biexciton properties in metal chalcogenide nanoplatelets.
7 citations
TL;DR: In this paper , the authors provide a timely review to survey the physical phenomena and laws involved in single-molecule optoelectronic materials and devices, including charge effects, spin effects, exciton effects, vibronic effects, structural and orbital effects.
Abstract: Single-molecule optoelectronic devices promise a potential solution for miniaturization and functionalization of silicon-based microelectronic circuits in the future. For decades of its fast development, this field has made significant progress in the synthesis of optoelectronic materials, the fabrication of single-molecule devices and the realization of optoelectronic functions. On the other hand, single-molecule optoelectronic devices offer a reliable platform to investigate the intrinsic physical phenomena and regulation rules of matters at the single-molecule level. To further realize and regulate the optoelectronic functions toward practical applications, it is necessary to clarify the intrinsic physical mechanisms of single-molecule optoelectronic nanodevices. Here, we provide a timely review to survey the physical phenomena and laws involved in single-molecule optoelectronic materials and devices, including charge effects, spin effects, exciton effects, vibronic effects, structural and orbital effects. In particular, we will systematically summarize the basics of molecular optoelectronic materials, and the physical effects and manipulations of single-molecule optoelectronic nanodevices. In addition, fundamentals of single-molecule electronics, which are basic of single-molecule optoelectronics, can also be found in this review. At last, we tend to focus the discussion on the opportunities and challenges arising in the field of single-molecule optoelectronics, and propose further potential breakthroughs.
5 citations
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517 citations