HgS硫化汞的光吸收截面

No abstract

HgTe colloidal quantum dots (QDs) are of interest because quantum confinement of semimetallic bulk HgTe allows one to synthetically control the bandgap throughout the infrared. Here, we synthesize highly monodisperse HgTe QDs and tune their doping both chemically and electrochemically. The monodispersity of the QDs was evaluated using small-angle X-ray scattering (SAXS) and suggests a diameter distribution of ∼10% across multiple batches of different sizes. Electron-doped HgTe QDs display an intraband absorbance and bleaching of the first two excitonic features. We see splitting of the intraband peaks corresponding to electronic transitions from the occupied 1S_e state to a series of nondegenerate 1P_e states. Spectroelectrochemical studies reveal that the degree of splitting and relative intensity of the intraband features remain constant across doping levels up to two electrons per QD. Theoretical modeling suggests that the splitting of the 1P_e level arises from spin-orbit coupling and reduced QD symmetry. The fine structure of the intraband transitions is observed in the ensemble studies due to the size uniformity of the as-synthesized QDs and strong spin-orbit coupling inherent to HgTe.

No abstract

The National Standard Reference Data System was established in 1963 for the purpose of promoting the critical evaluation and dis- semination of numerical data of the physical sciences.The program is coordinated by the Office of Standard Reference Data of the National Bureau of Standards, but Involves the efforts of many groups in universities, government laboratories, and private industry.The primary aim of the program is to provide compilations of critically evaluated numerical data.These tables are published in the Journal of Physical and Chemical Reference Data , The NSRDS-NBS Publication Series of the National Bureau of Standards, and through other appropriate channels.The present report consists of tables of data assembled for use in modelling the chemistry of the stratosphere.It represents contributions from the Chemical Kinetics Information Center, other NSRDS data centers, and a number of individual experts.Support for the preparation of those tables has been provided by the Department of Transportation under the High Altitude Pollution Program, by the

The National Standard Reference Data System provides effective access to the quantitative data of physical science, critically evaluated and compiled for convenience, and readily accessible through a variety of distribution channels. The System was established in 1963 by action of the President's Office of Science and Technology and the Federal Council for Science and Technology, with responsibility to administer it assigned to the National Bureau of Standards.

In cinnabar ($\ensuremath{\alpha}$-HgS) grown by chemical vapor transport (CVT), four photoluminescence (PL) features, ${X}_{1}$, ${X}_{2}$, ${B}_{1}$, and ${B}_{2}$, are observed with below band-gap photoexcitation. Two of these PL features, ${X}_{1}$ at 1.873 eV and ${X}_{2}$ at 1.855 eV, are sharp, with half-widths of 3.7 and 6.6 meV, respectively, and two of them, ${B}_{1}$ at 2.19 eV and ${B}_{2}$ at 1.78 eV, are broad, with half-widths of \ensuremath{\sim} 100 meV. New photoluminescence, optical absorption, and PL excitation measurements are reported on this material. The details observed in these measurements, together with transport results, enable presentation of an energy-level scheme and Fermi-level assignment for CVT-grown cinnabar which accounts for the ${X}_{1}$, ${X}_{2}$, ${B}_{1}$, and ${B}_{2}$ PL features. In addition to the valence- and conduction-band continua, five energy states are postulated, three levels nearer to the conduction band and two levels nearer to the valence band. The binding energies of the former are 0.005, 0.402, and 0.420 eV, and those of the latter are 0.25 and 0.05 eV. Based upon PL excitation spectra and optical absorption, ${\ensuremath{\epsilon}}_{F}$, the equilibrium Fermi energy, is placed in the range $1.855\ensuremath{\lesssim}{\ensuremath{\epsilon}}_{F}\ensuremath{\lesssim}1.873$ eV. In order to explain the shape of the optical absorption and PL excitation spectra, matrix-element effects are examined for a very simple band-to-impurity absorption process. The two PL features ${X}_{1}$ and ${X}_{2}$ can be interpreted as bound-to-free transitions which are weakly coupled to lattice vibrations, whereas the ${B}_{1}$ and ${B}_{2}$ features can be interpreted as bound-to-bound transitions strongly coupled to lattice vibrations. The temperature dependence of the ${X}_{1}$ and ${B}_{2}$ peak intensities is discussed in terms of a configuration coordinate model. The linear broadening of the ${X}_{1}$ and ${X}_{2}$ peaks with temperature above \ensuremath{\sim} 20 K is attributed to interactions with phonons.

No abstract

No abstract

We report the first positive experimental observation of the optical activity effect on normal reflection. The experiment was performed along the optic axis in a gyrotropic semiconductor crystal of \ensuremath{\alpha}-HgS, cinnabar, in a spectral region of strong absorption. Reflected light polarization azimuth rotation resulting from the reflection is in the order of ${10}^{\mathrm{\ensuremath{-}}4}$ rad and has pronounced dependence on \ensuremath{\Elzxh}\ensuremath{\omega}-${\mathit{E}}_{\mathit{g}}$.

No abstract

A theoretical discussion is given of infrared detection systems employing an optically nonlinear crystal, a laser in the visible, and photomultiplier to detect the light produced at the sum or difference frequency. Three optical mixing systems are considered in detail and compared with direct detection: (a) cinnabar (HgS) in a single-pass optical system with the He–Ne 0.6328 μm cw laser, (b) the same crystal and laser with a ring resonator and narrow-band output filter, and (c) an ideal resonant system with a crystal as nonlinear as HgS but without absorption or double refraction. The noise output consisting of up-converted thermal noise and (in the case of the difference frequency) optical parametric noise is computed quantitatively. These systems have too small a quantum efficiency to compete with a heterodyne system employing an ir laser and a detector of high quantum efficiency such as a Ge:Cu-cooled photoconductor. The Ge:Cu detector has however a large dark noise compared to a good photomultiplier, and consequently optical mixing can surpass nonheterodyne direct detection if the required value of B≡(S/N)Δf is sufficiently small. The range of superiority of optical mixing over nonheterodyne direct detection extends high enough in B for Morse code for system (a) (if sum frequency is used), nearly high enough for a telephone channel for (b) and up to the television level for (c).

Summary The results of measurements of diffuse reflectance over the wavelength range 200 < λ < 2500 nm are reported for sphalerite, cinnabar, alabandite, chalcopyrite, bornite, orpiment, stibnite, bismuthinite, enargite, and pyrargyrite, and for eight pyrite-type and four NiAs-type compounds. Some spectral assignments have been made. Optical properties are related to the absorption spectrum (and through this to composition and structure) in a rational way. Absolute reflectances tend to increase with mean atomic number (z) through the operation of the ‘z-sum rule’, and at constant z they decrease as the band gap increases. Bireflectance is structurally controlled, being weak in derivatives of the cubic sphalerite and pyrite structures, moderate in derivatives of wurtzite and NiAs, and strong in anisodesmic structures such as that of stibnite. Extreme bireflectance occurs in anisodesmic structures with strong dichroic absorption bands in the visible (molybdenite, covelline). The dispersion of reflectance (dR/dλ) depends on the position of the centre of the main absorption envelope in relation to the visible spectrum. For λ > , dispersion is normal ( R blue > R red , d R /dλ negative), the streak is light or coloured, and polished surfaces tend to be bluish. For λ < , dispersion is reversed ( R red > R blue ), the streak is dark, and polished surfaces are yellowish. Polished surfaces are white or grey if absorption varies little through the visible or strongly coloured if it varies rapidly (covelline, chalcopyrite).

Mercury sulfide (HgS) nanoparticles (NPs) were prepared in the presence of water-soluble thiols as capping ligands in aqueous solutions. Chiral thiol ligands successfully afforded the formation of the chiral cinnabar phase (α-HgS), leading to optically active NPs, while two achiral thiols preserved β-HgS NPs with an achiral crystalline system. The profiles of UV-vis absorption and circular dichroism (CD) spectra of chiral NPs were dependent on the chemical structures of the chiral ligands. Cysteine-based derivatives gave HgS NPs demonstrating almost mirror image CD profiles even though they possess identical stereochemistry. The water soluble chiral ligands on the NPs were replaced with an achiral ligand, 1-dodecanethiol, by the spontaneous phase transfer method. The ligand-exchanged NPs with the achiral thiol preserved the optical activity with a feature of the CD profile similar to that of the original NPs in water, demonstrating the chiral memory effect in the NP-core. The dissymmetry factor in optical absorption decreased by almost half, which could be attributed to the amorphous phase formed by the chemical etching with an excess amount of dodecanethiol. The optical activity showed a higher thermal stability compared to that of NPs before the ligand-exchange.

We report ab initio calculations of the electronic band structure, the corresponding optical spectra, and the phonon dispersion relations of trigonal $\ensuremath{\alpha}\text{-HgS}$ (cinnabar). The calculated dielectric functions are compared with unpublished optical measurements by [Zallen et al. (unpublished)] The phonon dispersion relations are used to calculate the temperature and isotopic mass dependence of the specific heat which has been compared with experimental data obtained on samples with the natural isotope abundances of the elements Hg and S (natural minerals and vapor phase grown samples) and on samples prepared from isotope enriched elements by vapor phase transport. Comparison of the calculated vibrational frequencies with Raman and ir data is also presented. Contrary to the case of cubic $\ensuremath{\beta}\text{-HgS}$ (metacinnabar), the spin-orbit splitting of the top valence bands at the $\ensuremath{\Gamma}$ point of the Brillouin zone $({\ensuremath{\Delta}}_{0})$ is positive, because of a smaller admixture of $5d$ core electrons of Hg. Calculations of the lattice parameters, and the pressure dependence of ${\ensuremath{\Delta}}_{0}$ and the corresponding direct gap ${E}_{0}\ensuremath{\sim}2\text{ }\text{eV}$ are also presented. The lowest absorption edge is confirmed to be indirect.

We report on the optical properties of high pressure semiconducting phases in ZnTe 1 m x Se x . In the Te rich side, the cinnabar phase is observed in the upstroke between typically 9.5 and 12.5 GPa with a pressure interval of existence that decreases with increasing the Se content. In most studied samples, the indirect absorption edge could be determined, with values of the bandgap increasing with the Se content and ranging from 1.2 to 1.7 eV. In the downstroke, the cinnabar phase is observed in the whole composition range but its bandgap can not be unambiguously determined in the Se-rich side, as it coexists with rocksalt or zincblende phases. The indirect semiconducting rocksalt phase is observed in the Se-rich side, with an indirect bandgap of the order of 0.7 eV. Within the experimental errors, the bandgaps of both the cinnabar and NaCl phases are pressure insensitive, in agreement with first-principles pseudopotential band structure calculations, that predict very low pressure coefficients for both indirect transitions.

Abstract In this paper we report on isothermal compression measurements (up to 5 GPa and 500 K) of the optical absorption edge of 1 μm epitaxial layers of CdTe growth by metalorganic chemical vapor deposition (MOCVD) on GaS substrates. The isothermal blue shift under pressure of the direct energy gap (Γ v 15 → Γ c 1 ) in the zinc‐blende phase is about 7.1 × 10 –2 eV GPa –1 and is found to be independent of temperature within the experimental errors. The isobaric red shift in the stability range of the zinc‐blende phase is about –3.76 × 10 –4 eV K –1 . Regarding the phase transitions, no discontinuity in the energy gap has been found in the narrow pressure range where the cinnabar phase can be present. The transition pressure to the NaCl‐type structure in CdTe is found to decrease with increasing temperature (294–500 K) following the law P t = 4.1 GPa – 6.6 × 10 –3 ( T – 273) (K).

It has been demonstrated that the hydrostatic deformation potential $C\ensuremath{-}a$ of a semimetal can be determined from the pressure dependence of intersubband transitions in superlattices containing the semimetal. By means of an investigation of optical absorption in $\mathrm{Hg}\mathrm{Te}∕{\mathrm{Hg}}_{0.3}{\mathrm{Cd}}_{0.7}\mathrm{Te}$ superlattices at hydrostatic pressures up to $3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at room temperature the following values have been determined: $C\ensuremath{-}a=\ensuremath{-}3.69\ifmmode\pm\else\textpm\fi{}0.10\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and ${a}^{\mathrm{Hg}\mathrm{Te}}\ensuremath{-}{a}^{\mathrm{Cd}\mathrm{Te}}=1.31\ifmmode\pm\else\textpm\fi{}0.10\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, where $C$ and $a$ are the deformation potentials of the conduction and valence bands, respectively. Bulk HgTe normally undergoes a phase transition to the cinnabar structure at $\ensuremath{\approx}1.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. However, this phase transition is frustrated in $\mathrm{Hg}\mathrm{Te}∕{\mathrm{Hg}}_{0.3}{\mathrm{Cd}}_{0.7}\mathrm{Te}$ superlattices and the HgTe layers are superpressed above $1.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.

L'analyse des données relatives aux indices du cinabre (α-HgS) à l'aide d'une formule de Sellmeier montre que les dispersions ne(λ) et no(λ) dans le visible et le proche infrarouge sont probablement dues à une měme transition électronique d'énergie E ≈ 1,5 Eg. L'influence des vibrations ioniques est en bon accord avec les résultats de dynamique de réseau. Des mesures systématiques de biréfringence Δn = ne – no, entre 0,6 et 20 μm ont été faites pour caractériser les échantillons synthétiques; elles confirment et étendent les résultats antérieurs, en montrant toutefois que le matériau obtenu ne présente pas encore les qualités de reproductibilité nécessaires à la mise au point de dispositifs. L'analyse de la variation Δn(T) permet de préciser la dépendance en température de E et des forces d'oscillateurs associées: l'essentiel de ∂Δn/∂T est dǔ à ∂E/∂T et à l'effet implicite de la dilatation. The available data concerning ne(λ) and no(λ) of cinnabar (α-HgS) are analysed using Sellmeier dispersion-laws. The same electronic transition at E ≈ 1.5 Eg is shown to be probably responsible for the dispersion in the visible and near IR. Good agreement with the lattice dynamics studies has also been found for the influence of the ionic vibrations. Systematic birefringence (Δn = ne – no) measurements by means of a fringes-method have been performed on synthetic samples, over the whole transparency or small absorption range (0.6 to 20 μm). Presently Δn is not well definite and this non-reproductibility of the optical constant is to be overcome before making devices. Moreover the study of Δn(T) allowed to precise the T variations of some parameters; the implicit contribution of the dilatation to the oscillators strengths and ∂E/∂T are shown to be preponderant in the variation of ∂Δn/∂T = f(λ).

No abstract

Optical absorption, electron spin resonance (ESR) and nuclear (NMR) studies of silicate minerals such as quartz and topaz help to reveal the nature of a variety of colors which are derived from defects within the crystal structures involving the presence of impurities, trapped holes, and electrons. The present study was inspired by color changes in cinnabar, which upon exposure to sunlight, turns from vermillion red to black under certain conditions, the solid state physical reasons for which have not yet been described. Smoky and amethyst quartz are also bleached by energy from the Sun; reactions that can be reversed by the process of artificial irradiation and heat treatment. Topaz, the focus of this study, exhibits the imperial yellow variety from Ouro Preto, Brazil, which bleaches upon exposure to high temperatures and gives rise to a pink color if chromium is present as an impurity. For the blue variety of topaz, which arises from the irradiation of colorless topaz to smoky, then heat treating to blue, the crystal chemistry remains undefined. Many color centers found in topaz are believed to have a relationship to the presence of aluminum in tetrahedral sites, also related to trapped hole/electron defects. Although NMR studies have targeted the presence of 27Al with uncertain results, optical absorption and ESR studies show clear connections to the production of electronic defects related to absorbing centers caused by high energy irradiation. ESR studies indicate that significant information can be attained relative to these defects when the magnetic vector is parallel to the c axis of the crystal. This paper begins to shed light on the responsible mechanisms that may define the crystal chemistry in terms of the electronic environment, with particular emphasis on topaz.

Cooperative chirality phenomena extensively exist in biomolecular and organic systems via intra- and inter-molecular interactions, but study of inorganic materials has been lacking. Here we report, experimentally and theoretically, cooperative chirality in colloidal cinnabar mercury sulfide nanocrystals that originates from chirality interplay between the crystallographic lattice and geometric morphology at different length scales. A two-step synthetic scheme is developed to allow control of critical parameters of these two types of handedness, resulting in different chiral interplays expressed as observables through materials engineering. Furthermore, we adopt an electromagnetic model with the finite element method to elucidate cooperative chirality in inorganic systems, showing excellent agreement with experimental results. Our study enables an emerging class of nanostructures with tailored cooperative chirality that is vital for fundamental understanding of nanoscale chirality as well as technology applications based on new chiroptical building blocks.

Mercury sulphide (HgS) films were deposited on glass substrates by the chemical bath deposition method (CBD) at different deposition times and then post-annealed at 300°C for about 1 h. The structure of the produced films was studied by X-ray diffraction (XRD). Elemental analyses of the prepared films were characterised by the energy-dispersive X-ray analysis (EDX). The film’s optical properties were measured by spectrophotometry. The optical constants of films were derived from reflectivity curves by the Kramers–Kronig method. The absorption coefficient, extinction coefficient, refractive index, real and imaginary parts of the dielectric constant, and the optical band gaps were calculated. X-ray diffraction details showed a crystalline phase for all deposited HgS thin films with trigonal structures. Optical results exhibited photoluminescence property for HgS thin films. By increasing deposition time, the dielectric property, refractive index and band gap values are increased. The values obtained for electronic and optical properties of HgS are essentially crucial for applications in optoelectronics.

Quantum-confined nanostructures are considered 'artificial atoms' because the wavefunctions of their charge carriers resemble those of atomic orbitals. For multiple-domain heterostructures, however, carrier wavefunctions are more complex and still not well understood. We have prepared a unique series of cation-exchanged Hg(x)Cd(1-x)Te quantum dots (QDs) and seven epitaxial core-shell QDs and measured their first and second exciton peak oscillator strengths as a function of size and chemical composition. A major finding is that carrier locations can be quantitatively mapped and visualized during shell growth or cation exchange simply using absorption transition strengths. These results reveal that a broad range of quantum heterostructures with different internal structures and band alignments exhibit distinct carrier localization patterns that can be used to further improve the performance of optoelectronic devices and enhance the brightness of QD probes for bioimaging.

No abstract

The degradation of colors in historical paintings affects our cultural heritage in both museums and archeological sites. Despite intensive experimental studies, the origin of darkening of one of the most ancient pigments known to humankind, vermilion (α-HgS), remains unexplained. Here, by combining many-body theoretical spectroscopy and high-resolution microscopic x-ray diffraction, we clarify the composition of the damaged paint work and demonstrate possible physicochemical processes, induced by illumination and exposure to humidity and air, that cause photoactivation of the original pigment and the degradation of the secondary minerals. The results suggest a new path for the darkening process which was never considered by previous studies and prompt a critical examination of their findings.

Hg-based chalcogenides, as good candidates for the exploration of high-performance infrared (IR) nonlinear optical (NLO) materials, usually exhibit strong NLO effects, but narrow bandgaps. Herein, an unprecedented wide bandgap Hg-based IR NLO material Zn₂ HgP₂ S₈ (ZHPS) with diamond-like structure is rationally designed and fabricated by a tetrahedron re-organization strategy with the aid of structure and property predictions. ZHPS exhibits a wide bandgap of 3.37 eV, which is the largest one among the reported Hg-based chalcogenide IR NLO materials and first breaks the 3.0 eV bandgap "wall" in this system, resulting in a high laser-induced damage threshold (LIDT) of ≈2.2 × AgGaS₂ (AGS). Meanwhile, it shows a large NLO response (1.1 × AGS), achieving a good balance between bandgap (≥3.0 eV) and NLO effect (≥1 × AGS) for an excellent IR NLO material. DFT calculations uncover that, compared to normal [HgS₄ ]_n , highly distorted [HgS₄ ]_d tetrahedral units are conducive to generating wide bandgap, and the wide bandgap in ZHPS can be attributed to the strong s-p hybridization between Hg─S bonding in distorted [HgS₄ ]_d , which gives some insights into the design of Hg-based chalcogenides with excellent properties based on distorted [HgS₄ ]_d tetrahedra.

No abstract

In this work, we report on high-pressure Raman scattering measurements in mercury digallium sulfide (HgGa2S4) with defect chalcopyrite structure that have been complemented with lattice dynamics ab initio calculations. Our measurements evidence that this semiconductor exhibits a pressure-induced phase transition from the completely ordered defect chalcopyrite structure to a partially disordered defect stannite structure above 18 GPa which is prior to the transition to the completely disordered rocksalt phase above 23 GPa. Furthermore, a completely disordered zincblende phase is observed below 5 GPa after decreasing pressure from 25 GPa. The disordered zincblende phase undergoes a reversible pressure-induced phase transition to the disordered rocksalt phase above 18 GPa. The sequence of phase transitions here reported for HgGa2S4 evidence the existence of an intermediate phase with partial cation-vacancy disorder between the ordered defect chalcopyrite and the disordered rocksalt phases and the irreversibility of the pressure-induced order-disorder processes occurring in ordered-vacancy compounds. The pressure dependence of the Raman modes of all phases, except the Raman-inactive disordered rocksalt phase, have been measured and discussed.

Nonlinear optical (NLO) crystals are widely used in advanced photonic technologies for second harmonic and difference frequency generation (SHG and DFG, respectively), producing coherent light at frequencies where existing lasers are unavailable. Isotropic glasses do not exhibit SHG or DFG, except temporarily induced anisotropy under external stimuli. However, recent reports on glasses with chiral structural motifs show promising permanent NLO properties. We propose an alternative solution: hybrid molecular/network glasses with noncentrosymmetric HgI2 monomers. Mercury(II) iodide consists of linear HgI2 triatomic molecules in the vapor phase and in the yellow orthorhombic polymorph stable above 400 K. At lower temperatures, the tetragonal red form is composed of corner-sharing HgI4/2 tetrahedra forming a layered extended framework. There is a gap in the molecular evolution; direct structural measurements of the liquid HgI2 phase are missing. Using high-energy X-ray scattering, pulsed neutron diffraction, and Raman spectroscopy supported by structural and vibrational modeling, we show that the mercury(II) iodide melt and HgI2-containing sulfide glasses are built up by bent HgI2 monomers (the bond angle ∠I–Hg–I = 156 ± 2° in the melt). The noncentrosymmetric entities imply intrinsic optical nonlinearity of the second order, confirmed by a strong SHG response.

Epitaxial growth in a CdS/HgS heterostructure of nanometer dimensions, prepared by methods of wet chemistry, is demonstrated. High-resolution transmission-electron microscopy is used to determine the shape and crystallinity of this system consisting of a quantum well in a quantum dot. The homogeneous absorption and fluorescence spectra are investigated by transient hole burning and fluorescence line-narrowing spectroscopy. The photophysical measurements provide evidence for charge-carrier localization within the HgS well.

HgS nanocrystals show a strong mid-infrared absorption and a bleach of the near-infrared band edge, both tunable in energy and reversibly controlled by exposure to solution ions under ambient conditions. The same effects are obtained by applying a reducing electrochemical potential, confirming that the mid-infrared absorption is the intraband transition of the quantum dot. This is the first time that stable carriers are present in the quantum state of strongly confined quantum dot in ambient conditions. The mechanism by which doping is achieved is attributed to the rigid shifts of the valence and conduction band with respect to the environment, similar to the sensitivity of the work function of surfaces to adsorbates.

HgS colloidal quantum dots (CQDs) are synthesized at room temperature using a dual-phase method. The HgS CQDs ranging from 3 to 15 nm exhibit air-stable n-doping and infrared intraband absorptions. For HgS CQDs of small sizes, the doping density is close to 2 electrons per dot, while for larger ones, their intraband absorption peaks shift to as far as 10 μm and exhibit Lorentzian line shapes. Under reducing potentials, these long-wavelength absorption peaks increase in strength and blue shift. This behavior can be explained through a classical model of the local field, showing how the degenerate single-electron transitions shift to a frequency that is the quadratic mean of the individual transition and a surface plasmon coming from a number of oscillators. This indicates that the intraband absorption of large, n-doped HgS CQDs is therefore becoming a surface plasmon. The same synthetic method works for HgS/CdS core/shells. Encapsulating HgS in a CdS shell removes the natural n-doping of the HgS cores, resulting in an interband photoluminescence at 1.5 μm with ∼5% quantum yield. The n-doping partially recovers upon film formation, and increases in strength after ligand exchange and annealing. The core/shell greatly improves the thermal stability of the HgS cores, allowing an annealing temperature as high as 200 °C.

We report on the first chemically prepared multilayer quantum well structure in a semiconductor quantum dot. By subsequent precipitation of HgS, CdS, HgS, and again CdS from aqueous solution, we obtained nanoparticles which contain two HgS quantum wells separated by a double layer of CdS. The core and the capping material is also CdS. The two-well system was characterized by absorption and emission spectroscopy, which clearly reveal the formation of a two-well and not a single double-layered quantum well system. This system allows to study the interaction of quantum wells that are separated by different thicknesses of the CdS barriers. The radiative and relaxation dynamics of the new two-well system are compared with the dynamics of systems having a single-layer well and a double-layer well system.

The synthesis of II-VI semiconductor nanoparticles obtained by the thermolysis of certain group 12 metal complexes as precursors is reported. Thermogravimetric analysis of the single source precursors showed sharp decomposition leading to their respective metal sulfides. The structural and optical properties of the prepared nanoparticles were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) UV-Vis and photoluminescence spectroscopy. The X-ray diffraction pattern showed that the prepared ZnS nanoparticles have a cubic sphalerite structure; the CdS indicates a hexagonal phase and the HgS show the presence of metacinnabar phase. The TEM image demonstrates that the ZnS nanoparticles are dot-shaped, the CdS and the HgS clearly showed a rice and spherical morphology respectively. The UV-Vis spectra exhibited a blue-shift with respect to that of the bulk samples which is attributed to the quantum size effect. The band gap of the samples have been calculated from absorption spectra and werefound to be about 4.33 eV (286 nm), 2.91 eV (426 nm) and 4.27 eV (290 nm) for the ZnS, CdS and HgS samples respectively.

Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440−740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.

High-quality colloidal mercury sulfide quantum dots (QDs) are synthesized at room temperature using a strategy combining the effects of strongly binding Hg(II) ligands and metal/chalcogen precursor phase separation. This combination prevents both the rapid precipitation of bulk HgS in preparations involving only weak Hg(II) ligands and the reduction of mercury that takes place when only strongly binding ligands are used to slow the growth kinetics. Both the linear absorption and complementary band edge emission of the synthesized HgS QDs exhibit narrow, size-dependent transitions between 500 and 800 nm for sizes ranging from 1 to 5 nm in diameter. The metastable zinc blende phase of HgS is verified by wide-angle X-ray diffraction experiments and suggests potentially large tunable band edges if larger HgS nanocrystals that approach the bulk (zero energy) gap can be made. Growth of HgS QDs can be arrested by subsequent addition of Cd or Zn to the surface, after which the QDs can be stabilized with long-chain thiols or amines.

No abstract

Five-layered nanocrystals have been prepared that consist of a CdS core covered by a shell of HgS followed by several monolayers of CdS that are covered by again a shell of HgS and an outer cladding layer of CdS. The resulting quantum dots, thus, contain a double well electronic structure. Both HgS wells are either as thick as a monolayer or as two monolayers. The wells are separated by a wall of two to three monolayers of CdS giving rise to a family of double well semiconductor quantum dots. Absorption spectra of eight members of this family are presented together with some first results from TEM measurements.

Electron occupation in the lowest quantized state of the conduction band (1Se) in the colloidal quantum dot leads to the intraband transition in steady-state (1Se-1Pe). The intraband transition, solely originating from the quantum confinement effect, is the unique property of semiconducting nanocrystals. To achieve the electron occupation in 1Se state in the absence of impurity ions, nonthiol ligand passivated HgS colloidal quantum dots are synthesized. The nonthiol ligand passivated HgS quantum dot exhibits strong steady-state intraband transition in ambient condition and enables a versatile ligand replacement to oxide, acid, and halide functional ligands, which was not achievable from conventional HgS or HgSe quantum dots. Surprisingly, the atomic ligand passivation to HgS colloidal quantum dot solution efficiently maintains the electron occupation at 1Se of HgS CQDs in ambient condition. The electron occupation in 1Se of HgS CQD solid film is controlled by surface treatment with charged ions, which is confirmed by the mid-IR intraband absorption (1Se-1Pe) intensity imaged by the FTIR microscope. Furthermore, a novel second intraband transition (1Pe-1De) is observed from the HgS CQD solid. The observation of the second intraband transition (1Pe-De) allows us to utilize the higher quantized states that were hidden for the last three decades. The use of the intraband transition with narrow bandwidth in mid-IR would enable to choose an optimal electronic transition occurring in the nanocrystal for a number of applications: wavelength-selective low-energy consuming electronics, space-communication light source, mid-infrared energy sensitized electrode and catalyst, infrared photodetector, and infrared filter.

Abstract Semiconductor nanocrystals prepared by methods of wet chemistry are similar to MBE grown quantum dots where the mobility of the charge carriers is reduced to zero dimensionality. In this paper we summarize the physics of a unique system in which the charge carriers are locally confined within a heterogeneous quantum dot. With high resolution electron microscopy we will show that epitaxial growth ot atomic layer precision is possible by methods of solution chemistry leading to CdS quantum dots with embedded HgS quantum wells (QDQWs). The photophysics of this system is investigated by time‐correlated single photon counting, transient differential absorption and fluorescence line narrowing spectroscopies. The results reflect the very complex electronic structure of this new kind of matter which can be explained by an extended effective mass approach.

No abstract

To design nanocrystalline nanosystems, a theory for nanocrystals is needed which can be applied to nanocrystals with atomic-scale variations in composition, structure and shape. We present an empirical tight-binding theory for nanocrystal heteronanostructures. Electronic structure and optical absorption spectra are obtained for CdS/HgS/CdS and ZnS/CdS/ZnS quantum-dot quantum-well nanocrystals. Comparison with experiment shows that tight-binding theory provides a good description of nanosystems with monolayer variations in composition. Issues for designing nanocrystal heteronanostructures are discussed.

The optical properties of different quantum dot–quantum well (QDQW) structures and of CdS-core dots have been studied utilizing photoluminescence (PL), fluorescence line narrowing (FLN), photoluminescence excitation (PLE), and double-beam PL spectroscopy. The FLN spectra of the CdS core showed resonant Raman lines, distinct from the exciton–phonon replica. The red shift of PL from the absorption edge (here “Stokes shift”) and the phonon energy in the QDQW samples differ from those in the CdS core and from HgS bulk. The Stokes shift has an inversed energy dependence in one QDQW sample compared with all others. An additional, special double beam PL experiment showed an enhancement of the excitonic band as consequence of the partial quenching of the defect band, suggesting a mutual interaction between the two luminescence events.

Subpicosecond pump−probe transient absorption spectroscopy has been used to examine the probe wavelength-dependent kinetics of PVP capped CdS/HgS/CdS quantum dot quantum well nanoparticles. Using 398- and 520-nm excitations, the relaxation of the excited hot electrons above the band gap state is characterized by both rapid electronic nonradiative relaxation and slower thermal relaxation processes. The wavelength dependence of both the fast rise and fast decay of the transient bleach is discussed in terms of electronic relaxation processes involving mixed CdS/HgS states at short probe wavelengths or pure HgS states at long probe wavelengths. The slow decay of the transient bleach is discussed in terms of a thermal relaxation process leading to the dissipation of heat from the hot nanoparticle lattice to the surrounding medium.

The femtosecond time-resolved exciton dynamics of the ${\mathrm{C}\mathrm{d}\mathrm{S}/(\mathrm{HgS})}_{2}/\mathrm{C}\mathrm{d}\mathrm{S}$ quantum-dot--quantum-well system (QDQW), which contains a double-layer HgS QW, was investigated and compared to the dynamics of the QDQW system with a single-layer HgS QW. The femtosecond hole-burning technique allowed us to resolve the energy of the different optically allowed excitonic states involved in the ultrafast relaxation pathway. The experimentally obtained exciton energies were in excellent agreement with the previously theoretically predicted values. The femtosecond time-resolved pump-probe measurements reveal a fast relaxation component of \ensuremath{\sim}5 ps at wavelengths \ensuremath{\leqslant}700 nm. At longer wavelengths, a slow decay component is found, which increases in decay time with increasing wavelength. The fast decay component (5 ps) was attributed to an energy relaxation process of the two ${1P}_{e}{\ensuremath{-}1P}_{h}$ exciton states, whereas the slow one was assigned to the decay of the dim ${1S}_{e}{\ensuremath{-}1S}_{3/2}$ state. The inhomogeneously broadened absorption band and the wide distribution of decay times in the low-energy region give strong evidence for a broad inhomogeneous energy distribution of the lowest energetic ${1S}_{e}{\ensuremath{-}1S}_{3/2}$ dim state. This is discussed in terms of the morphological structure of the quantum well.

The femtosecond time-resolved electron-hole dynamics of the CdS/HgS/CdS quantum dot--quantum well system (QDQW) was investigated as a function of excitation energy. In the transient absorption spectra four bleach bands and a stimulated emission signal in the visible spectral range between 450 and 780 nm were resolved. By using an IR probe pulse at 4.7 \ensuremath{\mu}m a transient induced absorption due to intraband transitions was found. The decay and rise times of these signals were measured when the CdS core or the HgS well of the nanoparticles was excited by the pump pulse. After excitation within the HgS well the transient signals rise within the resolution of our pump pulse, while after core excitation slower rise times were measured. From the 1.5 ps rise time of the stimulated emission originating from the HgS well and the intraband hole IR absorption (150 fs) after excitation into the CdS core, the electron localization time (transfer time from the core to the well) is found to be 1.5 ps while that of the hole is \ensuremath{\sim}150 fs. This large difference in the observed dynamics of the electron and hole in crossing the CdS/HgS interface is discussed.

We study the electronic properties of spherical quantum dot quantum well nanocrystals within a symmetry-based tight-binding model. In particular, the influence of a concentric monolayer of HgS embedded in a spherical CdS nanocrystal of diameter 52.7 Å is analyzed as a function of its distance from the center. The electron and hole states around the energy gap show a strong localization in the HgS well and the neighboring inner (core) interface region. Important effects on the optical properties such as the absorption gap and the fine structure of the exciton spectrum are also reported.

The spectrum of electrons, holes, and excitons in a superlattice composed of cylindrical quantum dots with extremely weak coupling between quasiparticles in neighboring layers of quantum dots was studied theoretically. Calculations were performed for the example of cylindrical β-HgS quantum dots embedded in β-CdS in the form of a superlattice. It is shown that electrons and holes in such a system form quasi-two-dimensional energy minibands, whereas excitons can be described in terms of the Shinoda-Sugano model. The dependence of the quasiparticle spectra on geometric parameters of a superlattice with cylindrical quantum dots was studied. It is shown that the positions of minibands for all quasiparticles are very sensitive to the height of quantum dots, which should manifest itself in the experimental excitonic absorption spectrum.

The authors report the third-harmonic generation, nonlinear refraction, and nonlinear absorption in HgS quantum dot (QD) suspensions and films using the nanosecond and femtosecond pulses. High conversion efficiency (7 × 10^-4) towards the third harmonic (TH) of the 900-1700 nm, 150 fs laser in the thin (70 nm) films containing HgS QDs deposited on the glass substrates is obtained. The authors analyze spectral dependencies of the TH, nonlinear refractive indices, and nonlinear absorption coefficients of QDs in the 500-1700 nm range and discuss the relation between the TH process and the low-order nonlinear optical properties of these quantum dots.

Abstract In between the molecular and bulk forms of matter, semiconductor nanocrystals are novel materials with interesting optical and electronic properties. We present a study of the homogeneous optical properties of two nanocrystal systems. First, the homogeneous absorption of InP nanocrystals is studied via hole burning experiments. The optical spectrum consists of a HOMO-LUMO transition with a 10 meV width and a second electronic transition shifted by 0.11 eV. The optical transitions are assigned within a three valence-band model. The CdS/HgS/CdS quantum-dot/quantum-well system is also investigated and a transmission electron microscopy study shows that the growth of the HgS well region and the CdS outer layer is epitaxial. Selective optical techniques are used to study the electronic level structure. In hole burning, a discrete transition (width of 7 meV) with pronounced phonon side bands at a frequency of 250 cm−1 is observed. In fluorescence, the line narrowed spectrum also shows phonon replicas at a similar frequency. The measurements provide direct evidence for charge localization in the low band gap HgS well region within this colloidally synthesized nano-heterostructure.

We describe the synthesis of colloidal mercury chalcogenide quantum dots (QDs) using a combination of strong Hg(II) coordinating ligands and precursor phase separation. This synthetic strategy provides a means of controlling the growth kinetics of mercury based II-VI QDs and addresses some of the problems which have heretofore made the synthesis of such compounds difficult. In particular, the simultaneous use of mercury coordinating ligands and precursor phase separation overcomes both the rapid precipitation of bulk mercury chalcogenides that occurs when only weak ligands are used and the reduction of Hg(II) when a strong ligand/high temperature combination is pursued. In the case of both HgS and HgSe this scheme has yielded one of the first examples of mercury chalcogenide QDs to date. The linear absorption/emission of HgS is size-dependent and ranges from 500 nm to 800 nm with corresponding sizes between 1 to 5 nm in diameter. For HgSe the band edge absorption/emission are also size dependent, ranging from 600 to 900 nm. The zincblende phase of both HgS and HgSe QDs is determined from wide angle x-ray diffraction experiments and reveals potentially large (band edge) spectral tunabilities for either material given their zero or slightly negative (bulk) band gaps.

Abstract We have studied the electronic structure, exciton states and optical spectra of spherical semiconductor quantum dot quantum wells (QDQW's) by means of a symmetry‐adapted tight‐binding (TB) method. We have investigated two classes of QDQW's: CdS/HgS/CdS, based on a CdS core which acts as a barrier, with a thin HgS well layer intercalated between the core and a clad layer of CdS. The second class of QDQW's is based on ZnS cores covered with CdS layers which act in this case as a well. The calculated values of the absorption onset show a good agreement with the experimental data. Large photoluminescence Stokes shifts are also predicted. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

No abstract

No abstract

Abstract Optical fibers have revolutionized the telecommunications industry to such an extent that the network capacity available today was unthinkable 20 years ago. Even so, with the advent of the datawave, and the exponential increase of network traffic predicted to continue indefinitely, the generation of bandwidth remains a challenge. One of the major limitations to the implementation of future high-capacity, ultra-broadband optical networks is the expansion of the fiber bandwidth beyond that available from the current state-of-the-art signal amplification device--the erbium-doped fiber amplifier (EDFA). Although there is currently a large effort to expand the flat-gain bandwidth of the EDFA, most of these efforts involve sophisticated engineering, exotic glass fibers, or multicomponent cascaded systems. In a radically different approach, we are attempting to use the unique properties of semiconductor nanocrystals, or quantum dots, as "designer atoms" in order to produce an ultra-broadband optical amplifier with complete coverage of the telecommunications wavelengths. In this paper we review the synthesis of thiol-stabilized mercury chalcogenide nanocrystals via an aqueous colloidal route, which demonstrate extremely intense photoluminescence all the way across the spectral region of interest, i.e., from 1000 to over 1700 nm.

No abstract

No abstract

No abstract

A novel flexible surface enhanced Raman spectroscopy (SERS) substrate was successfully fabricated by gravure printing a thin film of silver (Ag) nanoparticle ink with 20~50 nm particle size on polyethylene terephthalate (PET). The feasibility of the fabricated SERS substrate for detecting toxic heavy metals such as mercury sulfide (HgS) and cadmium sulfide (CdS) was demonstrated. The SERS based response of the printed substrate produced an enhanced Raman signal when compared to target molecules adsorbed on bare PET. An enhancement factor of 5 orders of magnitude due to existence of hot spots between nanoparticles was obtained. This response demonstrated the feasibility of the novel SERS substrate to be used in applications for detection of toxic heavy metals.

A new family of quaternary diamond-like semiconductors (DLSs), Li2HgMS4 (M = Si, Ge, Sn), were successfully discovered for the first time. All of them are isostructural and crystallize in the polar space group (Pmn21). Seen from their structures, they exhibit a three-dimensional (3D) framework structure that is composed of countless 2D honeycomb layers stacked along the c axis. An interesting feature, specifically, that the LiS4 tetrahedra connect with each other to build a 2D layer in the ac plane, is also observed. Experimental investigations show that their nonlinear optical responses are about 0.8 for Li2HgSiS4, 3.0 for Li2HgGeS4, and 4.0 for Li2HgSnS4 times that of benchmark AgGaS2 at the 55–88 μm particle size, respectively. In addition, Li2HgSiS4 and Li2HgGeS4 also have great laser-damage thresholds that are about 3.0 and 2.3 times that of powdered AgGaS2, respectively. The above results indicate that title compounds can be expected as promising IR NLO candidates.

No abstract