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The rates of multicarrier recombination are measured in colloidal quantum dots with and without hole surface trapping and with hole extraction in type II core/shell systems. We report that hole trapping or the physical separation of electronic and hole wavefunctions into different semiconductor domains of a type II system have an insignificant effect on the multicarrier recombination dynamics. These observations are inconsistent with the accepted Auger transition mechanism. [ABSTRACT FROM AUTHOR]

The interband and intraband spectra of colloidal II-VI CdS and CdSe quantum dot cores and CdS/ZnSe, CdS/CdSe, CdSe/CdS, and CdSe/ZnSe core/shell systems are reported. Infrared absorption peaks between 0.5 and 0.2 eV are observed. The slope of the intraband energy versus the first interband absorption feature is characteristic of the relative band alignments of the materials constituting the core and the shell and it is analyzed within an effective mass model. The analysis provides a new estimate of the band gap of zinc blende CdSe as well as the band offsets in zinc blende and wurtzite CdSe, CdS, and ZnSe. [ABSTRACT FROM AUTHOR]

The reduction potential of plastocyanin was determined by using the quantum mechanics/molecular mechanics (QM/MM) method. The main objective was to determine the rate of electron transfers from cytochromef to plastocyanin and from plastocyanin to p700+.

Li5AlO4, a well-known material for solid state electrolyte application, has never been considered hitherto as a gate dielectric of metal oxide thin film transistors (TFTs). Here we demonstrate the salient features of Li5AlO4 as a gate dielectric outperforming the conventional inorganic dielectrics used in TFTs. The high dielectric constant (k) of this insulator has been achieved by utilizing the improved capacitance contributed by mobile lithium ions (Li+) within the dielectric film. We have synthesized this dielectric via a cost-effective sol–gel method followed by a low-temperature annealing process yielding three phases such as amorphous-Li5AlO4 (a-Li5AlO4), α-Li5AlO4, and β-Li5AlO4 under different annealing conditions. Optimized TFTs fabricated with all of these three phases of Li5AlO4 on top of a highly doped silicon (p++-Si) wafer and a solution processed semiconducting layer of indium zinc oxide (IZO) exhibit an excellent TFT performance at different operating voltages. Among these three different types of TFTs, the device with an α-Li5AlO4 gate dielectric annealed at 500 °C shows the best device performance with an on/off ratio of 5 × 104 and an electron mobility of 21.4 ± 2.16 cm2 V−1 s−1. In addition, this device requires the least drain voltage (＜2 V) to reach the saturation drain current due to the higher Li+ mobility of the α-Li5AlO4 gate dielectric. This TFT performance on the p++-Si substrate is superior to that of a previously reported device with a sodium beta-alumina (SBA) gate dielectric, where the percentage of mobile ions within the dielectric material was comparatively much lower. Moreover, this dielectric requires ∼300 °C lower annealing temperature compared to the SBA dielectric. A metal oxide/quantum dot heterojunction phototransistor was fabricated by coating an IZO TFT with colloidal lead sulphide (PbS) quantum dots that shows a responsivity and a response time of 4.5 × 10−4 A W−1 and 2.2 s respectively. [ABSTRACT FROM AUTHOR]

We report the synthesis of copper iron sulfide (CuFeS2) quantum dots (QDs). These materials exhibit a tunable band gap that spans the range 0.5-2 eV (600-2500 nm). Although the as-prepared material is nonemissive, CuFeS2/CdS core/shell structures are shown to exhibit quantum yields that exceed 80%. Like other members of the I-III-VI2 family QDs, CuFeS2 based nanoparticles exhibit a long-lived emission that is significantly red-shifted compared to the band gap. CuFeS2 QDs are unique in terms of their composition. In particular, these QDs are the only band-gap-tunable infrared chromophore composed entirely of elements with atomic numbers less than 30. [ABSTRACT FROM AUTHOR]

We report an efficient synthesis of copper indium sulfide nanocrystals with strong photoluminescence in the visible to near-infrared. This method can produce gram quantities of material with a chemical yield in excess of 90% with minimal solvent waste. The overgrowth of as-prepared nanocrystals with a few monolayers of CdS or ZnS increases the photoluminescence quantum efficiency to> 80%. On the basis of time-resolved spectroscopic studies of core/shell particles, we conclude that the emission is due to an optical transition that couples a quantized electron state to a localized hole state, which is most likely associated with an internal defect. [ABSTRACT FROM AUTHOR]

My aim through this article is to propagate that Pinter has shown the neurotic anxiety, aloneness, identity and about envy in the play The Caretaker. In this play he has tried to show the inner Psyche of a character Davies. Harold Pinter lies in the exploration of the inner world of human psyche and sensibility. He explores the psychological recesses of an individual's quest for life itself, trying, thus to draw the meaning and reason behind the thinking prototype of an individual. He has perfectly treated the complex tracts of human psyche in his play The Caretaker. This play is an instruction in the psyche of people who lose their ability for rational consideration on being subjected to traumatic experiences. The Caretaker is one of Mr. Pinter's most satisfying psychological plays, with the careful combustion of its language and moments of almost deranged humor. [ABSTRACT FROM AUTHOR]

We describe optical switching in solutions of semiconductor nanocrystals illuminated by a 404 nm continuous wave laser source, driven by the formation of a micro-bubble of solvent vapor in the solution. Low boiling solvents such as hexane show an oscillatory modulation of transmitted light intensity (period ∼4 s) while solvents with intermediate boiling points such as toluene give a stable switching response. An on/off ratio of 83% is observed in the transmitted pump beam. Using this, a pump beam (404 nm, 80 mW continuous wave) was shown to reversibly switch the state of a probe laser (630 nm, 5 mW continuous wave). This switch thus serves as an optical analog of an electronic transistor and demonstrates the potential for all optical switching of low power light beams. Further, all optical universal logic gates, NAND and NOR, were also demonstrated using the micro-bubble switch.

We observe and study the anomalous Stokes shift of CuAlS 2 /CdS quantum dots. While all known I-III-VI 2 semiconductor core/shell quantum dots show Stokes shifts in excess of 100 meV, the shift associated with CuAlS 2 /CdS quantum dots is uniquely large, even exceeding 1.4 eV in some cases. CuAlS 2 /CdS quantum dots are thus associated with cross sections less than 10 -17 cm 2 under the emission maximum. We investigate this anomaly using spectroscopic techniques and ascribe it to the existence of a strong type-II offset between CuAlS 2 and CdS layers. Besides their strong Stokes shift, CuAlS 2 /CdS quantum dots also exhibit high quantum yields (63%) as well as long emission lifetimes (∼1500 ns). Because of the combined existence of these properties, CuAlS 2 /CdS quantum dots can act as tunable, transparent emitters over the entire visible spectrum. As a demonstration of their potential, we describe the construction of a wide area transparent lighting device with waveguided optical excitation and a clear aperture of 7.5 cm 2 .

While several potential applications of CuFeS 2 quantum dots have already been reported, doubts regarding their optical and physical properties persist. In particular, it is unclear if the quantum dot material is metallic, a degenerately doped semiconductor, or else an intrinsic semiconductor material. Here we examine the physical properties of CuFeS 2 quantum dots in order to address this issue. Specifically, we study the bump that is observed in the optical spectra of these quantum dots at ∼500 nm. Using a combination of structural and optical characterization methods, ultrafast spectroscopy, as well as electronic structure calculations, we ascertain that the unusual purple color of CuFeS 2 quantum dots as well the golden luster of CuFeS 2 films arise from the existence of a plasmon resonance in these materials. While the presence of free carriers causes this material to resemble gold, surface treatments are also described to suppress the plasmon resonance altogether.

Dielectric constants of MAPbX 3 (X = Br, I) in the 1 kHz-1 MHz range show strong temperature dependence near room temperature, in contrast to the nearly temperature-independent dielectric constant of CsPbBr 3 . This strong temperature dependence for MAPbX 3 in the tetragonal phase is attributed to the MA + dipoles rotating freely within the probing time scale. This interpretation is supported by ab initio molecular dynamics simulations on MAPbI 3 that establish these dipoles as randomly oriented with a rotational relaxation time scale of ∼7 ps at 300 K. Further, we probe the intriguing possibility of transient polarization of these dipoles following a photoexcitation process with important consequences on the photovoltaic efficiency, using a photoexcitation pump and second harmonic generation efficiency as a probe with delay times spanning 100 fs-1.8 ns. The absence of a second harmonic signal at any delay time rules out the possibility of any transient ferroelectric state under photoexcitation.

QM/MM calculations were performed on ethyl chlorophyllide-a and its radical cation and anion, by using the density functional (DF) B3LYP method to determine the molecular characteristics, and a molecular mechanics (MM) method to simulate the solvating medium. The presence of the solvent was accounted for during the optimization of the geometry of the 85-atom chlorophyll-a system by using an ONIOM methodology. A total of 24 solvent molecules were explicitly considered during the optimization process, and these were treated by the universal force field (UFF) method. Initially, the split-valence 3-21G basis set was used for optimizing the geometry of the 85-atom species, neutral, cation and anion. Electronic energies were then determined for the optimized species by making use of the polarized 6-31G(d) basis set. The ionization energy calculated (6.0 eV) is in very good agreement with the observed one (6.1 eV). The MM+ force field was used to investigate the dynamics of the acetonitrile molecules around the neutral species as well as the radical ions of chlorophyll. The required atomic charges on all the atoms were obtained from calculations on all involved molecules at the DFT/6-31G(d) level. Randomly sampled configurations were used to determine the first solvation layer contribution to the free energy of solvation of various species. A truncated 46-atom model of ethyl chlorophyllide-a was used to evaluate the thermal energies of neutral chlorophyll molecule relative to its two radical ions in the gas phase. Born energy, Onsager energy, and the Debye-Huckel energy of the chlorophyll-solvent aggregate were added as perturbative corrections to the free energy of solvation that was initially obtained through molecular dynamics method for the same complex. These calculations yield the oxidation potential as 0.75 +/- 0.32 V and the reduction potential -1.18 +/- 0.31 V at 298.15 K. The calculated values are in good agreement with the experimental midpoint potentials of +0.76 and -1.04 V, respectively.