Ultra-narrow and widely tunable Mn^(2+) Emission from Single Nanocrystals of ZnS-CdS alloy

Extensively studied Mn-doped semiconductor nanocrystals have invariably exhibited photoluminescence (PL) over a narrow energy window of width <= 149 meV in the orange-red region and a surprisingly large spectral width (>= 180 meV), contrary to its presumed atomic-like origin. Carrying out emission measurements on individual single nanocrystals and supported by ab initio calculations, we show that Mn PL emission, in fact, can (i) vary over a much wider range (~ 370 meV) covering the deep green-deep red region and (ii) exhibit widths substantially lower (~ 60-75 meV) than reported so far, opening newer application possibilities and requiring a fundamental shift in our perception of the emission from Mn-doped semiconductor nanocrystals.Comment: 5 pages, 5 figure

Size-Dependent Lattice Structure and Confinement Properties in CsPbI₃ Perovskite Nanocrystals: Negative Surface Energy for Stabilization

CsPbI₃ nanocrystals with narrow size distributions were prepared to study the size-dependent properties. The nanocrystals adopt the perovskite (over the nonperovskite orthorhombic) structure with improved stability over thin-film materials. Among the perovskite phases (cubic α, tetragonal β, and orthorhombic γ), the samples are characterized by the γ phase, rather than α, but may have a size-dependent average tilting between adjacent octahedra. Size-dependent lattice constants systematically vary 3% across the size range, with unit cell volume increasing linearly with the inverse of size to 2.1% for the smallest size. We estimate the surface energy to be from −3.0 to −5.1 eV nm⁻² for ligated CsPbI₃ nanocrystals. Moreover, the size-dependent bandgap is best described using a nonparabolic intermediate confinement model. We experimentally determine the bulk bandgap, effective mass, and exciton binding energy, concluding with variations from the bulk α-phase values. This provides a robust route to understanding γ-phase properties of CsPbI₃

Electric and magnetic polarizabilities of hexagonal Ln2CuTiO6 (Ln=Y, Dy, Ho, Er and Yb)

We investigated the rare-earth transition metal oxide series, Ln2CuTiO6 (Ln=Y, Dy, Ho, Er and Yb), crystallizing in the hexagonal structure with non-centrosymmetric P63cm space group for possible occurrences of multiferroic properties. Our results show that while these compounds, except Ln=Y, exhibit a low temperature antiferromagnetic transition due to the ordering of the rare-earth moments, the expected ferroelectric transition is frustrated by the large size difference between Cu and Ti at the B-site. Interestingly, this leads these compounds to attain a rare and unique combination of desirable paraelectric properties with high dielectric constants, low losses and weak temperature and frequency dependencies. First-principles calculations establish these exceptional properties result from a combination of two effects. A significant difference in the MO5 polyhedral sizes for M = Cu and M = Ti suppress the expected co-operative tilt pattern of these polyhedra, required for the ferroelectric transition, leading to relatively large values of the dielectric constant for every compound investigated in this series. Additionally, it is shown that the majority contribution to the dielectric constant arises from intermediate-frequency polar vibrational modes, making it relatively stable against any temperature variation. Changes in the temperature stability of the dielectric constant amongst different members of this series are shown to arise from changes in relative contributions from soft polar modes.Comment: Accepted for publication in Phys. Rev. B (21 pages, 2 Table, 8 Figures

Enhanced Open-Circuit Voltage of Wide-Bandgap Perovskite Photovoltaics by Using Alloyed (FA1–xCsx)Pb(I1–xBrx)3 Quantum Dots

We report a detailed study on APbX3 (A=Formamidinium (FA+), Cs+; X=I-, Br-) perovskite quantum dots (PQDs) with combined A- and X-site alloying that exhibit, both, a wide bandgap and high open circuit voltage (Voc) for the application of a potential top cell in tandem junction photovoltaic (PV) devices. The nanocrystal alloying affords control over the optical bandgap and is readily achieved by solution-phase cation and anion exchange between previously synthesized FAPbI3 and CsPbBr3 PQDs. Increasing only the Br- content of the PQDs widens the bandgap but results in shorter carrier lifetimes and associated Voc losses in devices. These deleterious effects can be mitigated by replacing Cs+ with FA+, resulting in wide bandgap PQD absorbers with improved charge-carrier mobility and PVs with higher Voc. Although further device optimization is required, these results demonstrate the potential of FA1–xCsx)Pb(I1–xBrx)3 PQDs for wide bandgap perovskite PVs with high Voc

CsI‐Antisolvent Adduct Formation in All‐Inorganic Metal Halide Perovskites

The excellent optoelectronic properties demonstrated by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, high‐performance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the lead‐halide precursor salts. These adduct‐based precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in all‐inorganic perovskites such as CsPbI3. In this work, inorganic perovskite composition CsPbI3 is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other A‐site cation salts. These CsI adducts control nucleation more so than the PbI2–dimethyl sulfoxide (DMSO) adduct and demonstrate how the A‐site plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsI–MeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.It is found that unique adducts form between CsI and dimethyl sulfoxide (DMSO) and certain antisolvents, such as methyl acetate, during film formation of the all‐inorganic perovskite CsPbI3. These adducts significantly influence crystallization and the power conversion efficiency of the resulting solar cells.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/1/aenm201903365-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/2/aenm201903365.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/3/aenm201903365_am.pd

CsI‐Antisolvent Adduct Formation in All‐Inorganic Metal Halide Perovskites

The excellent optoelectronic properties demonstrated by hybrid organic/inorganic metal halide perovskites are all predicated on precisely controlling the exact nucleation and crystallization dynamics that occur during film formation. In general, high‐performance thin films are obtained by a method commonly called solvent engineering (or antisolvent quench) processing. The solvent engineering method removes excess solvent, but importantly leaves behind solvent that forms chemical adducts with the lead‐halide precursor salts. These adduct‐based precursor phases control nucleation and the growth of the polycrystalline domains. There has not yet been a comprehensive study comparing the various antisolvents used in different perovskite compositions containing cesium. In addition, there have been no reports of solvent engineering for high efficiency in all‐inorganic perovskites such as CsPbI3. In this work, inorganic perovskite composition CsPbI3 is specifically targeted and unique adducts formed between CsI and precursor solvents and antisolvents are found that have not been observed for other A‐site cation salts. These CsI adducts control nucleation more so than the PbI2–dimethyl sulfoxide (DMSO) adduct and demonstrate how the A‐site plays a significant role in crystallization. The use of methyl acetate (MeOAc) in this solvent engineering approach dictates crystallization through the formation of a CsI–MeOAc adduct and results in solar cells with a power conversion efficiency of 14.4%.It is found that unique adducts form between CsI and dimethyl sulfoxide (DMSO) and certain antisolvents, such as methyl acetate, during film formation of the all‐inorganic perovskite CsPbI3. These adducts significantly influence crystallization and the power conversion efficiency of the resulting solar cells.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/1/aenm201903365-sup-0001-SuppMat.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/2/aenm201903365.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154525/3/aenm201903365_am.pd

Оценивание финансово-экономической безопасности предприятий молокоперерабатывающей отрасли

The essence of the concept “financial and economic security of the enterprise” is covered. Methodological approaches to the enterprise financial and economic security evaluation are considered, enabling the method of index numberrating score of the enterprise financial and economic security to be found. Dynamics of milk anddairy production in Ukraine has been studied. Ukrainian regions leading in liquid processed milk production have been identified. Dynamics of milk and dairy production per man has been analyzed which allowed to find out the annual increase in demand per man. Integrated index of the dairy enterprise financial and economic security has been evaluated. As a result, the ways to increase the managerial efficiency of financial and economic security of the following enterprises:PJSC "Dubnomoloko", PJSC "Kupyans'ki milk canning plant", PJSC the "Yagotyns'ki creamery", PJSC the "Pervomais'ki milk canning plant" are offered.У статті розкрито сутність поняття фінансово-економічної безпеки підприємства. Розглянуто методичні підходи щодо оцінювання фінансово-економічної безпеки підприємства, що дозволило виявити підхід рейтингової оцінки показника фінансово-економічної безпеки підприємства. Досліджено динаміку виробництва молока та молочних продуктів України. Виявити області України, які є лідерами з виробництва молока рідкого обробленого. Проаналізовано динаміку виробництва молока та молочних продуктів на одну особу, що дозволило встановити щорічне зростання попиту на одну особу. Визначено підприємства молокопереробної галузі. Проведено оцінку інтегрального показника фінансово-економічної безпеки підприємств молокопереробної галузі. За результатами оцінки запропоновано шляхи підвищення ефективності управління фінансово-економічної безпеки таких підприємств, як: ПАТ «Дубномолоко», ПАТ «Куп’янський молочноконсервний комбінат», ПАТ «Яготинський маслозавод», ПАТ «Первомайський молочноконсервний комбінат».В статье раскрыто сущность понятия финансово-экономическая безопасность предприятия. Рассмотрено методические подходы относительно оценивания финансово-экономической безопасности предприятия, что позволило выявить поход рейтинговой оценки показателя финансово-экономической безопасности предприятия. Исследовано динамику производства молока и молочных продуктов Украины. Выявлены области Украины, которые являются лидерами по производству молока жидкого обработанного. Проанализировано динамику производства молока и молочных продуктов на одного человека, что позволило установить ежегодный рост спроса на одного человека. Определены предприятия молокоперерабатывающей отрасли. Проведена оценка интегрального показателя финансово-экономической безопасности предприятий молокоперерабатывающей отрасли. По результатам оценки предложены пути повышения эффективности управления финансово-экономической безопасности таких предприятий, как: ПАО «Дубномолоко», ПАО «Купянский молочноконсервный комбинат», ПАО «Яготинский маслозавод», ПАО «Первомайский молочноконсервный комбинат»

Rainbow Emission from an Atomic Transition in Doped Quantum Dots

Although semiconductor quantum dots are promising materials for displays and lighting due to their tunable emissions, these materials also suffer from the serious disadvantage of self-absorption of emitted light. The reabsorption of emitted light is a serious loss mechanism in practical situations because most phosphors exhibit subunity quantum yields. Manganese-based phosphors that also exhibit high stability and quantum efficiency do not suffer from this problem but in turn lack emission tunability, seriously affecting their practical utility. Here, we present a class of manganese-doped quantum dot materials, where strain is used to tune the wavelength of the dopant emission, extending the otherwise limited emission tunability over the yellow-orange range for manganese ions to almost the entire visible spectrum covering all colors from blue to red. These new materials thus combine the advantages of both quantum dots and conventional doped phosphors, thereby opening new possibilities for a wide range of applications in the future