The Stokes Shift and Exciton Fine Structure in Strongly Confined CsPbBr3 Perovskite Nanoplatelets.

The Stokes shift is negligible in bulk perovskites but large in two-dimensional (2D) CsPbBr3 perovskites. The issue has attracted a lot of discussion, but it remains controversial. Here, we report the temperature-dependent absorption and photoluminescence (PL) spectra of CsPbBr3 perovskite nanoplatelets (NPLs). We observe a temperature-dependent Stokes shift changing from 26 to 41 meV. This phenomenon was attributed to the exciton fine structure according to the great difference in peak width. The triple bright exciton levels all participate in the absorption process and result in a wide absorption peak, while only the lowest exciton level contributes to photon emission and exhibits a relatively narrow PL peak. The PL decay curves also present the characterization of bright and dark exciton couplings at low temperatures. The splitting of triple bright excitons is induced by the morphology anisotropy of the 2D structure, so the large Stokes shift is proposed to be an intrinsic property of 2D perovskites.

The Rashba effect in two-dimensional hybrid perovskites: the impacts of halogens and surface ligands.

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) have gained much research interest nowadays due to their outstanding optoelectronic properties; however, the properties of the Rashba effect in 2D HOIPs have not been fully interpreted. In this work, a detailed thickness dependent structural distortion along with the Rashba splitting energy were investigated. Three types of HOIPs, 2D MAPbCl3, 2D MAPbBr3 and 2D MAPbI3, were adopted to compare the effect of halogens; and three surface ligands, BA, tert-BA and PEA, were adopted to explore the effect of ligands. It turns out that the structural distortion degree decreases with oscillations as the thickness increases, the Rashba splitting magnitude follows the same tendency, and 2D MAPbI3 is less sensitive to the thickness change compared to 2D MAPbBr3 or 2D MAPbCl3. Furthermore, different ligands and their orientations could have dramatically different impacts on the Rashba splitting. The PEA ligands enhance the Rashba splitting magnitude while the BA ligands have the reverse effect, and the impact of tert-BA ligands is insensitive to the increasing thickness. The partial charge density analysis shows that the band edges could be contributed by a charge density at a specific layer in the structure; thus, the Rashba effect is layer dependent in 2D HOIPs. These results provide some new perspectives on the Rashba effect in 2D HOIPs.

Differential effects of acute versus chronic dietary fructose consumption on metabolic responses in FVB/N mice.

Increased human consumption of high-fructose corn syrup has been linked to the marked increase in obesity and metabolic syndrome. Previous studies on the rapid effects of a high-fructose diet in mice have largely been confined to the C57BL/6 strains. In the current study, the FVB/N strain of mice that are resistant to diet-induced weight gain were used and fed a control or high-fructose diet for 48 h or for 12 wk. Many of the previously reported changes that occurred upon high-fructose feeding for 48 h in C57BL/6 mice were recapitulated in the FVB/N mice. However, the acute increases in fructolytic and lipogenic gene expression were completely lost during the 12-wk dietary intervention protocol. Furthermore, there was no significant weight gain in FVB/N mice fed a high-fructose diet for 12 wk, despite an overall increase in caloric consumption and an increase in average epididymal adipocyte cell size. These findings may be in part explained by a commensurate increase in energy expenditure and in carbohydrate utilization in high-fructose-fed animals. Overall, these findings demonstrate that FVB/N mice are a suitable model for the study of the effects of dietary intervention on metabolic and molecular parameters. Furthermore, the rapid changes in hepatic gene expression that have been widely reported were not sustained over a longer time course. Compensatory changes in energy expenditure and utilization may be in part responsible for the differences obtained between acute and chronic high-fructose feeding protocols.

Conformal Microfluidic-Blow-Spun 3D Photothermal Catalytic Spherical Evaporator for Omnidirectional Enhanced Solar Steam Generation and CO2 Reduction.

Solar-driven water evaporation and valuable fuel generation is an environmentally friendly and sustainable way for clean water and energy production. However, a few bottlenecks for practical applications are high-cost, low productivity, and severe sunlight angle dependence. Herein, solar evaporation with enhanced photocatalytic capacity that is light direction insensitive and of efficiency breakthrough by virtue of a three-dimensional (3D) photothermal catalytic spherical isotopic evaporator is demonstrated. A homogeneous layer of microfluidic blow spun polyamide nanofibers loaded with efficient light absorber of polypyrrole nanoparticles conformally wraps onto a lightweight, thermal insulating plastic sphere, featuring favorable interfacial solar heating and efficient water transportation. The 3D spherical geometry not only guarantees the omnidirectional solar absorbance by the light-facing hemisphere, but also keeps the other hemisphere under shadow to harvest energy from the warmer environment. As a result, the light-to-vapor efficiency exceeds the theoretical limit, reaching 217% and 156% under 1 and 2 sun, respectively. Simultaneously, CO2 photoreduction with generated steam reveals a favorable clean fuels production rate using photocatalytic spherical evaporator by secondary growth of Cu2 O nanoparticles. Finally, an outdoor demonstration manifests a high evaporation rate and easy-to-perform construction on-site, providing a promising opportunity for efficient and decentralized water and clean fuel production.

Two-Dimensional Planar BGe Monolayer as an Anode Material for Sodium-Ion Batteries.

Using first-principles swarm intelligence structure prediction computations, we explore a fully planar BGe monolayer with unique mechanical and electrical properties. Theoretical calculations reveal that a free-standing BGe monolayer has excellent stability, which is confirmed by the cohesive energy (compared to experimentally synthetic borophene and germanene monolayers), phonon modes (no imaginary frequencies appeared in the phonon spectrum), ab initio molecular dynamics (AIMD) simulations (no broken bonds and geometric reconstructions), and mechanical stability criteria. The metallic feature of the BGe monolayer can be maintained after absorbing different numbers of Na atoms, ensuring good electronic conductivity during the charge/discharge process. The calculated migration energy barrier, open-circuit voltage, and theoretical specific capacity of the BGe monolayer are much better than those of some other two-dimensional (2D) materials. These findings render the BGe monolayer a potential candidate for reversible Na-ion battery anode materials with desirable performance.

In celebration of a century with insulin - Update of insulin gene mutations in diabetes.

BACKGROUND: While insulin has been central to the pathophysiology and treatment of patients with diabetes for the last 100 years, it has only been since 2007 that genetic variation in the INS gene has been recognised as a major cause of monogenic diabetes. Both dominant and recessive mutations in the INS gene are now recognised as important causes of neonatal diabetes and offer important insights into both the structure and function of insulin. It is also recognised that in rare cases, mutations in the INS gene can be found in patients with diabetes diagnosed outside the first year of life. SCOPE OF REVIEW: This review examines the genetics and clinical features of monogenic diabetes resulting from INS gene mutations from the first description in 2007 and includes information from 389 patients from 292 families diagnosed in Exeter with INS gene mutations. We discuss the implications for diagnosing and treating this subtype of monogenic diabetes. MAJOR CONCLUSIONS: The dominant mutations in the INS gene typically affect the secondary structure of the insulin protein, usually by disrupting the 3 disulfide bonds in mature insulin. The resulting misfolded protein results in ER stress and beta-cell destruction. In contrast, recessive INS gene mutations typically result in no functional protein being produced due to reduced insulin biosynthesis or loss-of-function mutations in the insulin protein. There are clinical differences between the two genetic aetiologies, between the specific mutations, and within patients with identical mutations.

Free and self-trapped exciton emission in perovskite CsPbBr3 microcrystals.

The all-inorganic perovskite CsPbBr3 has been capturing extensive attention due to its high quantum yield in luminescence devices and relatively high stability. Its luminescence is dominated by free exciton (FE) recombination but additional emission peaks were also commonly observed. In this work, a CsPbBr3 microcrystal sample in the orthorhombic phase was prepared by the chemical vapor deposition method. In addition to the FE peak, a broad emission peak was found in this sample and it was attributed to self-trapped excitons (STEs) based on its photophysical properties. The STE emission can only be observed below 70 K. The derived Huang-Rhys factor is ∼12 and the corresponding phonon energy is 15.3 meV. Its lifetime is 123 ns at 10 K, much longer than that of FE emission. The STE emission is thought to be an intrinsic property of CsPbBr3.

Two-dimensional Ga2O2 monolayer with tunable band gap and high hole mobility.

By means of density functional theory and unbiased structure search computations, we systematically investigated the stability and electronic properties of a new Ga2O2 monolayer. The phonon spectra and ab initio molecular dynamics simulations show that the Ga2O2 monolayer is dynamically and thermally stable. Moreover, it also shows superior open-air stability. In particular, the Ga2O2 monolayer is an indirect semiconductor with a wide band gap of 2.752 eV and high hole mobility of 4720 cm2 V-1 s-1. Its band gap can be tuned flexibly in a large range by applied strain and layer control. It exhibits high absorption coefficients (>105 cm-1) in the ultraviolet region. The combined novel electronic properties of the Ga2O2 monolayer imply that it is a highly promising material for future applications in electronics and optoelectronics.

Steady-state and time-resolved upconversion photoluminescence in Yb3+-Er3+ co-doped transparent ceramics of YAG.

Transparent ceramics (TCs) represent a new family of functional hard materials. In this Letter, steady-state and time-resolved upconversion photoluminescence in Yb3+-Er3+ co-doped TC of yttrium aluminum garnet (TC-YAG) are reported for the first time, to the best of our knowledge. Under the excitation of near-infrared 940 nm laser at room temperature, the Yb3+-Er3+ co-doped TC-YAG emits intense multi-color luminescence consisting of cyan, green, and red groups of sharp lines. More excitingly, the green group of luminescence due to the transitions from 4S3/2 to 4I15/2 states of Er3+ are the prominent components with the average lifetime of ∼0.3ms. The internal quantum efficiency of the green luminescence is estimated to be 32.8%. A unique dual-resonance energy transfer from Yb3+ to Er3+ via the excited-state vibronic transitions is proposed as the principal mechanism of the strongest green luminescence of Er3+ ions in TC-YAG.

SMRT Regulates Metabolic Homeostasis and Adipose Tissue Macrophage Phenotypes in Tandem.

The Silencing Mediator of Retinoid and Thyroid Hormone Receptors (SMRT) is a nuclear corepressor, regulating the transcriptional activity of many transcription factors critical for metabolic processes. While the importance of the role of SMRT in the adipocyte has been well-established, our comprehensive understanding of its in vivo function in the context of homeostatic maintenance is limited due to contradictory phenotypes yielded by prior generalized knockout mouse models. Multiple such models agree that SMRT deficiency leads to increased adiposity, although the effects of SMRT loss on glucose tolerance and insulin sensitivity have been variable. We therefore generated an adipocyte-specific SMRT knockout (adSMRT-/-) mouse to more clearly define the metabolic contributions of SMRT. In doing so, we found that SMRT deletion in the adipocyte does not cause obesity-even when mice are challenged with a high-fat diet. This suggests that adiposity phenotypes of previously described models were due to effects of SMRT loss beyond the adipocyte. However, an adipocyte-specific SMRT deficiency still led to dramatic effects on systemic glucose tolerance and adipocyte insulin sensitivity, impairing both. This metabolically deleterious outcome was coupled with a surprising immune phenotype, wherein most genes differentially expressed in the adipose tissue of adSMRT-/- mice were upregulated in pro-inflammatory pathways. Flow cytometry and conditioned media experiments demonstrated that secreted factors from knockout adipose tissue strongly informed resident macrophages to develop a pro-inflammatory, MMe (metabolically activated) phenotype. Together, these studies suggest a novel role for SMRT as an integrator of metabolic and inflammatory signals to maintain physiological homeostasis.

Arsenic Exposure Decreases Adiposity During High-Fat Feeding.

OBJECTIVE: Arsenic is an endocrine-disrupting chemical associated with diabetes risk. Increased adiposity is a significant risk factor for diabetes and its comorbidities. Here, the impact of chronic arsenic exposure on adiposity and metabolic health was assessed in mice. METHODS: Male C57BL/6J mice were provided ad libitum access to a normal or high-fat diet and water +/- 50 mg/L of sodium arsenite. Changes in body weight, body composition, insulin sensitivity, energy expenditure, and locomotor activity were measured. Measures of adiposity were compared with accumulated arsenic in the liver. RESULTS: Despite uniform arsenic exposure, internal arsenic levels varied significantly among arsenic-exposed mice. Hepatic arsenic levels in exposed mice negatively correlated with overall weight gain, individual adipose depot masses, and hepatic triglyceride accumulation. No effects were observed in mice on a normal diet. For mice on a high-fat diet, arsenic exposure reduced fasting insulin levels, homeostatic model assessment of insulin resistance and ß-cell function, and systemic insulin resistance. Arsenic exposure did not alter energy expenditure or activity. CONCLUSIONS: Collectively, these data indicate that arsenic is antiobesogenic and that concentration at the source poorly predicts arsenic accumulation and phenotypic outcomes. In future studies, investigators should consider internal accumulation of arsenic rather than source concentration when assessing the outcomes of arsenic exposure.

Anomalous variable-temperature photoluminescence of CsPbBr3 perovskite quantum dots embedded into an organic solid.

All-inorganic lead halide perovskite quantum dots (PQDs) of CsPbBr3 were synthesized at room temperature via a facile solution-based procedure. The cubic phase structure of the synthesized PQDs was judiciously identified through examining high-resolution transmission electron microscopy (TEM) images, selected area electronic diffraction (SAED) patterns and scanning TEM images of the PQDs. Variable-temperature photoluminescence (PL) spectra of the CsPbBr3 PQDs randomly embedded into a frozen solid of methylbenzene were measured in the temperature range of 5-180 K. It is found that both the linewidth and peak position of the measured PL spectra are abnormally almost temperature independent in the temperature range of interest. Some competing mechanisms, such as a competition between the bandgap blue shift induced by thermal lattice expansion and red shift induced by thermal escaping of localized excitons, and a competition between lineshape broadening by phonon scattering and narrowing by thermal escaping of localized excitons, are proposed to interpret the phenomena. Good agreement between the theoretical fitting and the experimental data leads to a state-of-the-art understanding of the temperature-dependent luminescence of the CsPbBr3 PQDs in a solid matrix.

Mechanism of Single-Photon Upconversion Photoluminescence in All-Inorganic Perovskite Nanocrystals: The Role of Self-Trapped Excitons.

The efficient single-photon upconversion photoluminescence (UCPL) feature of lead halide perovskite semiconductors makes it promising for developing laser cooling devices. This is an attractive potential application, but the underlying physics still remains unclear so far. By using the all-inorganic CsPbX3 (X = Br, I) nanocrystal samples, this phenomenon was investigated by photoluminescence (PL) and time-resolved PL under different temperatures and various excitation conditions. A broad emission band located at the low-energy side of the free exciton (FE) peak was detected and deduced to be from the self-trapped exciton (STE). The lifetime of STE emission was found to be 171 ns at 10 K, much longer than that of FE. The UCPL phenomenon was then attributed to thermal activation of transformation from STEs to FEs, and the energy barrier was derived to be 103.7 meV for CsPbBr3 and 45.2 meV for CsPb(Br/I)3, respectively. The transformation also can be seen from the fluorescence decay processes.

METTL14 is essential for ß-cell survival and insulin secretion.

Defects in the development, maintenance or expansion of ß-cell mass can result in impaired glucose metabolism and diabetes. N6-methyladenosine affects mRNA stability and translation efficiency, and impacts cell differentiation and stress response. To determine if there is a role for m6A in ß-cells, we investigated the effect of Mettl14, a key component of the m6A methyltransferase complex, on ß-cell survival and function using rat insulin-2 promoter-Cre-mediated deletion of Mettl14 mouse line (ßKO). We found that ßKO mice with normal chow exhibited glucose intolerance, lower levels of glucose-stimulated insulin secretion, increased ß-cell death and decreased ß-cell mass. In addition, HFD-fed ßKO mice developed glucose intolerance, decreased ß-cell mass and proliferation, exhibited lower body weight, increased adipose tissue mass, and enhanced insulin sensitivity due to enhanced AKT signaling and decreased gluconeogenesis in the liver. HFD-fed ßKO mice also showed a decrease in de novo lipogenesis, and an increase in lipolysis in the liver. RNA sequencing in islets revealed that Mettl14 deficiency in ß-cells altered mRNA expression levels of some genes related to cell death and inflammation. Together, we showed that Mettl14 in ß-cells plays a key role in ß-cell survival, insulin secretion and glucose homeostasis.

A theoretical study of several fully hydrogenated borophenes.

Several recently synthesized two dimensional borophene monolayers are almost all metallic with a strong anisotropic character, but their structural instability and the need to explore their novel physical properties are still ongoing issues. We present a detailed study of four fully hydrogenated borophenes (ß12, δ3, δ5 and α borophanes) by first-principles calculations. According to phonon dispersion relations and ab initio molecular dynamics simulations, δ3 and δ5 borophanes are dynamically and thermally stable. The structural, mechanical, and electronic properties of δ3 and δ5 borophanes are analyzed. The results indicate that charge transfer from B to H atoms is crucial for the stability of two borophane phases. The HSE06 calculations predict that both δ3 and δ5 borophanes are semiconductors with indirect band gaps of 1.51 and 1.99 eV, respectively. These findings indicate that δ3 and δ5 borophanes are ideal for applications in nanoelectronics.

Luminescence and thermal behaviors of free and trapped excitons in cesium lead halide perovskite nanosheets.

Very recently, all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanostructures such as nanoparticles, nanoplates, and nanorods have been extensively explored. These CsPbX3 nanostructures exhibit excellent optical properties; however, the photophysics involved is not yet clear. Herein, the emission properties and luminescence mechanism of CsPbBr3 nanosheets (NSs) were investigated using steady-state and time-resolved photoluminescence (PL) spectroscopic techniques. Moreover, two kinds of excitonic emissions (Peak 1 and Peak 2) are observed at low temperatures (<80 K) under the conditions of low excitation level. They are revealed to stem from the radiative recombination of trapped and free excitons by examining their spectral features and emission intensity dependences on excitation power. Thermally induced exchange between the two kinds of excitons is found and modeled quantitatively; this has led to the determination of an activation energy of 13 meV. Thermal redistribution of trapped excitons and thermal expansion-induced blueshift of the bandgap are jointly responsible for the abnormal temperature dependence of the position of Peak 1, whereas the latter is predominant for the monotonic blueshift of the position of Peak 2 with an increase in temperature. These results and findings shed some light on the complicated luminescence mechanism of CsPbBr3 NSs.

Large Negative-Thermal-Quenching Effect in Phonon-Induced Light Emissions in Mn4+-Activated Fluoride Phosphor for Warm-White Light-Emitting Diodes.

Currently, hunting for anti-temperature-degradation high-efficiency phosphors has become crucially significant for fabricating high-brightness phosphor-converted white light-emitting diodes (pc-WLEDs). Herein, we show that photoluminescence in a kind of full-solution-processed K2SiF6:Mn4+ red phosphor exhibits an extraordinarily large negative thermal quenching property. For instance, under the excitation of 477 nm laser light, the sample photoluminescence intensity amazingly increases by 347-fold when the temperature is increased from 4 to 477 K. The temperature-driven transition probability enhancement of the phonon-induced luminescence around Mn4+ ions in the phosphor is argued to be responsible for the large negative-thermal-quenching phenomenon. We also demonstrate a pc-WLED with R a of 82 and correlated color temperature of 2701 K by using the K2SiF6:Mn4+ red phosphor + commercial yellow phosphor of YAG:Ce3+.

Observation of two-times self-focusing of femtosecond laser beam in ZnO crystal by two-photon luminescence.

By "seeing" the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the self-focusing effect makes a significant contribution to the formation of the first focusing point, while the second focusing point is caused by self-refocusing. The position of the first focusing point is in good agreement with the value predicted by a model developed by Chin and his co-workers. These experimental findings could be the unprecedented evidence for the self-focusing and refocusing effect of the femtosecond laser filament propagation in nonlinear media.

The Absence of Laminin α4 in Male Mice Results in Enhanced Energy Expenditure and Increased Beige Subcutaneous Adipose Tissue.

Laminin α4 (LAMA4) is located in the extracellular basement membrane that surrounds each individual adipocyte. Here we show that LAMA4 null (Lama4-/-) mice exhibit significantly higher energy expenditure (EE) relative to wild-type (WT) mice at room temperature and when exposed to a cold challenge, despite similar levels of food intake and locomotor activity. The Lama4-/- mice are resistant to age- and diet-induced obesity. Expression of uncoupling protein 1 is higher in subcutaneous white adipose tissue of Lama4-/- mice relative to WT animals on either a chow diet or a high-fat diet. In contrast, uncoupling protein 1 expression was not increased in brown adipose tissue. Lama4-/- mice exhibit significantly improved insulin sensitivity compared with WT mice, suggesting improved metabolic function. Overall, these data provide critical evidence for a role of the basement membrane in EE, weight gain, and systemic insulin sensitivity.

Arsenic exposure induces glucose intolerance and alters global energy metabolism.

Environmental pollutants acting as endocrine-disrupting chemicals (EDCs) are recognized as potential contributors to metabolic disease pathogenesis. One such pollutant, arsenic, contaminates the drinking water of ~100 million people globally and has been associated with insulin resistance and diabetes in epidemiological studies. Despite these observations, the precise metabolic derangements induced by arsenic remain incompletely characterized. In the present study, the impact of arsenic on in vivo metabolic physiology was examined in 8-wk-old male C57BL/6J mice exposed to 50 mg/l inorganic arsenite in their drinking water for 8 wk. Glucose metabolism was assessed via in vivo metabolic testing, and feeding behavior was analyzed using indirect calorimetry in metabolic cages. Pancreatic islet composition was assessed via immunofluorescence microscopy. Arsenic-exposed mice exhibited impaired glucose tolerance compared with controls; however, no difference in peripheral insulin resistance was noted between groups. Instead, early insulin release during glucose challenge was attenuated relative to the rise in glycemia. Despite decreased insulin secretion, pancreatic ß-cell mass was not altered, suggesting that arsenic primarily disrupts ß-cell function. Finally, metabolic cage analyses revealed that arsenic exposure induced novel alterations in the diurnal rhythm of food intake and energy metabolism. Taken together, these data suggest that arsenic exposure impairs glucose tolerance through functional impairments in insulin secretion from ß-cells rather than by augmenting peripheral insulin resistance. Further elucidation of the mechanisms underlying arsenic-induced behavioral and ß-cell-specific metabolic disruptions will inform future intervention strategies to address this ubiquitous environmental contaminant and novel diabetes risk factor.