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Vibronically Coupled Near-Infrared Emission and Excitation from <i>d</i>−<i>d</i> Transitions of Cs<sub>2</sub>MX<sub>6</sub> (M = Mo/W, X = Cl/Br)
No full textIn near-infrared (NIR)-emitting phosphors, the emission typically originates from forbidden d−d or f−f electronic transitions of metal ion dopants. But the excitation happens through higher-energy (UV or blue) allowed transitions, resulting in energy loss for this UV- or blue-to-NIR conversion. Here we report Cs2MX6 (M = Mo/W, X = Cl/Br) 0D perovskite derivatives with NIR excitation and emission arising from the same pair of d-electronic states, showing small Stokes shifts. The samples show significant optical absorption at 787 nm (12700 cm-1) and emission at 986 nm (10140 cm-1) because of the d2 electronic configuration of M4+ in isolated [MX6]2- octahedra. Interestingly, isolated [MX6]2- also leads to vibrational fine structures in the electronic excitation and emission spectra at cryogenic temperatures, which are rare for undoped inorganic crystals. Finally, phosphor-converted light-emitting diodes are fabricated by coating Cs2MoCl6 on commercial 730 nm LED chips without requiring UV-blue chips
Effect of film morphology on circular dichroism of low-dimensional chiral hybrid perovskites
No full textChiral hybrid lead halide perovskites show interesting chiral optoelectronic properties. The extent of chirality is often estimated by their circular dichroism (CD) response. Here, we show that the CD data depend strongly on film morphology. Four of the six chiral hybrid lead halide films prepared, 2D (R- and S-MBA)2PbI4 and 1D (R- and S-MBA)PbI3 (MBA: methylbenzylammonium), form homogenous non-textured films and show an isotropic CD signal. In contrast, the other two samples, 1D (R- and S-MBA)PbBr3, form textured films, showing uncorrelated CD signals from different parts of the film. Therefore, the role of film morphology needs to be verified before designing and comparing the chiroptic and chiral optoelectronic properties of hybrid perovskites
Unveiling Temperature-Induced Structural Phase Transition and Luminescence in Mn<sup>2+</sup>-Doped Cs<sub>2</sub>NaBiCl<sub>6</sub> Double Perovskite
No full textHalide double perovskites like Cs2NaBiCl6 are good host materials for luminescent dopants like Mn2+. The nature of photoluminescence (PL) depends on the local structure around the dopant ion, and doping may sometimes influence the global structure of the host. Here, we unveil the correlation between the temperature-induced (global) structural phase transition of Mn2+-doped Cs2NaBiCl6 with the local structure and PL of the Mn2+ dopant. X-ray diffraction analysis shows Mn2+-doped Cs2NaBiCl6 is in a cubic (Fm3m) phase between 300 and 110 K, below which the phase changes to tetragonal (I4/mmm), which persists at least until 15 K. The small (∼1%) doping amount does not alter the phase transition behavior of Cs2NaBiCl6. Importantly, the phase transition does not influence the Mn2+ d-electron PL. The PL peak energy, intensity, spectral width, and lifetime do not show any signature of the phase transition between 300–6 K. The hyperfine splitting in temperature-dependent electron paramagnetic spectra of Mn2+ ions also remain unchanged across the phase transition. These results suggest that the global structural phase transition of the host does not influence the local structure and emission property of the dopant Mn2+ ion. This structure–property insight might be explored for other transition-metal- and lanthanide-doped halide double perovskites as well. The stability of dopant emission regardless of the structural phase transition bodes well for their potential applications in phosphor-converted light emitting diodes
Assessment of climate variability and trends in different physiographic zones of North Western Himalayas
No full textHimalaya – one of the pristine and ecologically fragile mountain ecosystem is highly vulnerable to any small changes in climatic system. Under changing climate conditions, assessing regional trends become more important owing to dependence of more than 1 billion people on Himalayas. To analyze the climatic trends and magnitude, this study utilized the long term meteorological data (1980–2022) for temperature and precipitation. Investigations were carried out for 11 meteorological stations located in different topographical zones of Jammu, Kashmir and Ladakh region. The non-parametric Mann–Kendall test was used for significance of trends in precipitation and temperature data on monthly, seasonal, and annual scales, while Sen’s non-parametric estimator of the slope was used to estimate the magnitude of trend. For TMax, except Jammu plains (-0.018°C a-1) all regions experienced increasing trend with annual rate of increase 0.018°C a-1, 0.032oC a-1 and 0.051°C a-1 in Pir Panjal region, Kashmir valley and Ladakh region respectively. For annual TMin, all four geographical regions and individual stations have observed an increase. Ladakh region observed highest rate of increase (0.070°C a-1) which was significant followed by Pir Panjal region (0.048°C a-1), Kashmir valley (0.013°C a-1) and the lowest rate was observed in Jammu Plains (0.006°C a-1). Precipitation revealed a general decreasing trend with large inter annual variability. Seasonally, TMin has seen most significant changes across all topographical regions. Our results indicate that influence of Indian Summer Monsoon (ISM) was more towards the Jammu plains and its impact reduced towards Pir Panjal and Kashmir valley with increasing influence of Western Disturbances (WDs). Jammu plains received 75.8# precipitation from ISM while Kashmir valley received 72.4# precipitation from WDs. Shift in climatic variables could have serious environmental and socio-economic implications which can alter the regional ecological stability
Effects of Solar Variability on Tropical Cyclone Activity
No full textThe current study explores the relationship between solar variability and tropical cyclone (TC) activity using sunspot number (SSN) and TC best-track data as respective proxies. We have considered six regions of the globe, for example, EP: Eastern Pacific, NA: North Atlantic, NI: North Indian, SI: South Indian, SP: South Pacific, and WP: Western Pacific. The results show strong anti-correlation between yearly TC activity and yearly SSN while considering their 11-year moving averages. This behavior is consistent for TC counts as well as accumulated cyclone energy. However, this is true only for the North Atlantic region. Overall, when we consider all regions together, more TCs (in terms of counts) are observed during lower solar activity periods (SSN < 50) as compared to higher solar activity conditions (SSN > 100). However, the yearly rates remain more or less similar. On the other hand, extreme TC events with a maximum wind speed of 137 knots and higher (category 5) are most likely to occur during the declining phase of a solar cycle and least likely to occur during the ascending phase or the maximum phase. Although solar activity levels are similar during the declining and ascending phases, the yearly occurrence rate is nearly double in the declining phase (1.123) as compared to that in the ascending phase (0.625)
A brief on intertwined physico-chemical interactions of air pollutants during COVID-19 lockdown
No full textThis brief presents an intriguing aspect of the physico-chemical interactions among particulate matters (PM2.5; PM10) and several gases pollutants during pre- (01 March to 24 March 2020) and COVID-19 first phase of lockdown period (25 March to 30 April 2020) over Delhi-National Capital Region. In order to see the impact of lockdown on ambient particulate and gaseous pollutants, we have also compared the results of 2020 with a normal year 2019 and 2021. Results show relatively clean atmosphere (reduced pollutants concentrations except ozone) during lockdown period as compared to pre-lockdown period of 2020. Similar kinds of results are seen for comparison of 2019 and 2020 for lockdown period. Further, we explore the mechanisms enhancing ozone pollution over Delhi during the COVID-19 lockdown period, in contrast with trends in the fine particulate matter (PM2.5) and precursors of ozone (CO, NOx). We suggest that lower NOx has weakened the O3 chemical sink during the lockdown. Additionally, reduced aerosol loading allowed more incoming solar radiation favouring ozone production as seen by comparing with 2019 and 2021. The results may be important for policy makers to curb pollution in mega cities like Delhi
Deep Ensembling with Multimodal Image Fusion for Efficient Classification of Lung Cancer
No full textThis study focuses on the classification of cancerous and healthy slices from multimodal lung images. The data used in the research comprises Computed Tomography (CT) and Positron Emission Tomography (PET) images. The proposed strategy achieves the fusion of PET and CT images by utilizing Principal Component Analysis (PCA) and an Autoencoder. Subsequently, a new ensemble-based classifier developed, Deep Ensembled Multimodal Fusion (DEMF), employing majority voting to classify the sample images under examination. Gradient-weighted Class Activation Mapping (Grad-CAM) employed to visualize the classification accuracy of cancer-affected images. Given the limited sample size, a random image augmentation strategy employed during the training phase. The DEMF network helps mitigate the challenges of scarce data in computer-aided medical image analysis. The proposed network compared with state-of-the-art networks across three publicly available datasets. The network outperforms others based on the metrics - Accuracy, F1Score, Precision, and Recall. The investigation results highlight the effectiveness of the proposed network
The quantum mechanical non-adiabatic coupling term as friction in the formation of DH<sub>2</sub><sup>+</sup>
No full textBy going beyond the Born-Oppenheimer approximation and treating the non-adiabatic coupling terms (NACTs) as equivalent to a frictional force in a molecular system, the classical equations of motion are solved for a test case of (DH2)+. Using an ab initio potential energy surface for the ground electronic state and its NACTs with the first excited state of (DH2)+, it is shown that (D+, H2) collisions are slowed enough to result in trapping and formation of a stable DH2+
Autotrophy to Heterotrophy: Shift in Bacterial Functions During the Melt Season in Antarctic Cryoconite Holes
No full textMicrobes residing in cryoconite holes (debris, water, and nutrient-rich ecosystems) on the glacier surface actively participate in carbon and nutrient cycling. Not much is known about how these communities and their functions change during the summer melt-season when intense ablation and runoff alter the influx and outflux of nutrients and microbes. Here, we use high-throughput-amplicon sequencing, predictive metabolic tools and Phenotype MicroArray techniques to track changes in bacterial communities and functions in cryoconite holes in a coastal Antarctic site and the surrounding fjord, during the summer season. The bacterial diversity in cryoconite hole meltwater was predominantly composed of heterotrophs (Proteobacteria) throughout the season. The associated functional potentials were related to heterotrophic-assimilatory and -dissimilatory pathways. Autotrophic Cyanobacterial lineages dominated the debris community at the beginning and end of summer, while heterotrophic Bacteroidota- and Proteobacteria-related phyla increased during the peak melt period. Predictive functional analyses based on taxonomy show a shift from predominantly phototrophy-related functions to heterotrophic assimilatory pathways as the melt-season progressed. This shift from autotrophic to heterotrophic communities within cryoconite holes can affect carbon drawdown and nutrient liberation from the glacier surface during the summer. In addition, the flushing out and export of cryoconite hole communities to the fjord could influence the biogeochemical dynamics of the fjord ecosystem
An extreme precipitation event over Dronning Maud Land, East Antarctica - A case study of an atmospheric river event using the Polar WRF Model
No full textExtreme precipitation events (EPEs) are crucial in Antarctica, impacting the Antarctic ice sheet's surface mass balance and stability. Comprehensive case studies are essential for better understanding these events and the underlying processes driving them. Here, we investigate an extreme snowfall event in Dronning Maud Land (DML), East Antarctica on November 8 and 9, 2015. This event contributed approximately 22 % of the annual accumulation in less than two days and exhibited high spatial variability in precipitation distribution. We employed a high-resolution atmospheric model specifically optimized for the polar regions (Polar WRF) and ERA5 reanalysis data to analyze the event in detail. Our findings highlight the importance of a blocking high-pressure ridge of record strength that effectively blocked and diverted a strong extratropical cyclone into DML, ultimately leading to the heavy snowfall event. The sudden deepening of the cyclone was initiated by a 'jet streak' in the upper atmosphere that steered the system southeastwards towards the Antarctic coast. Notably, we observed an anomalously high poleward moisture transport in the form of a strong atmospheric river on November 7, 2015. This atmospheric river originated in the South Atlantic Ocean and tracked poleward from the 30°S-40°S latitude band. Vertical cross-sections of the model outputs indicate that most of the precipitation was concentrated in regions with steep orography along the path of the atmospheric river. This interaction between the atmospheric river and the steep terrain led to the uplift of maritime air, resulting in heavy snowfall. This study highlights the significance of extreme upper and lower atmospheric conditions in driving intense moisture transport towards coastal DML. The interaction between the atmospheric river and the steep orography contributed to heavy snowfall, underscoring the importance of considering orographic influences in understanding EPEs in Antarctica