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Tetragonal NaCe(WO4)2 with oxygen vacancy has been successfully synthesised by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal technique. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, etc. have been employed for detailed structural analysis, whilst oxygen vacancies, explored by Raman, FTIR and X-ray photoelectron spectroscopies, lead to distorted CeO8 dodecahedra (c.a. CeO7 and CeO6). It has been observed from photoluminescence spectra that the synthesised samples exhibit intense emission at 435 nm due to 5d–4f transition of Ce3+ within CeO8 dodecahedra, whilst emission at 485 nm is assigned for same transition within CeO7. CeO6 provides two emissions at 451 and 520 nm. Herein, we have identified that CTAB plays an important role in the formation of CeO7 and CeO6. In contrast to earlier ethylene-diamine–tetra-acetic acid-assisted NaCe(WO4)2 with predominant green emission, our samples exhibit strong violet emission indicating less formation of CeO7 and CeO6 by CTAB. Herein, our ab initio calculation using density functional theory reveals that valence and conduction bands comprise O 2p and O 2p–Ce 5d orbitals, respectively, whilst Ce 5dz2 and 5dyz, 5dxz orbitals mostly facilitate 5d–4f transition within CeO7 and CeO6. Commission Internationale de l'Elcairage coordinates are found in violet region with correlated colour temperature ~ 6491 K indicating that CTAB-assisted hydrothermally synthesised NaCe(WO4)2 can be a potential material for cold solid-state lighting application. [ABSTRACT FROM AUTHOR]

Triclinic NaCe(WO4)2 with oxygen monovacancies and divacancies has been successfully prepared via a facile cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal technique. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been employed to determine the unit cell and microstructure of the NaCe(WO4)2. The oxygen vacancies, structural distortion etc. have been investigated using Fourier-transform infrared, Raman and X-ray photoelectron spectroscopies. The synthesized samples exhibit an intense blue emission at 434 nm due to the 5d–4f transition of Ce3+ within the CeO8 dodecahedra, while the emission at 485 nm is ascribed to the 5d–4f transition within CeO7. It has also been identified that two emissions at 451 and 520 nm come from CeO6. Additionally, we find that the temperature of the hydrothermal reaction guides the formation of CeO7 and CeO6. In contrast to a previous ethylenediamine tetraacetic acid (EDTA)-assisted synthesis of NaCe(WO4)2 that results in a predominant green emission, our samples exhibit strong violet emissions indicating that less CeO7 and CeO6 is formed when using CTAB. We have also conducted ab initio calculations using density-functional theory, which reveals that the valence and conduction bands comprise of the O 2p orbitals and a O 2p–Ce 5d hybridization, respectively. The Ce 5dz2, 5dyz and 5dxz orbitals mostly facilitate the 5d–4f transition within the CeO7 and CeO6 polyhedra. Commission Internationale de I'Eclairage coordinates are found in the blue region with a correlated color temperature (CCT) of ∼7715 K indicating the potential for α-NaCe(WO4)2 to be used in cold solid state lighting applications. Finally, we also observe that the oxygen vacancies can act as active centers for the adsorption of molecular oxygen, which in consequence leads NaCe(WO4)2 to have gas sensing properties. [ABSTRACT FROM AUTHOR]

This study aims to evaluate agricultural land suitability for vegetable crop farming in the Uttar Dinajpur district. For performing the land suitability, the bivariate statistical techniques like frequency ratio, entropy index, and weights of evidence models are taken into consideration. Influencing parameters such as elevation, slope,geology,geomorphology,streamdensity,rainfall,aquifertype,geohazard,LandUseLandCover(LULC), Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), groundwater level, soil type, topsoil depth, bulk density, Cation Exchange Capacity (CEC), nitrogen, soil pH, Organic Carbon Content (OCC), distance from Krishi Bazar, distance from the road, distance from the river were used. The estimated results show that 16.93% (531.949 sq. km) of the study district is highly suitable for vegetable cultivation, while 26.643% (873.116 sq. km) is moderately suitable, 20.380% (640.337 sq. km) of the geographical land is marginally suitable and 9.341% (293.488 sq. km) is very less suitable for vegetable farming. Models' validation using the ROC curve resulted that the bivariate techniques like frequency ratio (0.927), entropy index (0.888), and weights of evidence (0.907) are highly effective methods for site selection for vegetable farming in the study region. The factors such as soil, rainfall, aquifer type, groundwater level, nitrogen, and distance from Krishi Bazaar are the most influencing parameters to perform the outcome. [ABSTRACT FROM AUTHOR]