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The tetravalent-state stability of manganese is of primary importance for Mn4+ luminescence. Double perovskite-structured A2B′B″O6:Mn4+ has been recently prevalent, and the manganese ions are assumed to substitute for the B″(IV–VI)­O6 site to stabilize at the tetravalent charge state to generate far-red emissions. However, some Mn-doped A2B′B″O6-type materials show no or weak luminescence such as typical Ca2MgWO6:Mn. In this work, a cation-pair co-substitution strategy is proposed to replace 2Ca2+ by Na+–La3+ to form Ca2–2x Na x La x MgWO6:Mn. The significant structural distortion appears in the solid solution lattices with the contraction of [MgO6] but enlargement of [WO6] octahedron. We hypothesize that the site occupancy preference of Mn migrates from Mg2+ to W6+ sites. As a result, the effective Mn4+/Mn2+ concentration enhances remarkably to regulate nonluminescence to highly efficient Mn4+-related far-red emission. The optimal CaNa0.5La0.5MgWO6:0.9%Mn4+ shows an internal quantum efficiency of 94% and external quantum efficiency of 82%, reaching up to the top values in Mn4+-doped oxide phosphors. This work may provide a new perspective for the rational design of Mn4+-activated red phosphors, primarily considering the site occupancy modification and tetravalent-state stability of Mn.

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A nanocomposite material consisting of a copper ion-based metal–organic gel (MOG-Cu) and multiwalled carbon nanotubes (MWCNTs) was prepared and served to construct a sensor for electrochemical detection of nitrite. The micromorphology of the MOG-Cu-MWCNT nanocomposite was characterized. The effects of MWCNT doping on the formation of a Cu-based MOG and its electrochemical property for nitrite electro-oxidation were evaluated. It shows that the optimal amount of MWCNTs does not influence the formation and nanofiber structure of the Cu-based MOG but can increase the electrochemical surface area and facilitate the interfacial charge transport. Hence, the oxidation current of nitrite at the MOG-Cu-MWCNT-coated glass carbon electrode (GCE) is considerably enhanced in contrast to the MOG-Cu/GCE. The analytical performances of the MOG-Cu-MWCNTs/GCE for electrochemical detection of nitrite were investigated. Operated in optimum conditions, the oxidation peak current at a potential of about 0.77 V versus a saturated calomel electrode shows direct proportion correlation with concentration of nitrite. The linear range is 0.3–100 μM. The sensor demonstrates fair anti-interference capacity, high sensitivity, a low detection limit (0.086 μM), satisfactory reproducibility, and storage stability, being a valuable tool for the electrochemical monitoring of nitrite in food samples.

At meso-scale, Calcium Silicate Hydrate (C-S-H) can be considered as randomly packed globules (about 4.2nm), which forms the basic unit cell, with water molecules and voids. In this paper, the nanostructures for the globules are developed based on some plausible atomic structures of C-S-H. The mechanical properties for the C-S-H globules are determined through molecular dynamics simulation. Interfaces between the C-S-H globules are also simulated with different amount of water molecules. Key material parameters, e.g., Young's modulus, strength and fracture energy, are obtained. It has been found that longer mean chain length of silicate tends to increase the strength of C-S-H and change the fracture behavior from brittle to ductile failure, in the chain length direction. In the other direction, however, silicate chains do not play an important role while interlayer structure matters. Moreover, pores in the C-S-H nanostructures can considerably reduce the strength of the globule structures in the normal direction to silicate chain but the weakening effect becomes substantially less in silicate chain direction. Further, it has been found that for all types of the interfaces between C-S-H globules, the interface with no extra water molecules has the greatest tensile/shear strength. The mechanical properties obtained in this paper for C-S-H nanostructures and interfaces are necessary inputs to the meso-scale modelling of C-S-H via either granular mechanics, i.e., DEM, or continuum mechanics, i.e., FEM.