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Fluorides are promising host materials for optical applications. This paper reports the photoluminescent (PL) and cathodoluminescent (CL) characteristics of barium hexafluorogermanate BaGeF 6 nanowires codoped with Ce 3+ , Tb 3+ and Sm 3+ rare earth ions, produced by a solvothermal route. The synthesized BaGeF 6 nanowires exhibit uniform morphology and size distribution. X-ray diffraction divulges the one-dimensional growth of crystalline BaGeF 6 structure, with the absence of any impurity phases. Visible luminescence is recorded from the nanowires in green and red regions, when the nanowires are codoped with Ce 3+ /Tb 3+ , and Ce 3+ /Tb 3+ /Sm 3+ , respectively, under a UV excitation source. The PL emission from the codoped BaGeF 6 nanowires, when excited by a 254 nm source, originates from the efficient energy transfer bridges between Ce 3+ , Tb 3+ and Sm 3+ ions. The decay time of the visible luminescent emission from the nanowires is in the order of subnanoseconds, being one of the shortest decay time records from inorganic scintillators. The CL emission from the BaGeF 6 nanowires in the tunable visible range reveals their potential use for the detection of high-energy radiation. The PL emissions are sensitive to H 2 O 2 at low concentrations, enabling their high-sensitivity detection of H 2 O 2 using BaGeF 6 nanowires. A comparison with BaSiF 6 nanowires is made in terms of decay time and its sensitivity towards H 2 O 2 . 

We describe a strategy of integrating quantum mechanical (QM), hybrid quantum mechanical/molecular mechanical (QM/MM) and MM simulations to analyze the physical properties of a solid/water interface. This protocol involves using a correlated ab initio (CCSD(T)) method to first calibrate Density Functional Theory (DFT) as the QM approach, which is then used in QM/MM simulations to compute relevant free energy quantities at the solid/water interface using a mean-field approximation of Yang et al. that decouples QM and MM thermal fluctuations; gas-phase QM/MM and periodic DFT calculations are used to determine the proper QM size in the QM/MM simulations. Finally, the QM/MM free energy results are compared with those obtained from MM simulations to directly calibrate the force field model for the solid/water interface. This protocol is illustrated by examining the orientations of an alkyl amine ligand at the gold/water interface, since the ligand conformation is expected to impact the chemical properties ( e.g. , charge) of the solid surface. DFT/MM and MM simulations using the INTERFACE force field lead to consistent results, suggesting that the effective gold/ligand interactions can be adequately described by a van der Waals model, while electrostatic and induction effects are largely quenched by solvation. The observed differences among periodic DFT, QM/MM and MM simulations, nevertheless, suggest that explicitly including electronic polarization and potentially charge transfer in the MM model can be important to the quantitative accuracy. The strategy of integrating multiple computational methods to cross-validate each other for complex interfaces is applicable to many problems that involve both inorganic/metallic and organic/biomolecular components, such as functionalized nanoparticles. 

Inorganic materials with short radiative decay time are highly desirable for fast optical sensors. This paper reports fast photoluminescence (PL) from a series of barium hexafluorosilicate (BaSiF 6 ) superlong nanowires with high aspect ratios, codoped with Ce 3+ /Tb 3+ /Eu 3+ ions, with a subnanosecond decay time. Solvothermally synthesized BaSiF 6 nanowires exhibit a uniform morphology, with an average diameter less than 40 nm and aspect ratios of over several hundreds, grown in the c -axis direction with {110} surfaces. The PL emission from the codoped BaSiF 6 nanowires, when excited by a 254 nm source, is dependent on Tb 3+ concentration, and the energy transfer from Ce 3+ to Tb 3+ and to Eu 3+ ions allows efficient emissions in the visible spectra when excited by a near UV source. Annealing BaSiF 6 nanowires at 600 °C in a vacuum produced barium fluoride (BaF 2 ) nanowires composed of nanocrystals. Both BaSiF 6 and BaF 2 nanowires exhibit fast emissions in the visible spectra, with enhanced intensities compared with their codoped microparticle counterparts. The decay time of codoped BaSiF 6 nanowires is found to be shorter than that of codoped BaF 2 nanowires. The energy transfer is also observed in their cathodoluminescence spectra with high-energy irradiation.