Using both analytic and numerical analyses of the Poisson–Nernst–Planck equations, we theoretically investigate the electric conductivity of a conical channel which, in accordance with recent experiments, exhibits a strong non-linear pressure dependence. This mechanosensitive diodic behavior stems from the pressure-sensitive build-up or depletion of salt in the pore. From our analytic results, we find that the optimal geometry for this diodic behavior strongly depends on the flow rate with the ideal ratio of tip-to-base-radii being equal to 0.22 at zero-flow. With increased flow, this optimal ratio becomes smaller and, simultaneously, the diodic performance becomes weaker. Consequently an optimal diode is obtained at zero-flow, which is realized by applying a pressure drop that is proportional to the applied potential and to the inverse square of the tip radius, thereby countering electro-osmotic flow. When the applied pressure deviates from this ideal pressure drop the diodic performance falls sharply, explaining the dramatic mechanosensitivity observed in experiments.

Two distinct energy transfer (ET) mechanisms have been proposed for the conversion of blue to near-infrared (NIR) photons in YAG:Ce 3+ ,Yb 3+ . The first mechanism involves downconversion by cooperative energy transfer, which would yield two NIR photons for each blue photon excitation. The second mechanism of single-step energy transfer yields only a single NIR photon for each blue photon excitation and has been argued to proceed via a Ce 4+ -Yb 2+ charge transfer state (CTS). If the first mechanism were operative in YAG:Ce 3+ ,Yb 3+ , this material would have the potential to greatly increase the response of crystalline Si solar cells to the blue/UV part of the solar spectrum. In this work, however, we demonstrate that blue-to-NIR conversion in YAG:Ce 3+ ,Yb 3+ goes via the single-step mechanism of ET via a Ce 4+ -Yb 2+ CTS. The photoluminescence decay dynamics of the Ce 3+ excited state are inconsistent with Monte Carlo simulations of the cooperative (one-to-two photon) energy transfer, while they are well reproduced by simulations of single-step (one-to-one photon) energy transfer via a charge transfer state. Based on temperature dependent measurements of energy transfer and luminescence quenching we construct a configuration coordinate model for the Ce 3+ -to-Yb 3+ energy transfer, which includes the Ce 4+ -Yb 2+ charge transfer state.

The charging and dissolution of mineral surfaces in contact with flowing liquids are ubiquitous in nature, as most minerals in water spontaneously acquire charge and dissolve. Mineral dissolution has been studied extensively under equilibrium conditions, even though non-equilibrium phenomena are pervasive and substantially affect the mineral-water interface. Here we demonstrate using interface-specific spectroscopy that liquid flow along a calcium fluoride surface creates a reversible spatial charge gradient, with decreasing surface charge downstream of the flow. The surface charge gradient can be quantitatively accounted for by a reaction-diffusion-advection model, which reveals that the charge gradient results from a delicate interplay between diffusion, advection, dissolution, and desorption/adsorption. The underlying mechanism is expected to be valid for a wide variety of systems, including groundwater flows in nature and microfluidic systems.

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We quantitatively explain the diodic and memristive properties of conical ion channels with bipolar surface charges. A modelled iontronic circuit of these channels exhibits neuronal spiking with membrane potentials comparable to mammalian values.