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The hydrothermal synthesis and characterization of 10%Yb3+:LiLuF4 (LLF) microcrystals are reported. A combination of X‐ray diffraction (XRD) analysis, analytical transmission electron microscopy (TEM), scanning TEM (STEM), energy‐dispersive X‐ray (EDX) spectroscopy), temperature‐dependent Fourier‐transform infrared (FTIR) spectroscopy, and photoluminescence (PL) measurements confirm a scheelite (I41/a) phase and substitutional doping of Yb3+ within the microcrystals. Laser cooling to more than 20 K below room temperature in vacuum (10−3 torr) is demonstrated when irradiating individual microcrystals using a near‐infrared pumping wavelength (λ = 1020nm) at a laser power of 40 mW (irradiance of 0.85 MW cm−2). The use of these microcrystals is further demonstrated for solid‐state laser refrigeration of an electron‐transparent silicon‐nitride (Si3N4) TEM window. A combination of internal luminescence thermometry, heat‐transfer modeling, and control measurements on lithographically patterned Si3N4 optical cavities is used to demonstrate successful bulk laser cooling of Si3N4 TEM windows by ≈15 K below room temperature, opening new opportunities for contactless in situ TEM refrigeration. [ABSTRACT FROM AUTHOR]

Alkaline zinc-manganese dioxide (Zn-MnO 2 ) batteries are well suited for grid storage applications because of their inherently safe, aqueous electrolyte and established materials supply chain, resulting in low production costs. With recent advances in the development of Cu/Bi-stabilized birnessite cathodes capable of the full 2-electron capacity equivalent of MnO 2 (617 mA h/g), there is a need for selective separators that prevent zincate (Zn(OH) 4 ) 2- transport from the anode to the cathode during cycling, as this electrode system fails in the presence of dissolved zinc. Herein, we present the synthesis of N -butylimidazolium-functionalized polysulfone (NBI-PSU)-based separators and evaluate their ability to selectively transport hydroxide over zincate. We then examine their impact on the cycling of high depth of discharge Zn/(Cu/Bi-MnO 2 ) batteries when inserted in between the cathode and anode. Initially, we establish our membranes' selectivity by performing zincate and hydroxide diffusion tests, showing a marked improvement in zincate-blocking ( D Zn (cm 2 /min): 0.17 ± 0.04 × 10 -6 for 50-PSU, our most selective separator vs 2.0 ± 0.8 × 10 -6 for Cellophane 350P00 and 5.7 ± 0.8 × 10 -6 for Celgard 3501), while maintaining similar crossover rates for hydroxide ( D OH (cm 2 /min): 9.4 ± 0.1 × 10 -6 for 50-PSU vs 17 ± 0.5 × 10 -6 for Cellophane 350P00 and 6.7 ± 0.6 × 10 -6 for Celgard 3501). We then implement our membranes into cells and observe an improvement in cycle life over control cells containing only the commercial separators (cell lifetime extended from 21 to 79 cycles).

The development of upconversion nanomaterials for many photonic applications requires a detailed understanding of their radiative lifetimes that in turn depend critically on local environmental conditions. In this work, hexagonal (β-phase) sodium-yttrium-fluoride (NaYF 4 ) nanowires (NWs) were synthesized and substitutionally co-doped with a luminescent solid solution of trivalent erbium and ytterbium ions. A single-beam laser trapping instrument was used in tandem with a piezo-controlled, variable-temperature stage to precisely vary the nanowire's distance from the substrate. The spontaneous photoluminescence lifetime of the 4 S 3/2 → 4 I 15/2 transition from Er 3+ ions was observed to change by >60% depending on the ions' separation distance from a planar (water/glass) dielectric interface. The 4 S 3/2 state lifetime is observed to increase by a factor of 1.62 ± 0.01 as the distance from the quartz coverslip increases from ∼0 nm to ∼40 μm. Less significant changes in the luminescence lifetime (≤10%) were observed over a temperature range between 25 and 50 °C. The distance dependence of the lifetime is interpreted quantitatively in the context of classical electromagnetic coupling between Er 3+ ions within the nanowire and the adjacent dielectric interface. We also demonstrate potential applications of the NaYF 4 NWs for both controlling and probing temperatures at nanometer scales by integrating them within a poly(dimethylsiloxane) composite matrix.