Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [FeIII(S2Me2N3-(Pr,Pr))]+ (2), that reacts with oxo atom donors (PhIO, IBX-ester, and H2O2) to afford a rare example of a singly oxygenated sulfenate, [FeIII(η2-SMe2O)(SMe2)N3(Pr,Pr)]+ (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O)Cys114 proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [FeIIIS2Me2NMeN2amide(Pr,Pr)]− (8), shows that oxo atom donor reactivity correlates with the metal ion’s ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N3−) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O═I-Ph, or an Fe(V)═O remains to be determined.

Herein, the role that point defects have played over the last two decades in realizing solid‐state laser refrigeration is discussed. A brief introduction to the field of solid‐state laser refrigeration is given with an emphasis on the fundamental physical phenomena and quantized electronic transitions that have made solid‐state laser‐cooling possible. Lanthanide‐based point defects, such as trivalent ytterbium ions (Yb3+), have played a central role in the first demonstrations and subsequent development of advanced materials for solid‐state laser refrigeration. Significant discussion is devoted to the quantum mechanical description of optical transitions in lanthanide ions, and their influence on laser cooling. Transition‐metal point defects have been shown to generate substantial background absorption in ceramic materials, decreasing the overall efficiency of a particular laser refrigeration material. Other potential color centers based on fluoride vacancies with multiple potential charge states are also considered. In conclusion, novel materials for solid‐state laser refrigeration, including color centers in diamond that have recently been proposed to realize the solid‐state laser refrigeration of semiconducting materials, are discussed.

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Two-step crystallization mechanisms based on spinodal decomposition followed by nucleation are commonly observed both in the laboratory and in nature. While this pathway may require chemical reactions, subsequent nucleation and growth are often considered as separate, discrete events from the reaction itself. Recent work has also shown a distinct intermediate step involving the formation of an amorphous aggregate. Here we report a novel four-step mechanism in the aqueous synthesis of sodium yttrium fluoride involving 1) the segregation of aqueous ions into a dense liquid phase, 2) the formation of an amorphous aggregate, 3) nucleation of a cubic YF3 phase, and 4) subsequent solid-state diffusion of sodium and fluoride ions to form a final NaYF4 phase. The final step involves a continuous, gradual change of the solid phase’s chemical stoichiometry from YF3 toward NaYF4. Unlike previously studied nucleation and growth mechanisms, the stoichiometry of the final solid phase evolves throughout the crystallization process rather than being determined at nucleation. This novel four-step mechanism provides a new perspective into the nucleation and growth of many other crystalline materials given the ubiquity of nonstoichiometric compounds in nature.

Al, Cu, Ni, Sn, Ti and Zn have been textured by the application of laser ablation. Laser ablation creates structures such as pits, pillars as well as crystalline nanoparticles and aggregations of these nanoparticles. Subsequently these textured substrates are subjected to high-voltage anodization. TiO2 nanotube formation is quite facile conforming to the initial substrate topology, some time also forming nanotube pills. Increased reaction rates induced by ablation induced surface area increase, nanoparticle deposition and lattice defects can aid the growth of new phases, which are dependent on the solution chemistry, e.g. Al2O3 vs (NH4)2AlF4 in switching from an aqueous to an ethylene glycol-based electrolyte. A porous F-doped ZnO film was produced by anodization of an ablated Zn substrate. The structures of films formed in this manner differ from those produced by conventional anodization.

<div>Although solid-state laser-refrigeration recently has been demonstrated to reach cryogenic temperatures in vacuum, to date the solid-state laser refrigeration of materials at elevated pressure conditions has remained unexplored. Here we demonstrate the laser cooling of ytterbium-doped yttirum-lithium-fluoride (10%Yb³⁺:YLiF₄, or Yb:YLF)</div><div>>17K below room temperature at pressures >4 GPa in a diamond anvil cell using lithium fluoride and ice-VII as a quasi-hydrostatic pressure media. Temperature measurements are quantified using a ratiometric-thermometry approach involving a Boltzmann fit to excited states distribution through 4f-4f Stark-level transitions from the Yb³⁺ ions that occur between the ²F_5/2 and ²F_7/2 manifolds. At pressures between 7 and 12 GPa the YLF grains are observed to undergo a martensitic phase transition from a tetragonal scheelite phase (space group I41/a, Z = 4, No. 88) to a monoclinic fergusonite phase (space group I2/a, Z = 4, No. 15) which modifies the crys-</div><div>tal field splitting of the ground- and excited- state manifolds, but is observed to not eliminate laser cooling. Solid-state laser refrigeration at extreme pressures could allow researchers to use rapid photothermal cycling to explore temperature-dependent properties of materials, including electronic-structure phase-transitions, without the need for external cryostats.</div>

<div>Although solid-state laser-refrigeration recently has been demonstrated to reach cryogenic temperatures in vacuum, to date the solid-state laser refrigeration of materials at elevated pressure conditions has remained unexplored. Here we demonstrate the laser cooling of ytterbium-doped yttirum-lithium-fluoride (10%Yb³⁺:YLiF₄, or Yb:YLF)</div><div>>17K below room temperature at pressures >4 GPa in a diamond anvil cell using lithium fluoride and ice-VII as a quasi-hydrostatic pressure media. Temperature measurements are quantified using a ratiometric-thermometry approach involving a Boltzmann fit to excited states distribution through 4f-4f Stark-level transitions from the Yb³⁺ ions that occur between the ²F_5/2 and ²F_7/2 manifolds. At pressures between 7 and 12 GPa the YLF grains are observed to undergo a martensitic phase transition from a tetragonal scheelite phase (space group I41/a, Z = 4, No. 88) to a monoclinic fergusonite phase (space group I2/a, Z = 4, No. 15) which modifies the crys-</div><div>tal field splitting of the ground- and excited- state manifolds, but is observed to not eliminate laser cooling. Solid-state laser refrigeration at extreme pressures could allow researchers to use rapid photothermal cycling to explore temperature-dependent properties of materials, including electronic-structure phase-transitions, without the need for external cryostats.</div>

High-voltage anodization is well known for producing nanostructures such as porous alumina and TiO 2 nanotubes. The formation mechanisms involve an intricate balance between oxide growth and dissolution in which pore initiation and propagation is convoluted with the need for strain relief. Laser ablation with a nanosecond pulsed Nd:YAG laser (532 nm) produces texture e.g. arrays of pillars, macropores and ripples. Nanoparticles produced in the ablation plume can also be deposited on the target or a remote substrate. These substrates are anodized in solutions typically used for porous film and nanotube production (including viscous fluoride-containing electrolytes). A number of metals have been investigated, with emphasis here on Al and Ti as well as Zn. Laser pre-texturing results in the formation of structures unattainable by anodization alone. Deposited nanoparticles of Al and Zn are found to act as seeds for the growth of oxide crystallites that fuse into porous crystallite films.