Nanoscale structuralisation is demonstrated to influence the stability and catalytic properties of zeolitic imidazolate framework-8.

No abstract

Understanding the upconversion pathways of a rare‐earth dopant is crucial to furthering the use of that material, either toward applications in imaging or elsewhere. This work outlines a new analysis approach that consists of using two synchronized widely‐tunable laser sources to explore the properties of upconverting materials. By examining sensitizer‐free rare‐earth nanoparticles based on a matrix of hexagonal sodium yttrium tetrafluoride (β‐NaYF4) doped with praseodymium but no ytterbium sensitizer, a “non‐degenerate” two‐color upconversion fluorescence at a combined excitation of 1020–850 nm is shown. This insight demonstrates the ability of this technique to locate and interrogate novel upconversion pathways. The dopant level of the nanoparticles could be modified without altering other factors, such as the particle's shape or size, that would also change optical properties and this allows investigation of the dopant‐level dependency of the optical properties. The approach also allows exploration of the time delay domain between the arrival times of the two non‐degenerate excitation pulses, which allows modulation of the brightness from the visible light emissions. This work opens up the parameter space for the systematic synthesis and characterization of new materials with non‐degenerate upconversion emission.

Antibacterial treatment strategies using functional nanomaterials, such as photodynamic therapy, are urgently required to combat persistent Staphylococcus aureus small colony variant (SCV) bacteria. Using a stepwise approach involving thermolysis to form β-NaYF 4 :Yb/Tm upconversion nanoparticles (UCNPs) and surface ligand exchange with cetyltrimethylammonium bromide (CTAB), followed by zeolite imidazolate framework-8 (ZIF-8) coating and conversion to zinc oxide (ZnO), β-NaYF 4 :Yb/Tm@ ZnO nanoparticles were synthesized. The direct synthesis of β-NaYF 4 :Yb/Tm@ZIF-8 UCNPs proved problematic due to the hydrophobic nature of the as-synthesized material, which was shown by zeta potential measurements using dynamic light scattering (DLS). To facilitate deposition of a ZnO coating, the zeta potentials of (i) as-synthesized UCNPs, (ii) calcined UCNPs, (iii) polyvinylpyrrolidone (PVP), and (iv) CTAB-coated UCNPs were measured, which revealed the CTAB-coated UCNPs to be the most hydrophilic and the better-dispersed form in water. β-NaYF 4 :Yb/Tm@ZIF-8 composites formed using the CTAB-coated UCNPs were then converted into β-NaYF 4 :Yb/Tm@ZnO nanoparticles by calcination under carefully controlled conditions. Photoluminescence analysis confirmed the upconversion process for the UCNP core, which allows the β-NaYF 4 :Yb/Tm@ZnO nanoparticles to photogenerate reactive oxygen species (ROS) when activated by near-infrared (NIR) radiation. The NIR-activated UCNPs@ZnO nanoparticles demonstrated potent efficacy against both Staphylococcus aureus (WCH-SK2) and its associated SCV form (0.67 and 0.76 log colony forming unit (CFU) reduction, respectively), which was attributed to ROS generated from the NIR activated β-NaYF 4 :Yb/Tm@ZnO nanoparticles.

Fluorine can negatively interfere with leach and smelting processes during mineral processing1,2. Real-time knowledge of the concentration and mineral hosts of fluorine in a mineral processing ore stream is important to protect process line equipment and product. Currently only offline methods of detection are available. Online sensors that determine specific fluorine-bearing mineral concentration in real-time would enable improved efficiency in processing decisions during mine production. Common excitation wavelengths used for fluorescence studies in minerals frequently provide signals that are not clearly host-specific, and hence of limited utility for mineral identification. We show that upconversion fluorescence (UF), a process in which two or more photons are absorbed and one higher-energy photon is emitted, provides a more host-specific fluorescence output, minimising spurious signals in complex environments and therefore greatly improving detection thresholds. Natural samples of fluorite (CaF2), a major fluorine host at many mine sites, have been analysed by near-infrared excitation and have revealed UF from rare earth inclusions. UF was detected in samples with rare earth concentrations as low as 1 part per million, and is therefore considered a potential new sensing modality for real-time fluorite monitoring.