Multiphoton Phosphorescence of Simple Ketones by Visible-light Excitation and Its Consideration for Active Sensing in Space.

Acetone and butanone were seen to emit blue light around 450 nm when excited in the green by a high intensity pulsed laser. The pathway of this anti-Stokes emission is believed to be multiphoton absorption followed by phosphorescence, with emission being observed in the samples at cryogenic temperatures below their melting point and not seen from either ketone in their cold liquid state. Given the widespread nature of these simple ketones in off-world bodies and their potential importance as an organic resource for Space Resource Utilization, signals which enable the identification and tracing of these materials are of use in applications from remote sensing and mapping to monitoring during extraction processes. While the excitation process has a low efficiency, the ability to use visible light for sensing of these targets has advantages over UV sources, such as the wider availability of high-powered lasers which could be utilized.

Facile Multistep Synthesis of ZnO-Coated ß-NaYF4:Yb/Tm Upconversion Nanoparticles as an Antimicrobial Photodynamic Therapy for Persistent Staphylococcus aureus Small Colony Variants.

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 ß-NaYF4: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), ß-NaYF4:Yb/Tm@ZnO nanoparticles were synthesized. The direct synthesis of ß-NaYF4: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. ß-NaYF4:Yb/Tm@ZIF-8 composites formed using the CTAB-coated UCNPs were then converted into ß-NaYF4:Yb/Tm@ZnO nanoparticles by calcination under carefully controlled conditions. Photoluminescence analysis confirmed the upconversion process for the UCNP core, which allows the ß-NaYF4: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 ß-NaYF4:Yb/Tm@ZnO nanoparticles.

Upconversion Fluorescence in Naturally Occurring Calcium Fluoride.

Fluorine can negatively interfere with leach and smelting processes during mineral processing. 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, a process in which two or more photons are absorbed and one higher-energy photon is emitted, provides a more host-specific fluorescence output, minimizing 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 analyzed by near-infrared excitation and have revealed upconversion fluorescence from rare earth inclusions. Upconversion fluorescence was detected in samples with rare earth concentrations as low as one part per million and is therefore considered a potential new sensing modality for real-time fluorite monitoring.