Manipulating particle size is a powerful means of creating unprecedented optical properties in metals and semiconductors. Here we report an insulator system composed of NaYbF4:Tm in which size effect can be harnessed to enhance multiphoton upconversion. Our mechanistic investigations suggest that the phenomenon stems from spatial confinement of energy migration in nanosized structures. We show that confining energy migration constitutes a general and versatile strategy to manipulating multiphoton upconversion, demonstrating an efficient five-photon upconversion emission of Tm3+ in a stoichiometric Yb lattice without suffering from concentration quenching. The high emission intensity is unambiguously substantiated by realizing room-temperature lasing emission at around 311 nm after 980-nm pumping, recording an optical gain two orders of magnitude larger than that of a conventional Yb/Tm-based system operating at 650 nm. Our findings thus highlight the viability of realizing diode-pumped lasing in deep ultraviolet regime for various practical applications.

Case studies of extreme weather and climate events are pivotal to understanding their societal impact in the context of sustainability science. To avoid being constrained by the idiosyncrasy of an individual event, a case study must  Ice-coated forest with decapitated trees in southern China.

Lanthanide-doped upconversion nanoparticles with a suitable surface coating are appealing for biomedical applications. Because high-quality upconversion nanoparticles are typically prepared in an organic solvent and passivated by hydrophobic oleate ligands, a convenient and reliable method for the surface modification of upconversion nanoparticles is thus highly desired to satisfy downstream biological investigations. In this work, we describe a facile and versatile strategy for displacing native oleate ligands on upconversion nanoparticles with a diversity of hydrophilic molecules. The ligand-exchange procedure involves the removal of original oleate ligands followed by the attachment of new ligands in a separate step. The successful coating of relevant ligands was confirmed by Fourier transform infrared spectroscopy, thermogravimetry analysis, and ζ-potential measurement. The surface-modified nanoparticles display high stability and good biocompatibility, as revealed by electron microscopy, photoluminescence spectroscopy, and cytotoxicity assessment. Our study demonstrates that functional biomolecules such as biotin can be directly immobilized on the nanoparticle surface using this approach for the quick and effective detection of streptavidin.

Hexagonal phase NaYbF 4 has recently been reorganized as a more efficient host material than NaYF 4 for constructing multiphoton upconversion nanoparticles. However, the synthesis and size control of NaYbF 4 nanoparticles have not been completely fulfilled. This study presents a controlled synthesis of small NaYbF 4 nanoparticles as well as a mechanistic investigation of the nanocrystal growth process. The NaYbF 4 nanoparticles were synthesized in a ternary solvent mixture composed of oleylamine, oleic acid, and 1octadecene by an injection technique. The oleylamine molecule as a surface capping ligand is found to play critical roles in controlling the growth of NaYbF 4 nanoparticles by promoting conversion of the cubic phase intermediates into the hexagonal phase products. Uniform NaYbF 4 nanoparticles with tunable size (from 7 to 70 nm) were readily prepared by controlling a single variable of solvent composition. After coating with NaLuF 4 shells of 10 nm in thickness, the small NaYbF 4 :Er (2%) nanoparticles exhibited an over 700-fold enhancement in red upconversion emission. By introducing Yb 3+ ions into the shells, the oleate-capped NaYbF 4 :Er (2%)@NaLuF 4 :Yb (25%) upconversion nanoparticles showed an inverse thermal quenching above room temperature. The findings described here are expected to provide a general strategy for facile control of particle size and optical property in other nanomaterials systems.

One of the main challenges in additive manufacturing (AM) of medical implants for the treatment of bone tissue defects is to optimise the mechanical and biological performance. The use of post-processing can be a necessity to improve the physical properties of customised AM processed implants. In this study, Ti-6Al-4V coupons were manufactured using selective laser melting (SLM) in two build orientations (vertical and horizontal) and subsequently post-processed using combinations of hot isostatic pressing (HIP), sandblasting (SB), polishing (PL) and chemical etching (CE). The effect of the different post-manufacturing strategies on the tensile and fatigue performance of the SLMed parts was investigated and rationalised by observing the surface topography. Vertically built samples showed higher yield strength (YS) and ultimate tensile strength (UTS) than the horizontal samples, increasing from 760.9 ± 22.3 MPa and 961.3 ± 50.2 MPa in the horizontal condition to 820.09 ± 16.5 MPa and 1006.7 ± 6.3 MPa in the vertical condition, respectively. After the HIP treatment, the ductility was substantially improved in both orientations; by 2.1 and 2.9 folds in the vertical and horizontal orientations, respectively. The vertically built samples demonstrated a superior ductility of 22% following HIP and polishing. Furthermore, chemical etching was found to be the most effective surface post-processing treatment to improve the fatigue performance after HIP, achieving the highest run-out strength of 450 MPa. Most importantly, chemical etching after HIP enhanced the cellular affinity of the surface, in addition to its good fatigue performance, making it a promising post-processing approach for bone implants where tissue integration is needed.