Polymorphism of Erbium Oxyfluoride: Selective Synthesis, Crystal Structure, and Phase-Dependent Upconversion Luminescence

Mechanism of Reductive Fluorination by PTFE-Decomposition Fluorocarbon Gases for WO3

Reductive fluorination, which entails the substitution of O^2- from oxide compounds with F^- from fluoropolymers, is considered a practical approach for preparing transition-metal oxyfluorides. However, the current understanding of the fundamental reaction paths remains limited due to the analytical complexities posed by high-temperature reactions in glassware. Therefore, to expand this knowledgebase, this study investigates the reaction mechanisms behind the reductive fluorination of WO₃ using polytetrafluoroethylene (PTFE) in an Ni reactor. Here, we explore varied reaction conditions (temperature, duration, and F/W ratio) to suppress the formation of carbon byproducts, minimize the dissipation of fluorine-containing tungsten (VI) compounds, and achieve a high fluorine content. The gas-solid reaction paths are analyzed using infrared spectroscopy, which revealed tetrafluoroethylene (C₂F₄), hexafluoropropene (C₃F₆), and iso-octafluoroisobutene (i-C₄F₈) to be the reactive components in the PTFE-decomposition gas during the reactions with WO₃ at 500 °C. CO₂ and CO are further identified as gaseous byproducts of the reaction evincing that the reaction is prompted by difluorocarbene (:CF₂) formed after the cleavage of C═C bonds in i-C₄F₈, C₃F₆, and C₂F₄ upon contact with the WO₃ surface. The solid-solid reaction path is established through a reaction between WO₃ and WO_3-xF_x where solid-state diffusion of O^2- and F^- is discerned at 500 °C.

Controllable Syntheses, Crystal Structure Evolution, and Photoluminescence of Polymorphic Zirconium Oxyfluorides

Precise synthesis of polymorphic phases with similar components but distinct crystal structures is one of the key problems in inorganic chemistry. In this work, we report a fluorination method adopting ZrO₂ as the starting material and NH₄F as the fluoridation agent that can afford multiphases in the Zr-O-F system, including Zr₇O₉F₁₀, Zr₃O₂F₈, ZrO_0.46F_3.08, ZrO_0.33F_3.33, β-ZrF₄, NH₄Zr₂F₉, and NH₄ZrF₅. A preliminary phase formation diagram was established as a function of the fluorination temperature (T), reaction time (t), and F/Zr ratio after systematic optimization of the preparation conditions. Among the as-obtained phases, the detailed crystal structures of Zr₇O₉F₁₀ and ZrO_0.33F_3.33 were refined based on the powder X-ray diffraction patterns. As the F/O ratio increases, the crystal structures of Zr-O-F phases transform gradually from an anion-deficient α-UO₃-related structure of Zr₇O₉F₁₀ to an anion-excess ReO₃-related structure of ZrO_0.33F_3.33. At last, we also prepared Ti-doped ZrO₂, Zr₇O₉F₁₀, ZrO_0.46F_3.08, and ZrO_0.33F_3.33 to study the host-lattice-dependent photoluminescence properties of zirconium oxyfluorides. The four materials show distinct photoluminescence in the UV and visible regions due to different local coordination environments of Zr/Ti. This work demonstrates the low-temperature fluorination method as an efficient route to phase-selective polymorphic metal oxyfluorides, which can be employed in further structure-property relationship studies.

Comparative study on the photoluminescence properties of monoclinic and cubic erbium oxide

As a heavy rare earth oxide, erbium oxide (Er₂O₃) has many attractive properties. Monoclinic Er₂O₃ has useful properties not found in stable cubic Er₂O₃, such as unique optical properties and high radiation damage tolerance. In this study, pure cubic and mixed phase of cubic and monoclinic Er₂O₃ coatings were prepared. Photoluminescence properties of these coatings were characterized by a confocal micro-Raman spectrometer equipped with 325, 473, 514, 532, 633 nm lasers, and the influence of microstructure on the fluorescence properties was analyzed in detail. The room temperature fluorescence peaks of cubic Er₂O₃ were assigned. Furthermore, a novel method for rapid phase identification of Er³⁺ doped cubic and monoclinic rare earth sesquioxides at room temperature was proposed.

Advanced sensing, imaging, and therapy nanoplatforms based on Nd3+-doped nanoparticle composites exhibiting upconversion induced by 808 nm near-infrared light

Malignant tumors are currently the leading cause of death worldwide, followed by cardiovascular and cerebrovascular diseases. Although various methods, such as blood examination, tissue biopsy, and radiography, for tumor detection, exist, these techniques still require further refinement. Researchers have recently explored the use of novel adjuvant methods, specifically luminescence imaging detection, for the detection of tumors. The light-triggered approach is less invasive and induces fewer side effects than traditional detection methods. This paper highlights recent advances in the design, property tuning, and applications of nanoparticles that exhibit upconversion under 808 nm excitation. When doped with neodymium ions, upconverted nanoparticles gain the ability to absorb 808 nm light. The advantageous unique features of 808 nm light include deep tissue penetration and limited thermal side effects. The 808 nm-excited upconverted nanoparticles exhibit superior potential for use in biosensing, bioimaging, therapy, and three-dimensional display. Thus, innovative theranostic nanoplatforms can be developed by incorporating 808 nm-excited upconverted nanoparticles with phototherapy agents. Such a composite technique is expected to possess the individual advantages of each material.