Luminescence and Scintillation of [Nb₂O₂F₉]^3–-Dimer-Containing Oxide–Fluorides: Cs₁₀(Nb₂O₂F₉)₃F, Cs_9.4K_0.6(Nb₂O₂F₉)₃F, and Cs₁₀(Nb₂O₂F₉)₃Cl

Abstract

We report three novel Nb-containing oxide–fluorides, Cs10(Nb2O2F9)3F, Cs9.4K0.6(Nb2O2F9)3F, and Cs10(Nb2O2F9)3Cl, which were prepared as high-quality single crystals via a HF-based mild hydrothermal route. The compounds all crystallize in the trigonal crystal system with space group P3̅m1. All three compositions form the same framework structure consisting of isolated [Nb2O2F9]3– dimers that create hexagonal channels that are occupied by disordered halide species. Upon excitation by UV light at room temperature, these compounds display broad band emission with a maximum at 440 nm for Cs10(Nb2O2F9)3F. The broad band emission of these compounds is attributed to the charge-transfer transitions of Nb–O bonds within the [Nb2O2F9]3– dimers. All three compounds scintillate blue under X-ray irradiation. Radioluminescence (RL) measurements performed on Cs10(Nb2O2F9)3F demonstrate that the RL emission intensity decreases with increasing temperature and that the integrated RL emission (300–750 nm) is 4% of Bi4Ge3O12 (BGO) powder. Thermogravimetric analysis confirms that Cs10(Nb2O2F9)3F has excellent thermal stability up to 600 °C and no structural phase transition is observed prior to sample decomposition.

Exploiting the Reactivity of Metal Trifluoroacetates to Access Alkali–Niobium(V) Oxyfluorides

“…Mixed-metal oxyfluorides containing d 0 ions from groups V and VI illustrate the significance of exploratory synthesis in materials research. These oxyfluorides feature [MO n F m ] (M = Nb 5+ , Ta 5+ , Mo 6+ , W 6+ ) building blocks whose connectivity, electronic structure, and/or coordination geometry bring about functionalities such as ionic transport, , nonlinear-optical activity, , scintillation, and photoluminescence. , Examples of functional oxyfluorides discovered through exploratory synthesis include (Li, Na, Rb)­SrNb 2 O 6 F, KMoO 2 F 3 , BaWO 2 F 4 , and Cs 10 (Nb 2 O 2 F 9 ) 3 F . Synthetic efforts toward these and other compositions encompass a broad range of methodologies (e.g., solid-state reaction in metal tubes, , high-pressure/high-temperature solid-state reaction, and hydrothermal , ) and fluorine sources (e.g., metal fluoride salts, , fluorinated polymers, aqueous HF, , and fluorine gas).…”

Comparative Study on Crystal Structures and Synthetic Techniques of Ternary Hafnium/Zirconium Fluorides

“…For the hydrothermal route using aqueous HF, we established that mild conditions, 160–200 °C and relatively short reaction times, 24 h, followed by slow cooling to room temperature, often yielded high-quality crystals of ternary and quaternary fluorides whose structures could readily be determined. We have used this approach to explore, in general, the preparation of transition metal- and rare earth-containing fluorides and oxyfluorides, including vanadates, niobates, tantalates, tungstates, molybdates, manganates, cobaltates, nickelates, and cerates, as well as numerous actinide-containing fluoride phases containing Th, U, Np, Pu, and Am. ,,− ,− During this process, by experience, we have learned much about how to choose the optimum reaction conditions. In recent work, we explored hafnium fluorides, which yielded a number of hydrated phases, including Cs 2 [M­(H 2 O) 6 ]­[Hf 2 F 12 ] (M = Ni, Co, and Zn) and CuHfF 6 (H 2 O) 4 .…”