Luminescence and Scintillation of [Nb 2 O 2 F 9 ] 3- -Dimer-Containing Oxide-Fluorides: Cs 10 (Nb 2 O 2 F 9 ) 3 F, Cs 9.4 K 0.6 (Nb 2 O 2 F 9 ) 3 F, and Cs 10 (Nb 2 O 2 F 9 ) 3 Cl.

We report three novel Nb-containing oxide-fluorides, Cs 10 (Nb 2 O 2 F 9 ) 3 F, Cs 9.4 K 0.6 (Nb 2 O 2 F 9 ) 3 F, and Cs 10 (Nb 2 O 2 F 9 ) 3 Cl, 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 P 3̅ m 1. All three compositions form the same framework structure consisting of isolated [Nb 2 O 2 F 9 ] 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 Cs 10 (Nb 2 O 2 F 9 ) 3 F. The broad band emission of these compounds is attributed to the charge-transfer transitions of Nb-O bonds within the [Nb 2 O 2 F 9 ] 3- dimers. All three compounds scintillate blue under X-ray irradiation. Radioluminescence (RL) measurements performed on Cs 10 (Nb 2 O 2 F 9 ) 3 F demonstrate that the RL emission intensity decreases with increasing temperature and that the integrated RL emission (300-750 nm) is 4% of Bi 4 Ge 3 O 12 (BGO) powder. Thermogravimetric analysis confirms that Cs 10 (Nb 2 O 2 F 9 ) 3 F has excellent thermal stability up to 600 °C and no structural phase transition is observed prior to sample decomposition.