Single-crystal growth, structure and luminescence properties of Cs₂HfCl₃Br₃

Single crystal of the mixed-halogen compound Cs₂HfCl₃Br₃ was grown by the vertical Bridgman method, and we investigated its crystal structure and optical properties. Single-crystal X-ray diffraction and energy dispersive X-ray spectroscopy analyses indicated the chemical composition to be Cs₂Hf(Cl_0.578(6)Br_0.422(6))₆ (= Cs₂HfCl_3.47(4)Br_2.53(4), approximately Cs₂Hf(Cl_{0 58}Br_0.42)₆) where the number in the parentheses denotes the estimated standard deviation in the last digit. Cs₂Hf(Cl_0.58Br_0.42)₆ was found to have a cubic Fm3‾m potassium hexachloroplatinate structure consisting of Cs⁺ cations and Hf(Cl_{0 . 58}Br_0.42)₆ ²⁻ anions. The emission peak of Cs₂HfCl₃Br₃ was red-shifted by Br substitution, and the photoluminescence decays of Cs₂HfCl₃Br₃ were accelerated when compared to those of Cs₂HfCl₆. Cs₂HfCl₃Br₃ had an emission peak at 450 nm under X-ray irradiation, while under UV-excitation, two photoluminescence emission peaks at 420 and 525 nm were observed. The decay profile of the 420-nm emission band had a single-exponential component with a decay time of 1.95 ± 0.01 μs under the 280-nm-excitation. On the other hand, 525-nm-emisison had two decay components of 0.28 ± 0.03 μs (11%) and 6.54 ± 0.03 μs (89%) under 305-nm-photons excitation.