Red-emission over a wide range of wavelengths at various temperatures from tetragonal BaCN2:Eu2+Electronic supplementary information (ESI) available: Crystallographic Data (CSD 434273) in CIF format, powder XRD, lattice parameters. See DOI: 10.1039/c8tc01289j

A new polymorph of BaCN 2 was obtained via a simple nitridation reaction of BaCO 3 under an NH 3 flow at 900 °C. The product was analyzed via single crystal X-ray diffraction and infrared spectroscopy, and it was found to have a tetragonal I 4/ mcm crystal structure (space group no. 140) with a = 0.60249(4) nm and c = 0.71924(5) nm. In this structure, each Ba 2+ cation is situated in the square antiprism of N atoms of NCN 2− anionic groups. Eu 2+ doped BaCN 2 can be excited by irradiation of blue and green light (from 400 to 550 nm), and it generates an intense red emission peak at 660 nm with a quantum efficiency of 42% in response to 465 nm excitation at room temperature. The peak emission wavelength varies over an extremely wide range of temperature, from 640 nm at 500 K to 680 nm at 80 K, and this red-shift with decreasing temperature is attributed to a unit cell shrinkage that results in significant crystal field splitting of the 5d energy levels of the Eu 2+ ions. A new tetragonal BaCN 2 polymorph was obtained via a simple nitridation reaction of BaCO 2 , and the Eu doped product showed a red emission with an extremely wide range of red-shift of the emission wavelength with decreasing temperature.