https://phys.org/news/2018-05-oxyfluoride-compound-photocatalysis.html

The new material has an unusually small band gap of around 2.4 electron volts (eV), meaning that it can absorb visible light with a wavelength of around 500 nanometers (nm). In general, band gaps bigger than 3 eV are associated with inefficient utilization of sunlight, whereas those smaller than 3 eV are desirable for efficient solar energy conversion.

Additionally, the oxyfluoride belongs to a group of compounds that had until now been largely overlooked due to the highest electronegativity of fluorine, a property that essentially ruled them out as candidates for visible light-driven photocatalysts.