“…Inorganic fluorides, in particular rare earth metal (REM) fluorides, have a unique combination of physicochemical properties: large band gap, low phonon energy (< 400 cm − 1 ), thermal stability, low nonradiative transition scattering rate, high refractive index, low toxicity, and excellent optical operability [1][2][3][4]. Fluorides are widely used as photonics materials, as optical materials that are transparent in the UV-IR range, luminophores; solid-state lasers, scintillators, antireflection coatings, in metallurgy, in separation of uranium isotopes and in many other fields of science and technology [5].…”