[en] This patent describes a process for producing metal fluorides for low optical loss glass applications selected from the group. It comprises: aluminum trifluoride, hafnium tetrafluoride and zirconium tetrafluoride. The steps comprise: incompletely reacting reactants of a fluorinating agent selected from the group consisting of F₂, NF₃, N₂F₂, N₂F₄, ClF₃, BrF₃, IF₅ and SF₄ and a metal selected from the group consisting of aluminum, hafnium and zirconium, or the corresponding metal's compound to produce a reaction product comprising the metal fluoride and at least an amount of the residual metal or its compound effective to react with any metal fluoride impurities in the reactants, and separating the metal fluoride from the reaction product by heating the reaction product to selectively vaporize the metal fluoride for separate recovery from the reaction product and to react the residual metal or its compound with the metal fluoride impurities