Protective metal oxy-fluoride coatings

A thin film comprising:

• a metal oxy-fluoride having an empirical formula of MxOyFz, where M is a metal comprising at least one of aluminum, calcium, or strontium, y has a value of 0.1 to 1.9 times a value of x and z has a value of 0.1 to 3.9 times the value of x;
• wherein the thin film has a thickness of 1 to 30 microns and a porosity of less than 0.1%, and
• wherein one of:
• the metal has a valence of 2 and the metal oxy-fluoride comprises approximately 37-48 at. % of the metal, approximately 10-43 at. % oxygen, and approximately 10-53 at. % fluorine,
• the metal has a valence of 3 and the metal oxy-fluoride comprises approximately 27-38 at. % of the metal, approximately 10-52 at. % oxygen, and approximately 10-63 at. % fluorine, or
• the metal has a valence of 4 and the metal oxy-fluoride comprises approximately 22-32 at. % of the metal, approximately 10-58 at. % oxygen, and approximately 10-68 at. % fluorine.