| http://www.w3.org/ns/prov#value | - Still another technique reported, only for the preparation of europium activated lanthanum, gadolinium, yttrium and lutetium oxysulfides, is the solid state reaction between the mixed rare earth oxides (activator and host) and a composition such as alkali metal carbonates and sulfur which produces alkali metal sulfides and polysulfides, which in turn react at elevated temperatures with the rare ea
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