1. B. P.Sobolev , The Rare Earth Trifluorides, Part 1: The High Temperature Chemistry of the Rare Earth Trifluorides , (Institute of Crystallography, Moscow, 2000; Institut d'Estudis Catalans , Barcelona , 2000 )
2. V. M.Goldschmidt , T.Barth , G.Lunde and W.Zachariasen , Geochemische Verteilungsgesetze der Elemente, VII, Skrift Norske Vid. Acad. Oslo, I, Mat.-Nat. klasse. , 1926 , vol. 1 ( 2 ), p. 1
3. Modification of the Optical Properties of CaF2TR3+ Crystals by Yttrium Impurities