“…The present result indicates that the substitution of Dy 3+ for Y 3+ did not influence the phase and crystal structure of tetragonal NaY(WO 4 ) 2 . This is because the radius of Dy 3+ (0.1027 nm for dodecahedron site) is almost the same as that of Y 3+ (0.102 nm for dodecahedron site), Dy 3+ can easily enter into the eightfold coordination Y 3+ sites of S 4 point symmetry [25,26]. Actually, it is due to the similar radius and properties among lanthanide ions Eu 3+ , Tb 3+ , Dy 3+ , Y 3+ , La 3+ , etc., and the unique structure of double alkaline rare-earth tungstates ARe(WO 4 ) 2 , the high concentration Ln 3+ ions can easily enter into the ARe(MO 4 ) 2 lattice substituting for the Re 3+ cations and keep the single phase of ARe(MO 4 ) 2 .…”