Preparations, Structures and Luminescence Properties of Penta-rare-earth Incorporated Tetravacant Dawson Selenotungstates and Their Ho3+ /Tm3+ Co-doped Derivatives.

A family of penta-rare-earth incorporated tetravacant Dawson selenotungstates [H2 N(CH3 )2 ]10 H3 [SeO4 RE5 (H2 O)7 (Se2 W14 O52 )2 ] ⋅ 40H2 O [RE=Ho3+ (1), Er3+ (2), Tm3+ (3), Tb3+ (4)] were synthesized. It should be noted that a penta-RE [SeO4 RE5 (H2 O)7 ]11+ central core connecting two tetra-vacant Dawson-type [Se2 W14 O52 ]12- subunits generates a dimeric assembly of [SeO4 RE5 (H2 O)7 (Se2 W14 O52 )2 ]13- in the structures of 1-4. Meanwhile, a class of Ho3+ /Tm3+ co-doped derivatives based on 1 with a Ho3+ /Tm3+ molar ratio of 0.75:0.25-0.25:0.75 were also prepared and characterized by energy-dispersive spectroscopy (EDS) analyses. Moreover, their luminescence properties were systematically investigated, which indicate that Tm3+ ions can sensitize the emission of Ho3+ ions in the visible region and prolong the fluorescence lifetime of Ho3+ ions to some extent. Energy transfer from Tm3+ ions to Ho3+ ions was probed by time-resolved emission spectroscopy (TRES), and the CIE 1931 diagram has been applied to evaluate all possible luminescence colors.