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 [H₂N(CH₃)₂]₁₀H₃[SeO₄RE₅(H₂O)₇(Se₂W₁₄O₅₂)₂] ? 40H₂O [RE=Ho³⁺ ( 1 ), Er³⁺ ( 2 ), Tm³⁺ ( 3 ), Tb³⁺ ( 4 )] were synthesized. It should be noted that a penta‐RE [SeO₄RE₅(H₂O)₇]¹¹⁺ central core connecting two tetra‐vacant Dawson‐type [Se₂W₁₄O₅₂]^12? subunits generates a dimeric assembly of [SeO₄RE₅ (H₂O)₇(Se₂W₁₄O₅₂)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.