Luminescent Dimeric Oxalate-Bridged Eu 3+ /Tb 3+ -Implanted Arsenotungstates: Tunable Emission, Energy Transfer, and Detection of Ba 2+ Ion in Aqueous Solution.

Two cases of lanthanide (Ln)-implanted arsenotungstates, K 17 Na 2 H 5 [{(As 2 W 19 O 67 (H 2 O))Ln(H 2 O) 2 } 2 (C 2 O 4 )]·87H 2 O (Ln = Eu ( 1 ), Ln = Tb ( 2 )) and their codoped derivatives Eu x Tb 1- x -POM ( x = 0.01 ( 3 ), x = 0.04 ( 4 ), x = 0.1 ( 5 ), x = 0.2 ( 6 )) were prepared and further characterized by powder X-ray diffraction, infrared spectra, and thermogravimetric analyses. An X-ray structural analysis of 1 and 2 indicates that they both present a dimeric oxalate-bridged Ln 3+ -implanted lanthanide arsenotungstate polyanion structure. Under the O → W LMCT excitation at 265 nm of arsenotungstate polyanions, the emissions of Ln 3+ ions in 1 and 2 are sensitized and the lifetimes are prolonged. Codoped compounds 3 - 6 demonstrate a color-tunable emission from green to red by adjusting the Eu 3+ /Tb 3+ ratio. Emission spectra and time-resolved emission spectroscopic studies were performed for 3 to further authenticate the energy transfer processes from excited arsenotungstates to the Eu 3+ and Tb 3+ metal ions and also between the Eu 3+ and Tb 3+ centers. More interestingly, 1 is an effective fluorescent probe for the recognition and detection of Ba 2+ ions in aqueous solution. The optical properties of the Ln-implanted arsenotungstate compounds not only expressly reveal distinctive energy transfer processes in those compounds but also broaden the application of POM-based materials in the fluorescence sensing field.