Luminescent Dimeric Oxalate-Bridged Eu³⁺/Tb³⁺-Implanted Arsenotungstates: Tunable Emission, Energy Transfer, and Detection of Ba²⁺ Ion in Aqueous Solution

Abstract

Two cases of lanthanide (Ln)-implanted arsenotungstates, K₁₇Na₂H₅[{(As₂W₁₉O₆₇(H₂O))Ln(H₂O)₂}₂(C₂O₄)]·87H₂O (Ln = Eu (<b>1</b>), Ln = Tb (<b>2</b>)) and their codoped derivatives Eu_<i>x</i>Tb_1-<i>x</i>-POM (<i>x</i> = 0.01 (<b>3</b>), <i>x</i> = 0.04 (<b>4</b>), <i>x</i> = 0.1 (<b>5</b>), <i>x</i> = 0.2 (<b>6</b>)) were prepared and further characterized by powder X-ray diffraction, infrared spectra, and thermogravimetric analyses. An X-ray structural analysis of <b>1</b> and <b>2</b> indicates that they both present a dimeric oxalate-bridged Ln³⁺-implanted lanthanide arsenotungstate polyanion structure. Under the O → W LMCT excitation at 265 nm of arsenotungstate polyanions, the emissions of Ln³⁺ ions in <b>1</b> and <b>2</b> are sensitized and the lifetimes are prolonged. Codoped compounds <b>3</b>-<b>6</b> demonstrate a color-tunable emission from green to red by adjusting the Eu³⁺/Tb³⁺ ratio. Emission spectra and time-resolved emission spectroscopic studies were performed for <b>3</b> to further authenticate the energy transfer processes from excited arsenotungstates to the Eu³⁺ and Tb³⁺ metal ions and also between the Eu³⁺ and Tb³⁺ centers. More interestingly, <b>1</b> is an effective fluorescent probe for the recognition and detection of Ba²⁺ 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.