Two Eu-Doped Polyoxotungstates with Distinct Structures for Multifunctional Integration of Photoluminescence, Proton Conductivity and Resistive Switching

Abstract

The growing demand for multifunctional integrated materials in fields such as optoelectronics and energy storage has driven research into novel composite materials that combine structural tunability with synergistic properties. Two Eu(III)-doped germanotungstate clusters, a tetrameric cluster H22[H2N(CH3)2]2Na2[Na(H2O)][K(H2O)][K(H2O)2]2{Eu2(EuO)2[Eu2(WO4)]2(WO6)}[α(1, 3)-GeW10O37]4·12H2O (1-Eu) and an octameric cluster H12[H2N(CH3)2]Na[Na(H2O)]K5[K(H2O)]2{Eu18(Eu2O)(EuO2)[EuO(H2O)](SeO3)24}[α(10, 12)-GeW10O37]8·28H2O (2-Eu), were successfully synthesized via a precursor-directed strategy. The structural evolution from the tetramer (1-Eu) to the octamer (2-Eu) results in a more intricate cluster cage architecture and a more extensive hydrogen-bonding network. This molecular-level control leads to an improvement in performance: the photoluminescence lifetime increases from 481.4 μs to 818.5 μs, the quantum yield rises substantially from 15.39% to 93.36%, the proton conductivity at 98% RH and 85 °C shows a moderate improvement from 6.10×10-3 S·cm–1 to 6.58×10-3 S·cm–1, and the resistive switching behavior transitions from write-once-read-many (WORM) to reversible bipolar switching with an ON/OFF ratio exceeding 104. These results highlight that deliberate structural design at the cluster level enables the synergistic optimization of multiple functionalities, thereby providing new experimental and theoretical foundations for developing polyoxotungstate -based multifunctional materials.