Double-Oxalate-Bridging Tetralanthanide Containing Divacant Lindqvist Isopolytungstates with an Energy Transfer Mechanism and Luminous Color Adjustablility Through Eu3+/Tb3+ Codoping.

Abstract

A double-oxalate-bridging tetra-Gd3+ containing divacant Lindqvist dimeric isopolytungtate Na10[Gd2(C2O4)(H2O)4(OH)W4O16]2·30H2O (Gd4W8) was obtained based on the reaction of Na2WO4·2H2O, H2C2O4, and GdCl3 in aqueous solution. Its dimeric polyoxoanion is established by two divacant Lindqvist [W4O16]8- segments connected by a rectangular tetra-nuclearity [Gd4(C2O4)2(H2O)8(OH)2]6+ cluster. Notably, neighboring trinuclear [Na3O4(H2O)11]5- clusters are interconnected to construct a picturesque 1-D sinusoidal Na-O cluster chain. The most outstanding characteristic is that 1-D sinusoidal Na-O cluster chains combine [Gd2(C2O4)(H2O)4(OH)W4O16]210- polyoxoanions together, giving rise to an intriguing 3-D extended porous framework. The red emitter Eu3+ ions and green emitter Tb3+ ions are first codoped into Gd4W8 to substitute Gd3+ ions for the exploration of the energy transfer (ET) mechanism between Eu3+ and Tb3+ ions and the color-tunable PL property in the isopolytungtate system. The PL emission spectra and decay lifetime measurements of the Eu3+/Tb3+ codoped Gd4W8 system illustrate that under excitation at 370 nm, Tb3+ ions can transfer energy to Eu3+ ions. When the molar concentration of Tb3+ ions is fixed at 0.9 and that of the Eu3+ ions gradually increases from 0.01 to 0.08, the calculated ET efficiency (ηET) from Tb3+ to Eu3+ ions increases from 7.9% for Gd0.36Tb3.6Eu0.04W8 to 67.3% for Gd0.08Tb3.6Eu0.32W8. The energy transfer mechanism (Tb3+ → Eu3+) is a nonradiative dipole-dipole interaction. Furthermore, upon excitation at 370 nm, Eu4W8 and Tb4W8 show visible red- and green-emitting lights, respectively. When codoping trace amounts of Eu3+ ions in Tb4W8, under excitation at 370 nm, Tb3.92Eu0.08W8 displays near white-light emission.