Abstract
There have been numerous studies onemission-color regulation by the adjustment of molar amountsof multiple trivalent lanthanide cations, such as Eu3+, Tb3+,Dy3+, and others, in many types of solid host materials.Although uranyl emission originating from charge-transfertransitions has been well-recognized and investigated for manydecades, as of now there is no report on tunable 4f/5f bimodalemission based on heterobimetallic lanthanide(III) anduranyl(VI) compounds. In most cases, complete energytransfer between uranyl(VI) and lanthanide(III) centers wasobserved. In this work, a series of isotypic-europiumincorporateduranyl coordination polymers, Eu@UO2L(DMF) (L2− = 3,5-pyridinedicarboxylate, denoted as 1−10, whichrepresent the different Eu contents in UO2L(DMF); DMF = N,N-dimethylformamide), has been synthesized by solvothermalreactions. Crystallographic evidence of this series unveiled one-dimensional chains of UO22+ as pentagonal-bipyramidal unit**ridged by pyridinedicarboxylate with no defined, crystallographically unique site containing Eu, even for the products with highconcentrations of Eu in this series. However, emission bands characteristic of Eu3+ were clearly observed in every product alongwith the characteristic uranyl-emission feature when observed with UV−vis fluorescence spectroscopy. Laser-ablationinductively coupled pla**a mass spectrometry indicated that europium was concomitant with uranium, corroborating theincorporation of europium into crystals of UO2L(DMF). Systematic control of the solvent ratio (VH2O/VDMF) in each reactiongives rise to an enrichment of Eu3+ in the interior of UO2L(DMF). In addition, the color of emission of these compoundschanged significantly from bright red to bright green with decreasing Eu content. This phenomenon occurs from the highlyefficient energy transfer between the UO22+ and Eu3+ centers within each sample, providing the first case of a tunable 4f/5fbimodal emission in a mixed 4f/5f-elements-bearing metal−organic-hybrid material.