Tetrametallic Terbium/Europium Fluorenylphosphonate With Excellent X-Ray Scintillating and Photo-Induced Luminescence

This work reports two lanthanide clusters, [Ln₄(RPO₃)₂(RPO₃H)(^tBuCO₂)₇(^tBuCO₂H)₃(H₂O)₃] (Ln = Eu, Tb; RPO₃H₂ denotes (9-methyl-9H-fluoren-9-yl)phosphonic acid). A comprehensive series of characterizations was performed for the Eu₄ and Tb₄ clusters, including X-ray crystallography, X-ray scintillation, and photoluminescence spectroscopy, to elucidate their structural features and physicochemical properties. Notably, these clusters exhibit exceptional X-ray scintillation performance, attributed to the characteristic luminescence of Ln³⁺ ions. This finding paves the way for the development of novel scintillator materials and enriches the family of lanthanide-bearing clusters with X-ray scintillating properties. Furthermore, photoluminescence modulation was achieved for the chemically mixed Eu/Tb analogues, c-Eu_xTb_4-x (x = 2.67, 2, 1.33), and physically mixed Eu₄/Tb₄ materials, p-yEu₄:zTb₄ (y:z = 2:1, 1:1, 1:2), with varying the excitation wavelength. Notably, near-white-light emission is realized for p-Eu₄:2Tb₄ upon excitation at 365 nm. Collectively, these tetranuclear lanthanide phosphonates exhibit excitation-wavelength and Eu³⁺:Tb³⁺ ratio dependent luminescence, indicating their potential as color-tunable luminescent materials and white-light-emitters.