Energy Transfer in Eu x Gd 1– x (OH) 3,am

High Resolution Image Download MS PowerPoint Slide This study examined the luminescence properties and quenching mechanism in amorphous Eu(OH) 3 and Eu x Gd 1– x (OH) 3 under alkaline conditions (pH 12.5) representative of cement porewaters. Different Gd(III) contents were used to alter the average Eu(III)–Eu(III) distances in the amorphous solids. Gd(III) was considered “inert” due to the similar ionic radius and lack of spectral overlap between Eu(III) and Gd(III). The Eu(III) luminescence was investigated using time-resolved laser-induced luminescence spectroscopy (TRLFS), and the luminescence decay curves were analyzed according to the Inokuti–Hirayama model. It was found that the luminescence quenching in the investigated materials is primarily caused by energy migration between Eu(III) ions best described by dipole–dipole interactions with an estimated critical Eu(III)–Eu(III) distance R 0 of 5.8 ± 0.3 Å. Temperature-dependent experiments revealed that the quenching efficiency significantly decreased below 250 K, indicating that Eu(III) ions in thermally populated 7 F 1 and 7 F 2 levels take part in the energy migration. Employing the RET pair Tb(III)/Eu(III) in Tb x Eu 0.0005 x Gd 1– x (OH) 3 offered additional evidence that interlanthanide energy transfer occurs in the amorphous lanthanide hydroxides. In addition, concentration-independent quenching processes, such as energy transfer to vibrational overtones of OH – or H 2 O, were observed. These findings contribute to understanding the photophysics of amorphous lanthanide hydroxides and may also offer insights into other Eu(III)-rich phases that may form under conditions relevant for nuclear waste repositories.