Solvent-induced luminescence behavior of Ce/Eu@Gd-MOF for ratiometric detection of D2O in H2O

Abstract

The solvent environment has a significant impact on the luminescence performance of Ln-MOFs, but the related research studies are still limited. In this work, a Ln-MOF using 1,3,5-benzenetricarboxylic acid as ligands and Ce³⁺/Eu³⁺ as luminescence centers was prepared. The photoluminescence behaviors of Ce/Eu@Gd-MOFs were studied in H₂O and D₂O. The emission intensity of the Ce/Eu@Gd-MOFs dispersed in D₂O is improved by 711.19% compared to that dispersed in H₂O. After excluding the effects of solvent reabsorption and pH, the difference in vibrational frequencies of the functional groups in H₂O and D₂O is considered to be the main reason for the enhanced luminescence. Deuterated hydroxyl groups have lower vibrational frequencies than hydroxyl groups, resulting in effective weakening of nonradiative transitions. Vibrational coupling occurs between the deuterated hydroxyl groups, H₃BTC ligands and Ce³⁺, because of the proximity of the vibrational frequency of the deuterated hydroxyl groups and the energy level gaps between H₃BTC ligands and Ce³⁺. This facilitates the energy transfer through vibration–vibration interaction in non-radiative processes. The enhancement in luminescence and energy transfer efficiency of Ce/Eu@Gd-MOFs in D₂O is attributed to the synergistic effect of the above mechanisms. This solvent-induced luminescence behavior of Ce/Eu@Gd-MOFs holds potential as an approach for detecting D₂O in H₂O. The detection sensitivity reaches 0.001%. This study contributes to the understanding of the Ln-MOF luminescence and offers insights into its practical applications.