Fluorescence-Based Aqueous Phosphate Sensing Using Eu(cpboda)(DMF)2

Abstract

Fluorescence-based phosphate sensing using phosphate-sensitive phosphors is a promising approach for in situ monitoring of phosphate pollution in waterways and reservoirs. To date, the most sensitive phosphor developed for this purpose is Tb(cpboda)(DMF)2, where cpboda = (3,3′-((5-Carboxy-1,3-phenylene)bis(oxy))dibenzoic acid). In this study, we further improve this sensitivity by replacing the Tb3+ ions with Eu3+ ions to make Eu(cpboda)(DMF)2 and find concentration-independent phosphate-sensitivity of 1570 ± 120, which is ≈8× more sensitive than the Tb-version. This improvement is attributed to Eu3+ having a hypersensitive transition, while Tb3+ does not. Additionally, we characterize the phosphor’s optical properties, photodegradation, and water solubility. We find that the phosphor presents challenges with regards to both photodegradation and solubility, as it is found to be poorly soluble in water and is quickly photodegraded under UV radiation <360 nm. However, these obstacles can, in theory, be overcome with the use of direct excitation of the Eu3+ ions at 394 nm and careful design of an analysis instrument to reduce concentration variations.