A High‐Efficiency and Low‐Cost Luminescent Sensor for Rapid Cu 2+ Detection

In this work, a simple, low‐cost, rapid, and highly selective method for the detection of Cu 2+ is developed using luminescence core–shell structure Gd 2 O 3 :Eu 3+ @SiO 2 composites. The sample has been characterized by X‐ray diffraction, transmission electron microscopy, and photoluminescence. Systematic luminescence studies demonstrate that Gd 2 O 3 :Eu 3+ @SiO 2 exhibits a high quenching efficiency for Cu 2+ detection through the inner filter effect. Additionally, the fluorescence intensity of Gd 2 O 3 :Eu 3+ @SiO 2 decreases with the increasing concentration of Cu 2+ , and the low detection limit is 9.7 × 10 −5  M −1 . The sensing system is successfully applied to the detection of Cu 2+ in human urine samples, showing high recyclability. Furthermore, the fluorescence quenching mechanism of the Gd 2 O 3 :Eu 3+ @SiO 2 /Cu 2+ mixture is investigated in depth.