CO32− ion-induced Cu2+ ion determination using DPA capped-LaF3:Eu3+ nanocrystals

Abstract

The fluorescence quenching strategy has been developed as an exceedingly selective and sensitive method for the determination of Cu²⁺ ions in an aqueous medium. For this purpose, we designed and synthesized dipicolinic acid (DPA)-capped-LaF₃:Eu³⁺ nanocrystals (NCs) in water, using microwave irradiation as a heating source. Here, DPA acts as a surfactant, controls the nanocrystal size, and is a sensitizer to Eu³⁺ ions. Upon excitation at 280 nm, DPA transfers its exciting energy to Eu³⁺ ions; subsequently, strong red emission occurs from DPA capped-LaF₃:Eu³⁺ NCs. The intense emission peaks of Eu³⁺ ions are remarkably declined by Cu²⁺ ions accompanied by CO₃²⁻ ions (1 : 6 ratio to Cu²⁺ ions). Cu²⁺ ions with CO₃²⁻ ions in an alkali medium form Cu₂CO₃(OH)₂, a broad and strong absorbent in the UV region, and intersect with the excitation spectra of the DPA-capped LaF₃:Eu³⁺ NCs. More than 90% of the emission intensity of Eu³⁺ ions was quenched after the addition of a 100 μM concentration of Cu²⁺ ions. The quenching was highly selective only towards Cu²⁺ ions and showed almost no interference from many other metal ions. The calculated limit of detection was 117 nM using a linear Stern–Volmer plot.