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