Selective Detection of Chromate and Permanganate Ions Using Gallic Acid Capped CaF₂:Tb³⁺ Nanocrystals

Abstract

In this study, we have developed ligand‐sensitized Ln3+‐doped nanocrystals (NCs) for the selective sensing of Cr2O72− and MnO4− ions in nanomolar concentrations. This is accomplished with the gallic acid capped‐CaF2:Tb3+ NCs. These NCs display bright green emission through an efficient energy transfer from surface functionalized gallic acid molecules to Tb3+ ions upon UV light excitation. The luminescence emissions from Tb3+ ions are selectively quenched by the addition of Cr2O72− and MnO4− anions. The reduction in the luminescence intensity is found to be quite selective, as the addition of other strong oxidizing species (I−, F−, Br−, Cl−, PO32−, SO42−, VO3−, WO42−, IO3−, ClO4−,) had minimal impact on the luminescence intensity of Tb3+ ions. The calculated limit of detection from the experimental results (for the 3/slope criterion) is 77 nM and 55 nM for K2Cr2O7 and KMnO4, respectively. The findings show that tuning the resonance energy transfer (RET) between analytes and Tb3+ inside the NCs serves as a tool for the detection of dichromate and permanganate ions selectively.