Selective Detection of Chromate and Permanganate Ions Using Gallic Acid Capped CaF:Tb Nanocrystals.

In this study, we have developed ligand-sensitized Ln-doped nanocrystals (NCs) for the selective sensing of CrO and MnO ions in nanomolar concentrations. This is accomplished with the gallic acid capped-CaF:Tb NCs. These NCs display bright green emission through an efficient energy transfer from surface functionalized gallic acid molecules to Tb ions upon UV light excitation. The luminescence from Tb ions are selectively quenched by the addition of CrO and MnO 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, PO , SO , VO , WO , IO , ClO ,) had minimal impact on the luminescence intensity of Tb ions. The calculated limit of detection from the experimental results (for the 3σ/slope criterion) is 77 nM and 55 nM for KCrO and KMnO respectively. The findings show that tuning the resonance energy transfer (RET) between analytes and Tb inside the NCs serves as a tool for the detection of dichromate and permanganate ions selectively.