3,5-Dihydroxy Benzoic Acid-Capped CaF:Tb Nanocrystals as Luminescent Probes for the WO Ion in Aqueous Solution.

We report a facile and effective luminescence method for the determination of the WO ion in aqueous medium at initial pH = 6.3. This is achieved using 3,5-dihydroxybenzoic acid-capped CaF:Tb (5%) nanocrystals (NCs) as a luminescent probe. This is accomplished based on the energy transfer luminescence from the WO ion to the Tb ion in small-size CaF:Tb NCs. Hydroxyl groups on the surface ligand helps in binding the tungstate ion to the surface of the NCs. With the gradual addition of the WO ion, the intensity of the Tb excitation and emission spectra significantly increased. The linear range of the detection was from 1 to 10 μM for the WO ion ( = 0.99). The calculated detection limit was 0.4 μM (by applying the 3σ/K criterion).