Selective detection of iron (III) using salicylic acid capped Tb3+-doped CaF2 colloidal nanoparticles

Lanthanide (Ln3+) doped nanoparticles (NPs) possess sharp luminescence peaks with long excited state lifetimes. In this manuscript we have utilized these features for the selective detection of Fe3+ ions through resonance energy transfer approach. This is achieved using salicylic acid (SA) capped Tb3+-doped CaF2 (SA@CaF2:Tb3+) NPs. These nanoparticles exhibit bright green color emission upon ultraviolet (U.V.) excitation due to the strong energy transfer from the salicylic acid molecules to Tb3+ ions. An enhancement in the green emission intensity close to 40 times is noted. Upon addition of ferric ions, the emission intensity of the green emission is greatly reduced. The spectral overlap of the SA emission with the absorption of the analyte is assumed to be the reason for the selective quenching of the luminescence intensity. As a consequence, the overall energy transfer efficiency from salicylic acid to terbium ions (Tb3+) is reduced resulting in the lowering of Tb3+ emission intensity. The calculated detection limit for the ferric ions is 8.7 μM. The selective decrease in the green emission intensity upon Fe3+ is confirmed by the introduction of other cations like Ni2+, Mn2+, Cu2+, Co2+, Cr2+, Pb2+, Zn2+ and Mg2+ resulting hardly in any alteration to the Tb3+ emission intensity. This work clearly directs that the resonance energy transfer (RET) using Tb3+-doped NPs can be used as a technique to detect ferric ions. [Display omitted] •Salicylic acid is used as a multifunctional ligand like capping agent, sensitizer and linker.•Efficient energy transfer from salicylic acid to Tb3+ ions in SA@CaF2:Tb3+ resulted in intense green emission.•Salicylic acid capped CaF2:Tb3+ nanoparticles is used as an optical probe for the selective detection of Fe3+ ions.