Green emitting CaMoO$_4$:Tb$^{3+}$ nanoparticles as luminescent probe for selective sensing of Fe$^{3+}$/Fe$^{2+}$ ions

Abstract

Polyvinylpyrrolidone (PVP) functionalized Tb$^{3+}$ activated CaMoO$_4$ nanoparticles (NPs) were prepared through hydrothermal synthesis method. The structure and morphology of the tetragonal phase CaMoO$_4$ nanoparticles were characterized using XRD and TEM respectively. The surface functionalization and formation of the sample was confirmed from the FT-IR spectroscopy. The photoluminescence (PL) studies show the presence of broad absorption peak $\sim$275 nm corresponds to the MoO$_4^{2-}$. An intense green emission of Tb$^{3+}$ at 544 nm was observed. This is due to efficient energy transfer from host to the activator i.e. from the molybdate absorption to the excited states of Tb$^{3+}$. Out of various metal ions, the nanoparticles show selective detection of Fe$^{3+}$ ions in the whole pH range with a limit of detection of $\sim$6 $\mu$M. Also, these nanoparticles detect Fe$^{2+}$ ions in alkaline media. This is due to PL quenching of the NPs in the presence of Fe$^{3+}$/Fe$^{2+}$ ions. Both dynamic and static quenching are responsible for PL quenching process. The PL decay lifetime also supports the nature of quenching mechanism. These NPs could be a potential candidate for sensing of Fe$^{3+}$/Fe$^{2+}$ ions in aqueous media.