An efficient down conversion luminescencent probe based on a NaGdF4:Eu3+/Ce3+ nanophosphor for chemical sensing of heavy metal ions (Cd2+, Pb2+ and Cr3+) in waste water

Heavy metal ions (such as Cd2+, Pb2+, Cr3+ etc.) present in wastewater effluents pose a great challenge in developing and underdeveloped countries. Herein, we report a facile hydrothermal synthesis and characterization of hexagonal Eu3+ doped and Eu3+/Ce3+ co-doped NaGdF4 nanophosphors. Importantly, we demonstrate the NaGdF4:Eu3+/Ce3+ nanophosphor as an efficient photoluminescent probe for chemical sensing of heavy metal ions, namely Cd2+, Pb2+ and Cr3+, present mainly in industrial effluents. The structural characterization of the as fabricated nanophosphors has been appropriately performed by powder X-ray diffraction study (PXRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR) and energy-dispersive X-ray spectrometry (EDS). Vibrating sample magnetometry (VSM), photoluminescence (PL) spectra and phosphorescence lifetime measurements of the as synthesized nanophosphors have been used to explore their potential applications. It is observed that Eu3+/Ce3+ codoped nanophosphors show relatively better luminescence intensities as compared to NaGdF4:Eu3+. The energy transfer process (through sensitizer Ce3+ to mediator Gd3+ and finally to activator Eu3+) has been validated in an elegant way. The observed data for chemical sensing of three heavy metal ions (Cd2+, Pb2+ and Cr3+) show good Stern–Volmer fitting.