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

Abstract

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.