Microwave-assisted Green Synthetic Approach towards Water Dispersible Luminescent PVP-coated Tb3+ and Ce3+/Tb3+-doped KZnF3 Nanocrystals

Background: Perovskite fluoride nanomaterials are an interesting research topic in material science due to their exciting properties like high-temperature superconductivity, magnetic behaviour, piezoelectric behaviour, etc. Doping of lanthanide ions into the perovskite fluoride nanomaterials makes them more promising as they have applications from biological label-ling to multicolor optical devices. Objective: This study aimed to carry out the synthesis of perovskite KZnF3 nanocrystals in an eco-friendly environment with the help of a microwave-assisted route in a shorter reaction time and at low temperatures. Moreover, it aimed to make the nanocrystals water dispersible, illuminating brighter photoluminescence, which was achieved by coating nanocrystals surface with poly(N-vi-nyl-2-pyrrolidone) and doping of different lanthanide ions (Ln= Tb3+ and Ce3+/Tb3+) respectively, into the KZnF3 nanocrystals matrix. Methods: The synthesis of nanocrystals was performed in an environment-friendly microwave-assisted way and under green conditions. For example, in the preparation of Tb3+(5mol%)-doped KZnF3 nanocrystals, 0.95 mmol of Zn(NO3)2 and 0.05 mmol of Tb(NO3)3 were dissolved in 8 mL of distilled water. Then, an 8 mL aqueous solution of KF (3 mmol) was added to it. The entire mixture was stirred well for 15 minutes. About 60 mg of PVP was added to the mixture and stirred for another 15 minutes. Then, a microwave reaction vessel was made by transferring the final reaction mixture into it and kept under microwave irradiation at 90°C temperature for 15 minutes. Finally, the product was cooled to room temperature and collected by centrifugation. Results: Both Tb3+(5mol%)-doped and Ce3+(15mol%)/Tb3+(5mol%) co-doped KZnF3 nanocrystals exhibit very strong green photoluminescence. The structural and optical properties of as-obtained nanocrystals were characterized by PXRD, field emission scanning electron microscopy, Fourier infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, and photoluminescence spectra. Conclusion: The nanocrystals with uniform cubical morphology having ~60 nm sizes were successfully synthesized. The high photoluminescence efficiency, together with the water dispersibility of the nanocrystals, makes the material useful in many fields of optical devices and offers several biological applications. Moreover, this method could be used to make other lanthanide-doped perovskite fluoride nanocrystals.