Dual-mode, tunable color, enhanced upconversion luminescence and magnetism of multifunctional BaGdF5:Ln3+ (Ln = Yb/Er/Eu) nanophosphors

A series of Yb3+, Er3+, and Eu3+ ions doped BaGdF5 dual-mode (down-conversion (DC) and upconversion (UC)) luminescent nanophosphors were successfully prepared by a simple one-step hydrothermal method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrometry (EDS), Fourier-transform infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy, fluorescence lifetime measurements, and vibrating sample magnetometry (VSM) were utilized to characterize the samples. Under 274 nm UV light excitation, BaGd0.78−zF5:0.2Yb3+,0.02Er3+,zEu3+ phosphors emitted orange emission. Under 980 nm NIR irradiation, intense up-converted visible green emissions were observed in BaGdF5:Yb3+,Er3+/Eu3+ samples. The mechanism of UC emissions involved two-photon absorption. In the Yb3+,Er3+,Eu3+ co-doped BaGdF5 phosphors, the energy transfer processes from Gd3+ to Eu3+ and from Yb3+ to Er3+ were discussed. Tunable colors were visualised with the help of the Commission Internationale de L'Eclairage (CIE) chromaticity diagram and the processes responsible for the DC and UC emissions were discussed in detail. The enhanced up-conversion luminescence of Yb3+,Er3+/Eu3+ co-doped BaGdF5 nanophosphors (NPs) was realized by modifying the trisodium citrate (Cit3−) surfactant. Moreover, the as-prepared samples exhibited paramagnetic properties at room temperature. This type of multifunctional orange-green emitting nanophosphor has promising applications in solid state lasers, lighting, MRI, anti-counterfeiting, biolabels, and so on.