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

Abstract

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, BaGd_0.78−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.