Hydrothermal synthesis, down-/enhanced up-converting, color tuning luminescence, energy transfer and paramagnetic properties of Ln3+ (Ln = Eu/Dy, Yb/Ho)-doped Ba2GdF7 multifunctional nanophosphors

Abstract

A series of down-conversion Ba₂GdF₇:Eu³⁺/Dy³⁺ and up-conversion Ba₂GdF₇:Yb³⁺/Ho³⁺ nanophosphors (NPs) were successfully prepared by a simple one-step hydrothermal method. The structure, morphology, composition, and properties of the multifunctional NPs were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), Fourier-transform infrared (FTIR) spectroscopy, photoluminescence (PL) spectroscopy, and by a vibrating sample magnetometer (VSM). The NPs have a sphere-like morphology and cubic structure. Under ultraviolet excitation, individual Eu³⁺ and Dy³⁺ single-doped Ba₂GdF₇ phosphors exhibited excellent emission in their respective regions. The tunable color tone can be obtained in Eu³⁺ and Dy³⁺ co-doped Ba₂GdF₇ phosphors, and the strong yellow-white and bluish green-white emissions can be seen in Ba₂GdF₇:0.05Eu³⁺,yDy³⁺ and Ba₂GdF₇:0.04Dy³⁺,xEu³⁺ phosphors, respectively. Under 980 nm NIR radiation, intense up-converted visible green emissions were observed in Ba₂GdF₇:0.2Yb³⁺,0.02Ho³⁺ samples. The mechanism of UC emissions was determined to be two-photon absorption. In the Yb³⁺,Ho³⁺ co-doped Ba₂GdF₇ phosphors, the energy transfer processes from Yb³⁺ to Ho³⁺ have been discussed in detail. The enhanced up-conversion luminescence was realized by introducing the sensitizer Yb³⁺ ions to Ho³⁺-doped Ba₂GdF₇ NPs and modifying the cetyltrimethylammonium bromide (CTAB) surfactant on Yb³⁺,Ho³⁺ co-doped Ba₂GdF₇ NPs. Moreover, the as-prepared samples exhibited paramagnetic properties at room temperature. This type of multifunctional nanophosphors have promising applications in light emitting diodes (LEDs), solid state lasers, biolabels, MRI, and so on.