Highly Uniform and Monodisperse beta-NaYF4:Ln~(3+) (Ln = Eu,Tb,Yb/Er,and Yb/Tm) Hexagonal Microprism Crystals:Hydrothermal Synthesis and Luminescent Properties

摘要

beta-NaYF4:Ln~(3+) (Ln = Eu,Tb,Yb/Er,and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route.X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),high-resolution transmission electron microscopy (HRTEM),and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples.It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products.Furthermore,the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE~(3+) (RE represents the total amount of Y~(3+) and the doped rare earth elements such as Eu~(3+) Tb~(3+),Yb~(3+)/Er~(3+),or Yb~(3+)/Tm~(3+)).Under the excitation of 397 nm ultraviolet light,NaYF4:xEu~(3+) (x = 1.5,5%) shows the emission lines of Eu~(3+) corresponding to ~5D_(0-3) ->~7F_J {J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity,resulting in yellow and red down-conversion (DC) light emissions,respectively.When doped with 5% Tb(3+) ions,the strong DC fluorescence corresponding to 5D4 -> 7F_J (J - 6,5,4,3) transitions with ~5D4 -> 7F5 (green emission at 544 nm) being the most prominent group that has been observed.In addition,under 980 nm laser excitation,the Yb(3+)/Er(3+)- and Yb(3+)/Tm(3+)-codoped beta-NaYF4 samples exhibit bright green and whitish blue up-conversion (UC) luminescence,respectively.The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.