[Color-tunable nano-material alpha-NaYF4 : Yb, Er, Tm prepared by microemulsion-hydrothermal method].

NaYF4:Yb 3+,Er 3+,Tm 3+ nanoparticles were prepared by microemulsion-hydrothermal method.Crystal phase,morphology and structure of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) .The luminescence properties were studied by up-conversional fluorescence spectroscopy.The XRD patterns of as-prepared samples were in agreement with the PDF#77-2042of cubic NaYF 4 .SEM images of the particles showed that the samples were cotton-like spherical in shape and which were assembled by smaller nano-particles.The average size was 120nm,while the shape was regular and the particle size was homogeneous.Under the excitation of 980nm,the as-prepared particles could emit blue (438and 486nm), green (523and 539nm) and red (650nm) light simultaneously.It can be seen from the color coordinates figure (CIE) that when doping concentration ratio of Tm 3+ and Er 3+ increased from 0to 2,the whole emitting light color of samples movedto green region.While the ratio was 1:1,pseudo white light was obtained.As the ratio changed from 2to 7,the luminous color was moved to red region.