Tunable multicolor upconversion luminescence and paramagnetic property of the lanthanide doped fluorescent/magnetic bi-function NaYbF_4 microtubes

摘要

In this paper, the lanthanide (Ln) doped fluorescent/magnetic NaYbF_4 microtubes with hexagonal phase were synthesized via a hydrothermal method using oleic acid as a capping ligand and surface modifier. The as-prepared samples were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), upconversion luminescence (UCL) spectra, and vibrating sample magnetometer (VSM). The TEM and FE-SEM observations revealed that the NaYbF_4 microtubes present high quality hexagonal prism shape. Under the excitation of a 980 nm laser diode (LD) with a power density of 0.5 W cm~(-2), the UCL colors can be tuned from purplish blue to blue, greenish white, and further to yellowish green by adjusting the Tm~(3+) and Ho~(3+) content in NaYbF_4 system. Moreover, the brighter greenish white light can be readily achieved via increasing excitation power. The UCL mechanisms for the white emission were proposed based on the spectral and pumping power dependence analyses. Moreover, these as-prepared NaYbF_4 microtubes exhibit excellent paramagnetic property at room temperature. The magnetic mass susceptibility and magnetization are measured to 4.17 x 10~(-5) emu/gOe and ~0.84 emu g~(-1) at 20 kOe, respectively. Therefore, these NaYbF_4 microtubes with hexagonal prism shape, tunable multicolor UCL and excellent paramagnetic property imply that NaYbF_4 is an excellent host material and may find applications in flat-panel displays, lasers photonics and dual-modal bioprobes.