Hydrothermal Synthesis And Regulation Of Rare Earth Doped Alkaline Fluoride Micro / Nano - Luminescent Materials

Recent years, rare-earth doped luminescent micro/nano-materials have been widely used in luminescence, display, biological labeling and imaging, catalysis, drug delivery, energy sources, and so on due to their unique optical, electrical and chemical properties. The luminescent properties of phosphor is closely related to the crystal morphology, size and dimension, so it is important to control the morphology, size, and the process of crystal growth for micro/nano-materials using a simple method. Here, the alkaline earth metal fluorides MF2(M=Ca, Sr, Ba) micro/nano-meter luminescent materials doped with Tb3+/Ho3+-Yb3+ ion pairs have been synthesized by using a simple hydrothermal method. Moreover, the up/down-conversion properties and the energy transfer mechanism of samples have also been discussed in detail.With the addition of different chelating agent and fluoride source in the process of synthesis by hydrothermal method, the CaF2 micro/nano-particles with diamond-like and cubic shape were obtained. The formation mechanisms of different morphologies were also analyzed. CaF2:Tb3+/Yb3+ and CaF2:Ho3+/Yb3+ particles with cubic morphologies were prepared, and their photoluminescence, mechanism of the up/down-conversion have also been investigated.The BaF2 micro-crystalline particles with rubik-cube structure morphology were first prepared with citric acid as a chelating agent. The factors that affected the morphology and particle size of samples, including the chelating reagents, pH value and reaction times, were investigated. It is found that the un-doped BaF2 samples display a strange blue emission under the excitation of 336nm, in which the mechanism of the blue emission has also been discussed. The Tb3+/Ho3+-Yb3+ pairs co-doped BaF2 nanophosphors were also synthesized by hydrothermal method, and the luminescent properties and decay times of the samples were investigated, respectively.Highly uniform SrF2 micro-spheres assembled by SrF2 nano-structural units in the presence of citric acid were also obtained by hydrothermal method. Results indicate that reaction time and chelating reagent play a key role in forming the microspheres. The formation mechanism was proposed based on the evolution of this morphology as a function of reaction time. Meanwhile, the up and down conversion luminescence of lanthanide ions (Tb3+, Ho3+, and Yb3+) doped SrF2 nano-materials were investigated. Under excitation at 980 nm, the SrF2:Tb3+/Yb3+ sample exhibits a strong green emission centered at 543 nm from 5D4â†'7F5 transition of Tb3+ while the SrF2:Ho3+/Yb3+ also exhibits green emission at 543 nm from 5S2,5F4â†'5I8 transition of Ho3+. In contrast, the near-infrared emission involving Yb3+ 950-1100nm (2F5/2â†'2F7/2) was achieved in samples SrF2:Tb3+/Yb3+.and SrF2:Ho3+/Yb3+ nano-materials. The possible near-infrared down conversion mechanism was proposed, and lifetime measurements were also carried out to support our proposal.