Controllable Synthesis And Up-conversion Luminescence Properties Of Ba-Cl-F And Ba-Yb-F Nanocrystals

Due to its unique up-conversion performance, such as excellent photostability, nonblinking, no autofluorescence, deep penetration depth, multicolor emission, rare-earth doped up-conversion nano-particles（UCNPs） are used in many fields, especially the enormous application in the field of biological imaging. It has important academic value and practical significance to satisfy the demands of biological imaging by choosing appropriate rare earth doped host materials and realizing its controllable synthesis. Alkaline earth-rare earth fluoride and alkaline earth fluoride chloride are ideal up-conversion host materials because of its lower phonon energy and good chemical stability. As we all know, the crystal phase, size and morphology have a great impact on nanocrystals performance. So it is necessary to realized the controllable synthesis of alkaline earth-rare earth and fluoride-chloride, research the laws of crystal phase, morphology, size variation, in order to get the size-, shape-controlled nanocrystas with good up-conversion performance. Therefore, the main research contents and conclusions in this article are as follows:1. Controllable synthesis and up-conversion luminescence properties of Ba-Cl-F nanocrystal.Using solvothermal method, by adjusting the molar ratio of F-/Ba²⁺ from 1:1, 2:1, 3:1 to 4:1, the product confirmed as tetragonal BaFCl, pure hexagonal phase Ba₇F₁₂Cl₂, pure hexagonal phase Ba₇F₁₂Cl₂, the mixture of hexagonal Ba₇F₁₂Cl₂ and BaF₂, respectively. The length of hexagonal Ba₇F₁₂Cl₂ nanorod increased and diameter decreased with the molar ratio of F-/Ba²⁺ increased, and the size uniformity is deteriorated; Gradually raising the reaction temperature from room temperature to 200℃, phase transition from tetragonal BaFCl to the hexagonal phase Ba₇F₁₂Cl₂ was founded. Prolong the reaction time from 3h to 12 h, tetragonal BaFCl chloridized from cubic Ba F₂ at first, after that, tetragonal BaFCl fluoridize as hexagonal phase Ba₇F₁₂Cl₂; By increasing the amount of NaOH, it is in favor of the phase transition from tetragonal Ba FCl to hexagonal Ba₇F₁₂Cl₂, and weakened the anisotropic growth of hexagonal phase Ba₇F₁₂Cl₂, size uniformity improved. The size of pure BaFCl:Yb³⁺, Er³⁺ nanocrystals first increases then decreases, and the intensity of green up-conversion emission band was gradually reduced with the rising doping concentration of Yb³⁺; Increase the Yb³⁺ doping concentration, Ba₇F₁₂Cl₂:Yb³⁺, Er³⁺ nanocrystals with increased percentage of Ba FCl, and the intensity of green emission band increased, the red emission band decreased.2. Controllable synthesis and up-conversion luminescence properties of Ba-Yb-F nanocrystal. Using a solvothermal method, when added 0.6g NaOH, products crystal phase include hexagonal phase NaYbF₄, cubic Na5Yb9F32, new monoclinic phase with nominal composition of BaxYb1-xF3-x（0.2≤x≤0.5）, and the cubic phase BaYbF₅, cubic BaF₂; When without adding NaOH, Ba-Yb-F crystal phase include YbOF, monoclinic BaYb₂F₈, cubic phase BaYbF₅ and the cubic BaF₂; In the situation of adding 0.6gNaOH into the reaction system, pure monoclinic phase region with nominal composition BaxYb1-xF3-x（0.2≤x≤0.5）, its nanosheets size varies with the change of the amount of Yb³⁺. In the pure cubic phase BaYbF₅（0.65≤x≤0.8） area, the phase morphology change with the variation of Yb³⁺ concentration; Na⁺ proved induced the formation of new monoclinic phase BaxYb1-xF3-x（0.2≤x≤0.5）; Multicolor emission can be achieved by doping Er³⁺ into monoclinic phase BaxYb1-xF3-x（0.2≤x≤0.5）, the emission color across from red to yellow, to green; Multicolour upconversion of BaYb₂F₈: Er³⁺/Tm³⁺ also obtained.3. The synthesis and up-conversion luminescence properties of Mn²⁺ doped BaYbF₅:Er nanocrystals. The crystal phase of pure BaYbF₅:Er could be prepared when incerease Mn²⁺ doping concentration as high as 40mmol%; And the up-conversion intersity decreased when gradually increase the concentration of Mn²⁺, so does the crystal size.