First-principle Study On Rare Earth Doped Fluoride Upconversion Material And Its Preparation

Rare earth (RE3+) doped up-conversion luminescent material can convert the infraredlight that can’t be absorbed by silicon solar cell into the visible light that can be absorbed,thus increasing the absorption and utilization of solar spectrum. The matrix and rare earthions both have important impacts on luminescence property in RE3+doped up-conversionmaterial. In this paper, we use the first-principle theory to study properties of differentmatrices and different rare earth ions doped NaYF4, and use the hydrothermal approach tosynthesis NaYF4:Er/Yb, then study how the reaction time, temperature and pH impact thesamples’phase and morphology. After determining the optimum parameters, wesynthesis NaYF4:Ho/Yb, NaYF4:Er/Yb and NaYF4:Tm/Yb, then study the luminescentproperty of each sample.Through the first principle study of three different mitrices: β-NaYF4, β-NaYbF4andβ-NaLuF4, we find that the stability of β-NaLuF4is higher than the other two systems. Theabsorption and reflectance in the infrared light region of β-NaYF4are both the lowest,which is propitious to reduce the loss of the excitation light.Through the first principle study of five different RE: Dy, Ho, Er, Tm, Yb dopedNaYF4systems, we find that after doping, the cell volume of NaYF4has slightly reduced.RE doped systems only have faint absorption in infrared light except Yb, which is thereason why most RE single doped upconversion materials have a low upconversionefficiency.Yb doped system has the strongest reflectance in infrared light, and Er dopedsystem has the lowest reflectance in infrared light.By hydrothermal approach, we synthesis NaYF4:Er/Yb under different processparameters, and find that long reaction time and acid condition are helpful to thegeneration of β-NaYF4. The phase of sample gradually changes from α-NaYF4to β-NaYF4as the reaction temperature increases, and when temperature further increases, the samplephase doesn’t change, but the crystal defects will increase and the particle dispersion willbecome poor. Then we synthesis NaYF4:Ho/Yb, NaYF4:Er/Yb and NaYF4:Tm/Yb under180℃, pH=3and24hours. The samples are all pure β-NaYF4and the crystallines are all perfect. Upconversion luminescence phenomenon is observed in all of the three samples,and NaYF4:Tm/Yb has a very strong emission peak at800nm, which is just in thewavelength that silicon solar cell absorbs most.