Preparation Of Rare Earth Light Conversion Agents And Their Application In Agricultural Films

The light conversion agents were widely used in the preparation of luminescent materials and the light conversion films. At present, the researches mainly focus on the preparation of rare-earth organic complexes, especially the Eu³⁺ complex. But its emission spectrum doesn't correspond with the absorption spectrum of the plants, and can't provide the blue light which is the essential part of the photosynthesis process. So we are looking for a light conversion material that is cheaper and corresponds with the absorption spectrum of the plants.This article reviewed the researches on rare earth light conversion agents and films. According to the absorption spectrum of the plants, we study the preparation and characterization of rare-earth organic complex containing Sm³⁺ and rare-earth inorganic compounds and their light conversion film. The study is beneficial for obtaining the light conversion agens and films for photosynthesis of plants and improves the modern agriculture. The results show as follows:A new complex Sm_xY_1-x(Sal)₃(phen), in which the Sm³⁺ acts as the light emission center and the Y³⁺ plays the dopant role, is achieved and characterized by IR, UV, fluorescence spectra and thermal analysis. The results show that the dopant of Y³⁺ will strengthen the red light luminescence of samarium and keep the combination between Sm³⁺ and the ligands. The best result was achieved when the dopant amount reaches 90% (mole proportion), furthermore, the main fluorescence emission peak of this series of complexes is at 645 run, which is most closed to the photosynthesis spectrum of plants.The Y₂O₃∶ xEu²⁺ and CaS∶xEu²⁺,yCu⁺ rare earth inorganic light conversion agents which uses (Eu²⁺) as the main emission ion, and (Y³⁺) or (Cu⁺)as the dopant was prepared. And the fluorescence spectra analysis shows that these tow series of agents could convert UV and green light to red light. The Eu²⁺ ion excitates from ⁵D₀ to ⁷F_7/2 thus emits the red light at 611nm.The Eu2+/ Y3+proportion would affect the fluorescence intensity. The bset result was achieved at the ratio of 0.15:0.85. In the CaS inorganic light conversion agents, the Eu2+ doping could convert the green into red light, while Cu+ doping enables abilty of converting light from UV to red or blue. It's interesting when we doped both of them in the material, all the above functions have been achieved. And it has a wide emission peak in the spectrum which means a good absorptance of the sun light for the chlorophyll. The CaS series inorganic light conversion agents has a emission peak at 650nm which is closer to the photosynthesis spectra of plants compared with the Y2O3:xEu2+ one.The inorganic light conversion agents and the organic complexes were mixed into the LDPE plastic to prepare the light conversion films. The results of fluorescence properties of the films show that these light conversion films have a lower transmittance in the UV-VIS spectrum than the ordinary films. The transmittance in visible light spectrum reduced to 90%, and the absorption peak is found in the ultraviolet spectrum. In the fluorescence spectrum, no excitation peak was found in ultraviolet or emission peak in red wave band. The light conversion effect of ultraviolet to red was found in the Y2O3:xEu2+(Eu:Y=0.15:0.85mol) films series. And no light conversion phenomenon is found on any other films, which is possibly caused by these light conversion agents with large particle size or being incompatible with the PE films. More research should be investigated thouroughly.