Preparation Of Calcium Fluoride Nanomaterial For Greenhouse Film And Fluorescence Enhancement

Facility agriculture is an important part and smybol of modern agriculture.Agricultural greenhouse is not only one of the main mode of facilities agriculture,but also one of the four big projects of agriculture.Light-conversion agricultural film is a controlled agricultural film,which improves the growth environment of crops and promotes the photosynthesis.It not only can keep highly pervious to light and high insulation,but also adjust transmittance and diffuse reflection of incident light on the basis of all kinds of growing plants’nourishment need.Photosynthesis is the basis of plant biomass and yield formation.Researches show that the light with the wavelength from 400 to 480 nm and 600 to 700 nm effectively promote photosynthesis.However,ultraviolet light would reduce plant leaf area,inhibit hypocotyl elongation and even cause plant disease.Yellow light have no contribution to the photosynthesis.Thus,the main purpose of light-convers ion agricultural film is to convert sunlight into the blue and red light in order to promote the photosynthesis.Nano light conversion agent is an optimized auxiliary of light conversion agricultural film.So far,there are serious problems of poor chemical stability,short fluorescence lifetimes and complex synthes is process in light conversion agent.Therefore,this item has great theory significance and utility value for developing chemical stable and good luminous nano light conversion agent.In this paper,Europium doped Calcium fluoride(CaF₂:Eu²⁺)nano light conversion agent was synthesized by coprecipitation method and hydrothermal method.X-ray power diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Field emission scanning electron microscope（FESEM）,High resolution transmission electron microscopy（HRTEM）,Spectrofluorometer,Ultraviolet-Vis ible spectrophotometer（UV-VIS）,Inductively coupled plasma source mass spectrometer（ICP-MS）,Electron paramagnetic resonance（EPR）and fluorescence spectroscopy have been use to analyze the crystal structure,elementary composition,morphology and fluorescence properties.The major research contents include:（1）Europium doped Calcium fluoride(CaF₂:Eu²⁺)nanoparticles have been synthesized by co-precipitation method using different surfactants,in which anhydrous ethanol was used as solvent and the nanoparticles was sintered in air.The luminescent properties of the phosphor were thoroughly examined.Furthermore,the effect of using different surfactants on the sizes of CaF₂:Eu²⁺nanoparticles and related mechanisms were also investigated.The results show that the self-reduction was observed in the as-prepared CaF₂:Eu²⁺nanoparticals and can be explained by charge compensation model based on the substitution.The surfactants affect differently on the particles.The anionic surfactant induces a luminescence quenching phenomenon in CaF₂:Eu²⁺nanoparticles.The nanoparticles with the cationic surfactant have uniform morphology and stable luminescent properties.（2）This section report that plasmon-enhanced fluorescence in Eu²⁺doped CaF₂(CaF₂:Eu²⁺)nanocrystals assembled with citrate-stabilized Ag nanoparticles（Cit-Ag）using a simple hydrothermal method.The effect of Cit-Ag on the sample luminescent properties,quantum efficiency and fluorescence lifetime were studied by fluorescence spectroscopy.The morphology of sample affected by temperature and reaction time were analyzed by SEM and TEM.The mechanisms of plasmon-enhanced fluorescence of CaF₂:Eu²⁺nanocrystals by Ag nanoparicles were also investigated.The results show that,the best conditions were 200^oC,20 h and 200μL Cit-Ag.Silver nanocrystals are ideal building blocks for plasmonic materials that can exhibit a wide range of unique and potentially useful optical phenomena.Surface plasmon enhancement makes significant contribution to enhance the blue fluorescence emission of CaF₂:Eu²⁺.The higher radiative rate and lower nonradiative decay rates result in an increase of quantum yield of the CaF₂:Eu²⁺phosphors.Furthermore,with increas ing Ag concentration,the fluorescence intensity increases to its maximum and then decreases.（3）Europium doped calcium fluoride nanoparticles have been synthesized by hydrothermal method in which Na BH₄ is added as reductant and citrate-stabilized gold（Cit-Au）nanoparticles are used as catalyst,studied on the amount of Cit-Au and NaHB₄,temperature,reaction time,p H value and the size of Au nanoparticles.The mechanisms of catalytic reduction by Ag nanoparicles were also investigated.The presence of small amount of Cit-Au nanoparticles not only catalyze the reduction of Eu ions,but also influence the luminescence intensity of phosphors.It was found that,when the addition of Cit-Au suspension was 250μl and reaction temperature was200^oC,the CaF₂:Eu²⁺phosphors exhibit most intensive and wide emission centered at 423 nm.It also found that the smaller the Au nanoparticles size,the more obvious enhancement effect.In this paper,the research of Europium doped calcium fluoride nanoparticles provides a significant reference for the selection of nano light conversion agent for Light-conversion agricultural film.