Preparation And Performance Of Two Kinds Of Cr³⁺-doped Deep-red Luminescent Materials For Plant Growth

The energy required by plants for photosynthesis mainly comes from sunlight,of which blue light,red light and far-red light are particularly important.The utilization rate of solar radiation by crops is low,accounting for only about 0.5%of the total solar radiation,but studies have shown that the utilization rate of solar radiation by crops can exceed 12%.Therefore,improving the utilization rate of light energy by crops is the key to improving production.At present,there are three main ways to achieve plant lighting:1.Traditional light sources such as high-pressure sodium lamps,fluorescent lamps and incandescent lamps;2.LED artificial plant light sources;3.Light-converting agricultural film.Among them,the research of LED plant fill light and luminescent material light-converting agent for light-converting agricultural film has received extensive attention.The currently used light converters have many problems such as low spectral matching,poor thermal stability and high cost.Therefore,this thesis focuses on preparation and luminescent properties of Cr³⁺doped luminescent materials,and the possibility of their application in light converters.The specific research contents and main results are as follows:1.A series of Cr³⁺-doped Sr Mg Al₁₀O₁₇(SAM)red phosphors were successfully synthesized by the traditional high-temperature solid-phase method.The XRD patterns showed that the prepared samples were all good single-phase.Its luminescence properties were tested.It was found that SAM has two strong broad absorption peaks around 400 nm and 540 nm,and emits red light peak at 692 nm,which is attributed to the spin-forbidding of ~2E to ~4A₂ transition of Cr³⁺.The sample with the optimal doping concentration is Sr Mg Al₁₀O₁₇:0.09Cr³⁺,the emission intensity of the sample is the largest.Because of the low luminescence efficiency of Cr³⁺,the SAM sample was mixed up with the Y_2.94Al₅O₁₂:0.06Ce³⁺sample,in order to enhance its absorption around 480 nm to achieve full visible spectrum absorption,thereby enhancing the red light emission of SAM.After the mixed samples were made into a film,the luminescent properties of the light conversion film were tested.It was found that the decrease in the emission light intensity caused by the mixing of different phosphors was suppressed in the light conversion film,and the red light emission intensity of the mixed sample light conversion film is stronger than that of the single SAM light conversion film.Chlorella experiments showed that both light conversion films have the effect of promoting growth.2.The single-phase samples of(Y,Ba)₃(Al,Si)₅O₁₂:Ce³⁺,Cr³⁺were prepared by high temperature solid-state method.The phase purity and morphological characteristics of all samples were analyzed by XRD and SEM.The luminescence properties of the samples were investigated by excitation-emission spectrum,fluorescence decay curve and thermal quenching spectrum.The decay curve analysis results show that there is an efficient energy transfer from Ce³⁺to Cr³⁺in the Y₂Ba Al₄Si O₁₂:Ce³⁺,Cr³⁺samples,and the deep red light at 700 nm is strongly emitted under the excitation of 460 nm blue light.Through monitoring the decay curve of the sensitizer Ce³⁺.Analysis of the data indicated that the mechanism of energy transfer from Ce³⁺to Cr³⁺is dipole-dipole interaction in YBASO matrix.The phosphors has good thermal stability.The sample with the optimal doping concentration is Y_1.97Ba Al_3.9Si O₁₂:0.03Ce³⁺,0.1Cr³⁺,and the external quantum efficiency is 25.7%.Y₂Ba Al₄Si O₁₂:Ce³⁺,Cr³⁺phosphors can absorb visible light at300-650 nm and convert it into deep red light at about 700 nm,and its emission spectrum can match the absorption spectrum of plant photosynthesis.The optimal sample was made into a light conversion film.Then the tomato growth experiment was carried out.The results showed that the light conversion films indeed promoted the stem growth and early fruit ripening of tomatoes.(Y,Ba)₃(Al,Si)₅O₁₂:Ce³⁺,Cr³⁺luminescent materials have the potential to applying in plant growth LED or light conversion films.