Study On Properties And Applications Of Environment-friendly Luminescent Materials For White LEDs

White LED has the advantages of high efficiency,energy saving,long lifetime,green environmental protection,and simple structure,which is known as the "fourth generation lighting source".As an important component of white LED,fluorescent materials for light color conversion play a vital role in the overall performance of white LED.At present,almost all fluorescent materials are produced by chemical synthesis methods.Although these materials are diversity and color tunability,the complex synthesis process,high cost,environmentally harmful and non-degradable shortcoming limit their practical applications.Natural plant dyes are extracted from the roots,stems,leaves and fruit of plants without chemical processing.They are nontoxic,low cost and environmentally compatible,and have obvious advantages in the field of white LED.This thesis takes pomegranate fruit extract and coptis chinensis extract as research objects,and conducts research on the preparation,spectrum regulation and application of the environmentally-friendly luminescent materials for white LED.The main results are summarized as follows:1.The luminescent properties of pomegranate fruit extract and their applications in white LED were studied.By analyzing UV-Vis,PLE and PL spectra,it was found that pomegranate fruit extract solution can emit strong fluorescence under the excitation of 350-400 nm near-ultraviolet light,and the emission spectrum consists of three visible spectral bands of red,yellow,and blue.The blue color comes from the baicalin and protein components in the extract,while the yellow and red are from the anthocyanin components.The emission intensities of these three colors can be tuned by varying the concentration and excitation wavelength.White light emission with good CIE chromaticity coordinates(0.34,0.33)was obtained from the pomegranate fruit extract solution(12% w/v)at excitation of 350 nm.2.The luminescence properties of berberine(BBR)extracted from coptis chinensis and their applications in white LED were studied.The results show that the untreated BBR is naturally crystalline and emits strong yellow light(540nm)under the excitation of blue light(450 nm).By changing the amount of BBR and working voltage,spectrum regulation of the white LED device was realized.The results show that when the amount of BBR is 0.006 g and working voltage is 2.4 V,the prepared device emits white light with good performance,and the corresponding CIE chromaticity coordinates,CCT and CRI are(0.32,0.33),5934 K and 74,respectively.3.The luminescent properties of BBR-PVA composite thin films and their applications in white LED were studied.The structure and luminescence properties of the composite thin films were studied by XRD,FTIR,PLE and PL spectra.The results show that when BBR concentration increases,the luminescence intensity of the composite film material increases and the peak position is red-shifted,which are caused by the formation of J-aggregates,and then decreases at higher concentration due to the hydrogen bonding between BBR and PVA molecules.The white LED device emits white light with good performance under a film of7-layer and a voltage of 3 V,and the corresponding CIE chromaticity coordinates are(0.3,0.31).