Luminescence Spectra And Structures Of Eu²⁺-doped Silicates For White LEDs

China is abundant in rare earth (RE) resources. Because of their same outer-electronconfigurations, so the rare earth loses three electrons in a chemistry reaction easily andbe to the trivalent ions. They are much more lively than metal. There are some other rareearth elements which can be restored after losing electrons, such as Eu、Yb ions. Andsome other rare earth can be further oxidized to tetravalent, such as Tb、Ce ions. Becausethere is a wealth of rare earth elements valence changing, the spectroscopic properties ofrare earth elements are unmatched than general elements. So rare earth is widely applied inluminescence, laser crystals, military, agriculture, and many other hot fields.Silicates are efficient luminescence materials, mainly because of their rigid and verystable crystal structure. So they have to be the efficiency luminescent materials.Rare-earth doped silicates with different crystal structures have been reported forcommercial lighting industry, such as white LEDs. Eu2+has to be as the main activatorions in rare earth luminescence materials due to the luminescence materials with goodstructure and luminescence properties.In this work, the rare-earth doped silicates were chosen to be the host. Theluminescence powder was prepared by high temperature solid-state reaction. Theircomposition and structure were characterized. The samples were checked by XRD andmatch the PDF card, no impurity lines were observed. By analyzing their excitation andemission spectra, discuss the luminescence properties of Eu2+-doped silicates. Make sureluminescence center by analyzing the emission spectra. The possibilities of potentialapplication of the rare-earth doped silicates were studied through the, luminescencedecay curves, color coordinates on temperatures and concentration quenching.In chapter3, the preparation of Ba2CaMg2Si6O17: Eu2+was carried out by solid state reaction method,1.0and10.0mol%Eu2+-doped Ba2CaMg2Si6O17compared with thePDF2card, the main peaks lines well match the standard card. The framework is builtwith layered structure. After discussing with different excitation and emission spectra ofdifferent doping concentrations, it can be effectively excited by UV and presentsblue-emitting luminescence. The luminescence intensity increases with increasing theEu2+-doping concentration. When the concentration is greater than10.0mol%, theluminescence intensity decreased because of conventional concentration quenchingprocess. The lightly Eu2+-doped sample shows one luminescence center for Eu2+on Ba2+,while there are two luminescence centers for Eu2+on both Ba and Ca sites in heavilyEu2+-doped sample. Discussing with the luminescence and temperature curves, theemission intensity decrease about10%when the temperature from25℃to150℃,indicating a weak thermal quenching behaviour. The result show the Ba2CaMg2Si6O17:Eu2+has good thermal stability.In chapter4, the preparation of K4CaSi3O9: Eu2+was carried out by solid statereaction method. The phase formation was confirmed by X-ray powder diffractionmeasurements, the result well match with the PDF2card number39-1427, no impuritylines were observed. When the phosphors was excited by355nm, the Eu2+ions occupymore than on site in the lattice, there are two Eu2+luminescence centers in it, one is530nm and another is586nm. The CIE coordinates were calculated form emissionspectra at different temperatures, it is X=0.319， Y=0.573, it is conventionalyellowish-green-emitting phosphor. The temperature-dependent luminescence spectra ofthe phosphor shows that when the temperature increase form25°C to150°C, theemission intensity is decreased80%of the initial value at25°C which indicating a weakthermal quenching behaviour. The result show the K4CaSi3O9:Eu2+has good thermalstability. With the increasing of temperature, the mission spectra shift from (0.319,0.573)to (0.226,0.514), which is consistent with the blue-shift. This is a shortcoming ofK4CaSi3O9: Eu2+for the application as a LEDs phosphor.In chapter5, Eu2+-activated BaMgSi4O10phosphors, no impurity were observed and all the reflections could be well indexed to the single phase. Discussing the emissionspectra of BaMgSi4O10:Eu2+and BaMgAl10O17:Eu2+. We can found that the luminescenceintensity of BaMgSi4O10:Eu2+is stronger about1.2times than that of BaMgAl10O17:Eu2+.So BaMgSi4O10:Eu2+phosphor exhibits the excellent luminous efficiency. Theluminescence intensity at450K is reduced to87%of the initial value at roomtemperature (300K). It exhibits excellent thermal stability. The layered crystal structurewas reported by many people and presents thermal stability and luminescence efficiency.The novelties of this dissertation are as follows: the phosphor structure, excitedspectra, emission spectra and the potential application of Eu2+-doped silicates（K4CaSi3O9、BaMgSi4O10、Ba2CaMg2Si6O17）were systematical studied. Luminescencedecay curves, color coordinates on temperatures and concentration quenching arediscussed. In summary, it provided a useful potential application with the highluminescence efficiency and thermal stability.