| Because white light emitting diode has the advantages of high efficiency, long lifetime, fast response, safety and environmental protection, it has attracted more and more attention. Recently phosphor-converted (pc) method is the most common to fabricate white LED. As the important ingredient in pc-white LED, phosphor affects the development and application of white LED directly. Because of limitation of red phosphors applied nowadays, especially to the properties of red phosphor exeited by blue and UV light, which can affect directly the color rendering of white LED. In addition, the commerical phosphors are generally prepared by conventional high temperature solid state reaction which gradually cannot meet the demand of development in the area of light and display, because of energy-consuming and uncontrollable for the shape of partieles etc. Therefore, it is great meaningful to develop new good properties of red-emitting phosphors and propose a novel effective way for the preparation of phophors.With molybdates as host materials, a series of red-emitting materials co-doped with Eu3+, Sm3+, Tb3+, Y3+, La3+and Gd3+were synthesized by hydrothermal synthesis method. The energy transfer pathway in rare earth ions was studied, and their luminescent properties were improved by charge compensation. Through XRD, scanning electron microscopy, excitation spectra and emission spectra analysis etc, the influences of technological condition, co-doping, charge compensation and so on the luminescent characteristics of luminescent materials were investigated. The main work and research results are as follows:Eu3+activated M0.92MoO4:Eu0.083+(M=Ca, Sr, Ba) and CaxSr1-x-1.5yMoO4:Euy3+red-emitting materials were prepared by hydrothermal synthesis method and the effects of technological conditions on materials structure and luminescent intensity were investigated. The results are as follows:Firstly, For the red-emitting materials M0.92MoO4:Eu0.083+(M=Ca, Sr, Ba) and Ca0.70Sr0.18MoO4:Eu0.083+with hydrothermal method, the particle size is small, and the particle size distribution is uniform, and morphology has got a good improvement in comparison with those of materials prepared by solid-state method.Secondly, when the introduction of Eu3+into MMoO4(M=Ca, Sr, Ba), the order of luminescent intensity from strong to the weak is Ca0.92MoO4:Eu0.08+>Sro.92MoO4:Eu0.083+>Ba0.92MoO4:Eu0.083+.Thirdly, when Eu3+concentration and Ca2+concentration are8%and70%, respectively, and hydrothermal reaction condition is at180℃for12h, the luminescent intensity(616nm) of CaxSr1-x-1.5yMoO4:Euy3+prepared at900℃for2h is the best.Fourthly, M0.92MoO4:Eu0.083+(M=Ca, Sr, Ba) and Ca0.70Sr0.18MoO4:Eu0.083+can be effectively excited by395nm and465nm wavelength light, which can match ultra-violet and blue chips in light-emitting diodes application. Their chromaticity coordinates is closer to the standard red than that of Y2O3:Eu3+, and conforms to the standard requirements of our country color TV phosphors (SJ1536-79), and is closer to the standard values of International chromaticity coordinates. So those red-emitting materials show good potential of the red commercialization phosphors.By hydrothermal synthesis method, Eu3+-Sm3+, Eu3+-Tb3+, Eu3+-Y3+, Eu3+-La3+and Eu+-Gd+co-doping luminescent materials were prepared and the influences of Eu+, Re3+(Re3+=Sm3+, Tb3+, Y3+, La3+and Gd3+) on luminescent intensity of luminescent materials were investigated. The results are as follows:Firstly, via hydrothermal synthesis method, the morphology of five kinds of luminescent materials has got a good improvement, and the particle size is small, and the particle size distribution is uniform.Secondly, when co-doping ions are introduced, the host lattices of red emitting luminescent materials cannot be changed. Five optimum luminescent materials are obtained, such as Ca0.70Sr0.135MoO4:Eu0.083+,Sm0.033+、Ca0.70Sr0.12MoO4:Eu0.083+, Tb0.043+、 Ca0.70Sr0.09MoO4:Eu0.083+, Y0.063+、Ca0.70Sr0.12MoO4:Eu0.083+, La0.043+and Eu0.083+,Gd0.033+■Thirdly, the occurrence of energy transfer in co-doping ions was studied. The energy transfer pathway from Sm3+to Eu3+is from4G5/2of Sm3+to5Do of Eu3+and the energy transfer pathway from Td3+to Eu3+is from5D4of Td3+to5D0of Eu3+.Fourthly, the five optimum luminescent materials can be effectively excited by395nm and465nm light, the main emission peak lie616nm. Their chromaticity coordinates is closer to the standard red than that of Y2O3:Eu3+, and conforms to the standard requirements of our country color TV phosphors (SJ1536-79), and is closer to the standard values of International chromaticity coordinates. So those red-emitting materials show good potential of the red commercialization phosphors.With alkali carbonates as charge compensators, the improvement of luminescent properties was studied and a good result had got. The results are as follows: Firstly, to Ca0.70Sr0.22MoO4:Eu0.083+, the charge compensating model is2Ca+/Sr2+-> Eu3++Li+/Na+/K+with Li2CO3, Na2CO3and K2CO3as charge compensators. When the molar concentrations of the charge compensators are6%Li+、8%Na+and4%K+, respectively, luminescent intensity and chromaticity coordinates of the red-emitting materials Ca0.70Sr0.22MoO4:Eu0.083+correspond to1918a.u.、x=0.65、y=0.33,2045a.u、 x=0.67、y=0.33and1711a.u.、x=0.66、y=0.32. Their emission intensity can be improved to41%,50%and26%, respectively. The optimized charge compensator is Na+.Secondly, the charge compensating model is2Ca2+/Sr2+-> Eu3+/Re3++Na+(Re=Sm、 Tb、Y、La%Gd) with Na2CO3as charge compensator. When the molar concentrations of Na+are0.06,0.08,0.10,0.10and0.08in turn, the luminescent intensity of the five luminescent materials can be improved to59%,40%,55%,47%and56%orderly. Their chromaticity coordinates is closer to the standard values of International chromaticity coordinates.The innovations of this paper are as follows:Firstly, the ideal structure and the luminescent properties of luminescence materials were prepared successfully by hydrothermal synthesis method, which provided another kind of energy-saving and effective way for the synthesis of luminescence materials.Secondly, the effect of co-activators on emission properties of luminescent materials and the occurrence of energy transfer in co-doping ions were studied. The energy transfer pathway from Sm3+to Eu3+is from4Gs/2of Sm3+to5D0of Eu3+and the energy transfer pathway from Tb3+to Eu3+is from5D4of Tb3+to5D0of Eu3+, which provide references for improving luminescence properties of currently existing phosphors and developing new luminescence materials.Thirdly, studying initially the charge defect by doping Sr/Ca in the molybdates and the luminescent properties are optimized by different charge compensators to seek one ideal high-efficient luminescent material.Fourthly, the chromaticity coordinates of red-emitting materials are closer to the standard red than that of Y2O3:Eu+, and conforms to the standard requirements of our country color TV phosphors (SJ1536-79), and is closer to the standard values of International chromaticity coordinates. So those red-emitting materials show good potential of the red commercialization phosphors. |
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