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New Process Preparation And Iron Quenching Research Of Aluminate-based Luminescent Materials

Posted on:2010-01-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:X F YangFull Text:PDF
GTID:1101360272470753Subject:Chemical processes
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SrAl2O4:Eu2+, Dy3+ system long afterglow materials have been accepted as one of the most important luminescent materials, due to the advantages of its wide excitation spectrum, visible emission range, high luminescent intensity, long duration, well chemical stability, no radiation, and environmental capability. These good luminescent properties result in an unexpectedly large field of applications, such as safety exigence, transportation, building and decorating, instruments and apparatuses, electricity, mines, clothing and arts. Currently, the researches focus on improving emission intensity and afterglow time, perfecting long afterglow luminescent mechanism and increasing the red luminescent production.In this paper, the synthesis of ultrafine and high intensity phosphors, quenching research of iron, preperation of Eu2O3 nano rod and its application in SrAl2O4:Eu2+, Dy3+ phosphor, and the synthesis of redγ-LiAlO2:Eu3+ fluorescent were studied and investigated systematically. The results will bring on important significance at the side of improving preparation method, decreasing cost, perfecting recipe formulation and luminescent properties.1. SrAl2O4:Eu2+, Dy3+phosphors with high intensity and none milling were prepared by template-based hydrothermal method using nonionic polyethylene oxide as surfactants. The forming process, structure, morphology and luminescent properties of obtained products were characterized by means of TG-DTG, XRD, TEM, SEM and fluorescence spectrophotometer. The analysis results indicat that the precursor prepared by hydrothermal synthesis method are homogeneously mixed at the molecular level, leading to high reactivity of starting materials and the reduction of sintering temperature, the obtained phosphor powders are consist of uniform small grains and have better luminescence compared with that of solid state method. The critical quenching concentration of Eu2+ of the phosphors prepared by templating synthesis is about 10mol%, which is higher than that of solid state method of 6.6mol%.In this section, the relationship between composition of SrAl2O4:Eu2+, Dy3+ phosphor and its luminescence properities were researched. Through changing the ratio of SrO and Al2O3, the relation between the host phase and persistent luminescence was studied in order to search the changing regularity; the relation between B3HO3 and luminescence properities of product were also studied in order to confirm the optimal doped quantity; the roles of Eu2+ and Dy3+ in SrAl2O4:Eu2+, Dy3+phosphors were studies, and the results suggest that Eu2+ ions are luminescent center, which is the crucial factor, and Dy3+ ions play a role of assistant.2. Because of the cost problem of hydrothermal synthesis method, we explored sol-gel nano-coating method using to prepared SrAl2O4:Eu2+, Dy3+ phosphors. The method has the advantages of esay process, low cost and fitting for large production. In this section, the coasting process has been studied by TEM method, the results insicate that nanometer Al2O3 coat in the surface of SrCO3 and become core-shell precursor. The TG and XRD results prove that reaction temperature is decreased and crystal purity is improved by shintering the core-shell precursor, pure monoclinic phase of SrAlO4 has fomed when the sintering temperature reach to 1000℃, which is lower 300℃than solid state method. The SEM results indicate that the phosphors prepared by sol-gel nano-coating method have the average grain of 3μm. Compared with solid state method, sol-gel nano-coating method can improve the luminescence intensity and long afterglow time of SrAl2O4:Eu2+, Dy3+ phosphors, which expand the application.The research results for the roles of crystal defects in SrAl2O4:Eu2+, Dy3+ phosphors showed that EuSrx is not only luminescent center, but also afterglow center, DySr·can be aselectron trap because of its positive charge which can capture electron, and VSr" can be ashole trap because of its negative charge which can capture hole.3. The luminescence effect on SrAl2O4: Eu2+, Dy3+ phosphors arising from iron impurity was systemically studied in this paper. The results revealed that iron impurity cause quenching for persistent luminescence of SrAl2O4:Eu2+, Dy3+ phosphors, the higher the concentration of the iron is, the lower the persistent luminescence performance is. This can be explained that iron restricts the function of Eu2+ luminescent center and decreases the recombination probability between electrons and holes. The explaination was approved by further exploration, and it was observed that Fe3+ ions is the central factor which cause quenching for persistent luminescence. Aim at above result, it can be put forword that doping Pr3+ or Bi3+ ioins at the preparation of precursor can restrain the quchening effect of Fe3+ ions.4. Eu(OH)3 and Eu2O3 nanorods were synthesized by a facile hydrothermal procedure without template, Eu2O3 nanorods was successfully applied for the preparation of SrAl2O4:Eu2+, Dy3+ phosphors. The results revealed that the obtained Eu(OH)3 nanorods show hexagonal phase and Eu2O3 nanorods show cubic phase. The average size of Eu2O3 nanorods can be calculated of 90nm using Scherrer equation, which agrees with TEM results. Further exploration proved that Eu2+ ions can enter into SrAl2O4 host crystal lattice more easy when use Eu2O3 nanorods as the starting materials, which increase the concentrations of Eu2+ luminescent centre and improve the persistent luminescence of the SrAl2O4:Eu2+, Dy3+ phosphor. 5. A novel Eu3+-dopedγ-LiAlO2 phosphor was successfully prepared by sol-gel nano-coating process. The structure, morphology and luminescence properties of the phosphor were detailed investigated. The results indicate that the obtained products show pure tetragonal phase and narrow size-distribution of about 1.5μm for the particles with sphere-like shape. Luminescence test indicated that theγ-LiAlO2:Eu3+ phosphor emits an intense characteristic luminescence of Eu3+ ions with main peak 612nm, which show red colour. Further experiments proved that feasible concentration of Eu3+, sintering temperature and amount of H3BO3 can useful to improved the luminescence of the phosphor.
Keywords/Search Tags:Long afterglow materials, Strontium aluminate, Template-based hydrothermal method, Sol-gel nano-coating method, Impurity quenching
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