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The Preparation And Properties Research Of Rare Earth Doped Luminescent Materials

Posted on:2016-09-28Degree:MasterType:Thesis
Country:ChinaCandidate:P LiuFull Text:PDF
GTID:2311330479452582Subject:Radio Physics
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Ln3+(lanthanide)-doped inorganic materials posess high chemical, thermal and environmental stability, low toxicity, reduced photobleaching. Due to the adequate 4f electronic shells, they also exhibit special PL including efficient emissions from the ultraviolet(UV), passing through the whole visible, to the mid-infrared light region with a sharp emission spectrum and a long lifetime. Enlightened by the above advantages, they are considerated promising phosphors for a wealth of applications in the fields of lasers,displays, sensors, solar cells, electroluminescent devices, and biomedical research.Concentrating on the current hot topics and problems to be solved in real application, we conducted many relatedexploratory investigations as the following four aspect in this context :1) new approaches for the fabrication of required inorganic materialsWith the development of modern science and technology, the requirements of crystal materials are improved. For nanoparticles, products with well-defined surface morphology,uniform dimensions and shape, special structure such as core-shell structure has been widely explored. And for some qualified single crystal applied in hi-tech device, products synthesized by convential method cannot reach the need or even beyond of fabrication.We adopted a convenient and efficient hydrothermal method to produce amouts of microparticles with ideal surface morphology and hollow-core spherical structure. Besides,a series of qualified Ln3+-Y/Gd VO4 single crystal were successfully grown with the help of optical floating zone method. We also investigated the growth process and summarised some experiences for future groeth.2) basic research on the photoluminescence(PL) properties of Ln3+ionsA series of Eu3+/Er3+-(Y/Gd)(V/P)O4 materials were prepared with differentmorphology including bulk, nano/micro-particles and single crystal. Considering the complexity of crystal growth, it is very important to establish the relationship between the observed complex phenomena with the underlying fundamental theories, which has an essential value to extend for both controllable synthesis and practical application.Comparing the spectra of different samples, we found that the particle size, surface defects,host, excitation wavelength and doping concentration play an significant role in the final PL including position, intensity, breadth of emission peak. For Er3+doping case, the green emssion at 554 nm is highly promoted with the reduction of inner and surface defects in nano/micro-particles comprared to bulk. And the Er3+ doping single crystasl even exhibit high near-infrared(1550 nm) emission. As for Eu3+ case, the 5D0?7F2,4 emissions vary with the change of crstal structure. A relevant PL dynamic mechanism was proposed.3) improving the PL efficiency with co-doping ionsThe poor absorption due to the forbidden f-f transition of Ln3+ions is the major limits for the efficiency improvement. The Ce3+ and Bi3+ ions are proved to be excellent sensitizer for several Ln3+ons with not only enhancing the emission intensity. In our case,Bi3+and Ce3+are suitable sensitizer for Eu3+for the efficient Bi3+/Ce3+?Eu3+energy trasfer,which also occur in Bi3+?Sm3+, Ce3+?Er3+ and Ce3+/Eu3+?Yb3+ combinations. While in Bi3+?Dy3+/Er3+ couples, because of the energy back trasfer from Dy3+/Er3+ to Bi3+ and the emssion of Bi3+ ion itself, the sensitization process is very weak. In Ho3+-Yb3+ couple,down-conversion(DC) and up-conversion(UC) luminescence were detected with the different intensity ratio of green emission to red emission. Spectral conversion with DC and UC is most beneficial for solar cells, commercial lighting and display devices.4) PL of Eu3+and Er3+under high magnetic fieldComparing to these studies dealing with splitting and shift of spectroscopic lines in magnetic field, the investigations concerning its effect on the integral intensity of the transition lines has not yet been widely addressed. We then study the the effect ofmagnetic field on the integral intensity of YVO4:Er3+ and Y/Gd VO4:Eu3+ single crystal in detail. We found that the green emission(554 nm) intensity of Er3+ is suppressed by applying magnetic field up to 50 T. We argue that this effect arises from different Judd–Ofelt intensities of transitions for the two Kramers doublets of the emitting 4S3/2multiplet cause by off-center displacement of Er3+ions. While In the YVO4:Eu3+single crystal, the electric dipole transition of Eu3+ 5D0?7F2,4 decreases and the blue and red shift occur with the presence of the magnetic field. While in the Gd VO4:Eu3+courterpart, the5D0?7F2,4 emssion show a strong improvement. We assumed the difference originate from the structural change of symmetry of Eu3+ ions in single crystals induced by high magnetic field.
Keywords/Search Tags:lanthanide, optical floating zone method, up/down conversion, PL efficiency improvement, co-doping combination, high magnetic field, integral intensity
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