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Study On The Structure And Luminescence Properties Of BCNO Phosphor

Posted on:2014-04-08Degree:MasterType:Thesis
Country:ChinaCandidate:F LuFull Text:PDF
GTID:2251330422965993Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
In this thesis, BCNO phosphors were prepared based on the reaction of urea, boric acid andpolyethylene glycol by a low-temperature liquid-phase method. Through changing the rawmeterials and their moral ratios, the synthetic temperatures and sintering time periods, weconfirmed the best synthetic method of these BCNO phosphors as follows: polyethylene glycols(PEGs)(Mw=20000), boric acid and urea were used as the carbon, boron and nitrogen sourcesrespectively, and the molar ratio of C/B and N/B was0.002and5respectively (the molarquantity of boric acid was fixed at0.02mol), and the sintering temperature and heating time was750℃and45min respectively. Then we adopted the annealing method and investigated theinfluences of annealing on the structure and luminescence properties by changing the annealingambiences, temperatures and time periods. Subsequently, we illustrated the internalluminescence mechanisms.In the high-temperature annealing experiments, the annealing temperature range is800-1400℃, and the annealing ambiences are argon, nitrogen, mixture of hydrogen and argon (5%H2+95%Ar), and ammonia, respectively. When the as-prepared samples were annealed undervarious ambiences, the crystallinity quanlity is improved and the excitation and emission peakswere blue-shifted and splitted into new PL (photoluminescence) peaks. The excitation peakswere blue-shifted from280nm and370nm to270nm and310nm, and the emission peaks wereblue-shifted to the two regions of300-350nm and400-450nm. In addition, the change rate ofPL peaks was higher when the samples were annealed under ammonia and mixture of hydrogenand argon ambiences than under other ambiences. High-temperature annealing experimentsindicated that the peak shift was induced by the bandgap change including changes of crystalstructure, chemical composition, the ratio of B-O to B-N and atomic bonds of BCNO phosphor.In the low-temperature annealing experiments, when samples were annealed under differentambiences, both the annealing temperature and time were different. When samples wereannealed under nitrogen for short time periods, the emission intensity decreased sharply. But when the annealing time period increased to4hours, the emission peaks were blue-shifted. Theemission peaks were red-shifted when samples were annealed under ambient atmosphere at600℃, and red-shifted first and then blue-shifted when samples were annealed under atmosphere at700℃. However, when samples were annealed at other temperatures under atmosphere, theemission peaks were still blue-shifted. Furthermore, when samples were annealed under methaneambience at various tempratures and for different time periods, the emission peaks were alwaysred-shifted. Besides, the shift span reached up to the maximum value when samples wereannealed under methane ambience at600℃for4hours. The fitting peak patterns of samplesannealed under methane confirmed that the luminescence properties were decided by threemechanisms, and the emission peak which was located at505-530nm,545-560nm and440-505nm respectively was caused by C-related defect, B-O luminescence center and other defects orvacancies, respectively.
Keywords/Search Tags:BCNO, luminescence materials, annealing, blueshift, redshift
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