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Investigation Of Rare Earth Doped Ca2SnO4 And CaSnO3 Long-persistent Luminescent Materials: Synthesis, Properties And Luminescence Mechanisms

Posted on:2017-02-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:X P GaoFull Text:PDF
GTID:1221330503462796Subject:Materials Science and Engineering
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In this thesis, the novel rare earth-doped Ca2SnO4 and CaSnO3 long-persistent luminescent materials with blue, green-white, red, and white afterglow were synthesized by high temperature solid state reaction in air atmosphere and in vacuum argon gas atmosphere, respectively. The effect of oxygen vacancy on luminescent properties and the mechanism was also investigated.The new long-persistent luminescent materials of Ca2-xSnO4: xLn3+(Ln3+=Y3+, La3+, Gd3+, Lu3+) with blue afterglow and Ca1-xSnO3: xLn3+(Ln3+=Y3+, La3+, Gd3+, Lu3+) with greenish-white afterglow were synthesized by high temperature solid state method in air atmosphere and vacuum argon gas atmosphere, respectively. These two types of phosphors exhibit brand emission band of 350550nm and 400650nm, respectively. Among the above mentioned phosphors, Ca2SnO4: Gd3+ sintered in vacuum argon gas atmosphere has the longest afterglow time of 3 hours(the time required for luminance intensity larger than 0.32 mcd/m2). Its maximum emission wavelength is around 400 nm, and its chromaticity coordinate is(x=0.171, y=0.144) blue. It can be utilized as excitation source for inorganic or organic luminescence system, and for photo-catalytic materials in dark place. It is found that oxygen vacancy can improve the luminescent properties of Ca2SnO4: Ln3+ with one dimensional chain structure, but oxygen vacancy can quench the afterglow luminescence of CaSnO3: Ln3+ with three dimensional network structure.The new long-persistent luminescent materials of Ca2SnO4: Eu3+ and Ca2SnO4: Eu3+, Gd3+ with red afterglow were synthesized by high temperature solid state method in air atmosphere and vacuum argon gas atmosphere, respectively. Vacuum sintering prolonged the persistence time of Ca2SnO4: Eu3+, Gd3+ and Ca2SnO4: Eu3+ to 108 minutes and 51 minutes, respectively. The chromaticity coordinate of the former is(x=0.428, y=0.307) pink, and that of the latter is(x=0.53, y=0.348) yellowish-pink. A new form of persistent energy transfer in Ca2SnO4: Eu3+, Gd3+ was found, that is from the self-trapping exciton states’ emission induced by Gd3+ to Eu3+. It is also found that the introduction of Gd3+ changes the ration of the red emission intensity to orange emission intensity Eu3+(5D0â†'7F2)/(5D0â†'7F1), which means that the single doping rare earth ion in Ca2SnO4 prefers occupying the low symmetry site of Ca2+ and partly occupying the high symmetry site of Sn4+, while Gd3+ and Eu3+ are co-doped, Gd3+ prefers occupying the site of Ca2+, and then some of Eu3+ will be pushed into the site of Sn4+.The new long-persistent luminescent materials of Ca2SnO4: Dy3+ and CaSnO3: Dy3+ with white afterglow were synthesized by high temperature solid state reaction in air atmosphere and vacuum argon gas atmosphere, respectively. The Ca2SnO4: Dy3+ samples sintered in air atmosphere have different colors like purple and white in according with different doping concentrations. These phosphors have the longest persistence time of 14 minutes. The CaSnO3: Dy3+ samples sintered in air atmosphere have the highest initial light level of 0.16 cd/m2 and longest persistence time of 30 minutes. Vacuum sintering enhances the afterglow performance of Ca2SnO4: Dy3+ and prolongs the persistence time to 170 minutes, with the chromaticity coordinate(x=0.4007, y=0.4293) yellow-white. However, vacuum sintering quenches the afterglow luminescence of CaSnO3: Dy3+.The Matrix of Ca2SnO4, Sr2CeO4 and CaSnO3 were synthesized by high temperature solid state method in air atmosphere and vacuum argon gas atmosphere, respectively. It is first found that Ca2SnO4 sintered in air atmosphere has strong blue fluorescence, with chromaticity coordinate(x=0.4007, y=0.4293) yellow-white, under 336 nm light excitation, This type of luminescence is induce by emission of the charge-transfer state(CTS) from terminal O to Sn, which is due to the one dimensional chain structure formed by SnO6 octahedron. In contrastCaSnO3 with three dimensional network structure formed by SnO6 octahedron, has no luminescence. It is also found that both of Ca2SnO4 and CaSnO3 sintered in vacuum have no luminescence, while both of Ca2SnO4 and Sr2CeO4 with tri-rare-earth ions sintered in vacuum have greatly improved luminescence properties due to the one dimensional chain structure formed by CeO6 octahedron. The effects of oxygen vacancy, trivalent rare earth ions and crystal structure on luminescent properties were speculated, and the luminescence mechanisms were investigated by the X-ray photoelectron spectroscopy(XPS) energy spectrum analysis.
Keywords/Search Tags:polychrome persistent luminescence, vacuum sintered, oxygen vacancy, Ca2SnO4, CaSnO3, crystal defect clusters, X-ray photoelectron spectroscopy(XPS), thermo-luminescence spectrum
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