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Luminescent Properties Of Eu、Dy Doped MAl12O19(M=Ba, Sr,Ca) Long Afterglow Phosphors

Posted on:2013-08-30Degree:MasterType:Thesis
Country:ChinaCandidate:Y XiongFull Text:PDF
GTID:2181330371981240Subject:Materials Physics and Chemistry
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Long afterglow material is one kind of energy storage materials which has the capability of storing energy. It has a long time afterglow luminescence after the closure of the excitation source. Long afterglow material is widely used in many fields such as the instrument display panel, theater, subway, airport, large shopping malls and other public places emergency indicating and lighting, safety signs, traffic marking, decoration and other aspects, and it is also gradually expanded to the information storage, high energy ray detection in recent years. The two kinds of main long afterglow luminescent materials which are commercial applied now are aluminates and silicates. With its long afterglow time, nontoxic, high chemical stability and other advantages, aluminate long afterglow materials have attracted much attention, and have already made great economic benefits, but for now, aluminate long afterglow materials still exist problems such as luminous color is single, the afterglow mechanism is unknown, and some other shortcomings, therefor we still need to do much further research and development for the material.The alkaline earth aluminate long afterglow materials that have been developed or are being developed in recent years are mainly activated by Eu2+.In general, Eu2+was used as luminescent center. The electron configuration of Eu2+ion is4f75s25p65d0and the luminescence of Eu2+is electron transition by4f65d'4f7. The energy level of5d is very sensitive to the change of crystal field due to the naked electronic shell. So, the split of5d energy level is quite different in different matrix crystalline field, and the luminescence wavelength of Eu2+is quite different. In this work, rare-earth-doped BaAl12O19is synthesized by a high temperature solid state method for our researches. Firstly, we have study the luminescence of BaAl12O19:Eu2+/Eu3+, Dy3+prepared under different atmosphere and the self-reduction reaction in the materials. Secondly, according to the emission wavelength of Eu2+is quite different in different matrix crystalline field, we study the Structure, photoluminescence and afterglow luminescence of the samples with different Ba/Sr and Ba/Ca ratio by the way of matrix replacement. And the mechanism of long persistence also has been discussed, according to the result of thermoluminescence spectra.Long afterglow phosphors BaAl12O19:Eu2+/Eu3+, Dy3+were synthesized by high temperature solid state method under different atmosphere. X-ray powder diffraction (XRD) shows that pure BaAl12O19phase structure was obtained and the doping ions Eu2+/Eu3+, Dy3+didn’t change the phase structure. We found the doping ions Eu2+/Eu3+, Dy3+caused XRD diffraction peaks moving to the high angle slightly which displayed that the inter-planar crystal spacing was changed by Eu、Dy replacing Ba lattice in BaAl12O19. Emission spectrums show that all the samples prepared under different conditions exist4f65d'4f7broadband transition which is the features emission of Eu2+.It indicates that Eu3+ions can be reduced to divalent state in air. The doping ions Dy3+can not only enhance the luminous intensity of samples but also make the samples obtaining long afterglow characteristics. The afterglow decay and thermoluminescence studies of the Eu, Dy co-doped sample synthesized under reducing atmosphere reveal that the sample has good long afterglow properties at room temperature and high temperature.Phosphors MAl12O19:Eu2+, Dy3+(M=Ba,Sr,Ca) were synthesized by high temperature solid state method under weakly reducing atmosphere. X-ray powder diffraction (XRD) shows that pure hexagonal structure MAl12O19(M=Ba,Sr,Ca) phases were obtained, they belong to P63/mmc (194) space group and have the same phase structure. Emission spectrums show that Eu2+is the only luminescence center in the samples, and emission spectrum of MAl12O19:Eu2+, Dy3+(M=Ba, Sr, Ca) were broadband peaking at440nm(M=Ba)、415nm(M=Ca)、395nm(M=Sr). The samples’ emission peaks can be continuously adjusted from395nm to440nm by changing the ratio of Ba, Sr and Ba, Ca in matrix. The afterglow decay curve and thermoluminescence studies reveal that the same phase structure samples have very different afterglow properties. Phosphors with long afterglow properties must have suitable trap levels and the trap density must be high enough, so that BaAl12O19:Eu2+, Dy3+with both suitable trap levels and high enough trap density has long afterglow, and CaAl12O19:Eu2+,Dy3+and SrAl12O19:Eu2+,Dy3+without high enough trap density have no long afterglow.BaAl12O19with Eu was synthesized by high temperature solid state method in the air. The ratio of Eu2+and Eu3+was studied by changing the doping concentration of Eu2O3. According to the charge compensation principle, low valence positive ions Na+or high valence ion of Si4+was doped in the sample to promote or inhibit the self-reduction reaction of Eu3+. Experimental results show as follow.(1) The maximum Eu3+occurred self-reduction reaction when the doping concentration of Eu was2%, and the ratio of Eu3+occurred self-reduction reaction was reduced as the Eu doping concentration gradually increased. When the doping concentration of Eu is6%or over6%, self-reduction reaction won’t happen in the samples.(2) Because of the un-equivalent substitution, internal electric field will keep neutral to reduce internal energy through controlling the ratio of Eu3+occurred self-reduction reaction, so that the doped Si4+can promote Eu3+occurred self-reduction reaction, and the doped Na+will inhibit the self-reduction reaction of Eu3+.
Keywords/Search Tags:Aluminates long persistent phosphors, Luminescent properties, High-temperature solid-phase synthesis method, Thermoluminescencespectra, traps
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