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Rare-earth Doped Strontium Aluminate Luminescence Materials Prepared From Pseudo-boehmite Sols

Posted on:2005-03-02Degree:MasterType:Thesis
Country:ChinaCandidate:J CaoFull Text:PDF
GTID:2121360125451436Subject:Non-ferrous metallurgy
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The processes and mechanism of preparing rare earth doped strontium aluminate luminescence materials from Pseudo-boehmite sols are investigated. In comparitions of solid phase synthesis and microwave synthesis, the pseudo-boehmite sols possesses the characteristics of lower cost and easy control . Because the relationships of process - structure - property is not very clear, it is significant scientifically and technologically to the understanding the processes.The Pseudo-boehmite powders are from the China Great-wall Aluminium Industry Co.Ltd., The preparation process is described as follow: The transparent and stable aluminum oxide sol is made by way of controlling solid content and acidity under the optimized process parameters. By adding rare earths to the sols,the gel turns into xerogel by dehydrate at 120 C, The weak reduction calcination is carried out in a horenzontal furnace. The experimental result shows that the synthesis temperature is lowed.The process parameters for sol-gel route were studied systemtically.Thedifferent calcining manner has little effect on the formation of Eu2t luminescence center, but adversely on Dy'+, Fedding dry gel at the target temperature can get to a suitable trap energy level. This manner not only strengthen the luminescence capability of materials , but also energy saving.We find the optimized calcining duration is for 1. 5h by deacy curve measurements. It' s brightness still achieves 0. 35409mcd/m" untill 24h. But the brightness of sample with Ih calcining time is smaller than 0.32 mcd/m2 after 13h.The formation of various phases during the processing is analyzed according to the phase diagram of SrO- A1A; the reduction mechanism of Eu~+ and the roles of BA are approached, The XRD patterns, DTG pattern and decay curve of as-synthesized sampleshave been measured.In particular, the role of B20:! on the phase formation is approached. It is generally believed that the flux is usually used to accelerate a solid state reaction in synthesizing long phosphorescent SrAlA: Eu2+, Dy'+ phosphor. We conclude that:(1) B203 has little effects on luminous behavior when BAi is in small amount(2) B203 will react with SrAl2O4 and Dy2O3 as follow:DyA+SrAlA+ B2O3= SrBA+ Dy4Al2O9The B203 should be controlled to small amount as the long afterglow luminous behavior is weakened with the increase of BA.(3) The optimum content of B203 in the end product is about 4% according to this experiment .It was found that SrAl2O4 : Eu2+, Dy3+ appeared luminescence quenching phenomenon when Sr,,Al207 phase formed. According to the experiment, we conclude that this phenomenon can be controlled when SrO/Al2O3(mol) is about 0.34.Baseded on the formation law of phases and experiment fact , we have a view point about the reducing process of Eu3+-Eu2+. Namely, it is not the effect of reducing gas directely, but the interaction of electron and Eu3+, then reduced. The electron comes into the atom track of Eu2+, the 4f of Eu2+ is athalf-abound, so it is very stable.In a word , the SrAl2O4: Eu2+, Dy3+phosphor with excellent physical - chemical properties has been synthesized successfully with Pseudo-boehmite sols .For the first time, the industry product (Pseudo-boehmite) has been used as primary materials, With this method , the calcining temperature can be lowred to 1200 癈. Because the primary material are all the inorganic salt, this method can avoid the pollution of the environment effectively.The laboratory-scale experimental results can provide valuable references for further scaling-up application.
Keywords/Search Tags:pesuo-boehmite, Rare earths, phase identification, long afterglow luminescence, phosphorescent mechanism
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