Study On Synthesis And Puminescent Properties Of Aluminate

With the development of human sociaty,higher and higher lighting and display brightness are needed.In lighting and display technology,luminescent materials are the key to determine the product performance.Aluminates,silicates and emerging(oxygen)nitride systems are widely used luminescent materials at the present time.Although the development of new(oxygen)nitride luminescent materials is expanding the number of luminescent materials,the improvement of traditional aluminate and silicate luminescent material preparation techniques and optimization of their performance are still one of the effective ways to obtain high-performance luminescent materials.Due to the variety of traditional aluminates,the correlation among them are not been studied deeply.Therefore,the efforts are made on the study of the preparation process of various aliminates and their fluorescence properties in order to optimize the products performance and simplify the materials process in the dessertation.Firstly,the sol-gel method was used to prepare CaAl4O7:Eu3+,Tb3+,Ce3+ phosphors,and the effects of changes in synthesis temperature,rare-earth ion doping concentration,and types of solvents on the crystal structure and luminescent properties of phosphors were investigated.The XRD results show that the pure phase of CaAl4O7 can be synthesized at a temperature as low as 800?.Fluorescence spectra indicate that CaAl4O7:Eu3+has a strong emission peak at 614 nm due to 5Do?7F2 transition of the Eu3+ ion at the 232nm excitation,indicating that the Eu3+ occupies an asymmetric lattice site in CaAl4O7.The excitation of CaAl4O7:Tb3+at 220 nm is the strongest emission peak at 545 nm corresponds to the 5D4?7Fs transition of the Tb3+ion.And it emits yellow-green light.The excitation of CaAl4O7:Ce3+at 273 nm,the strongest emission peak at 369 nm corresponds to the 4f1?5d1 transition of the Ce3+.Secondly,Ca1-xSrxAl4O7:0.05Eu3+ red phosphor was prepared by a sol-gel method at a synthesis temperature of 1000?.The effects of Sr2+ incorporation and solvent type on the crystal structure,morphology and luminescent properties of CaxSr1xAl4O7:0.05Eu3+ phosphors were investigated.XRD results show that 30%Sr can enter the crystal lattice at 1000? heat treatment temperature,and the crystal lattice can remain stable.When the doping level of Sr exceeds 30%and ethylene glycol as the solvent,the SrAl2O4 phase appears.Under this doping level and water as the solvent,Sr3Al2O6,SrAl2O4,Al2O3 phase will appear.The optimum phosphor Sr content obtained was 30%.Since the introduction of Sr2+ causes the lattice expansion,and the introduction of Eu3+causes the lattice to shrinkage,the introduction of Sr can increase the probability of Eu ions entering the lattice.In this case,when the Sr content is 30%,the lattice maintains the original phase.Instead of producing a heterophase,the effective concentration of the Eu3+-into-lattice is maximized,thus causing the maximum photoluminescent intensity,at the same time,crystal cell expends slightly.Its luminescent intensity is about 2-3 times that of CaAl4O7:0.05Eu3+.The peak position of the excitation spectrum shifts to the right with the increase of Sr2+concentration.When the ethylene glycol is solvent,the peak position of the emission spectrum is not shifted.When the water is solvent,the peak position of the emission spectrum is red-shifted and widened.At the same time,the addition of Sr2+ ions has a significant effect on the morphology of the samples in different solvents.The higher the concentration of Sr2+,the phenomenon of agglomeration of phosphors is more obviously.The morphology of the sample prepared by ethylene glycol solvent is agglomerated coral shape and deionized.The shape of the sample prepared by using water as a solvent is a non-uniform block structure and gradually grows.It is difficult to synthesize BaA1407 in this system,and a mixture containing BaAl2O4 and Al2O3 is usually formed.Therefore,Bal2O4 is the most stable and most convenient to be obtained in the BaO-Al2O3 system.Finally,BaAl2O4:Eu3+/Eu2+ phosphors were successfully prepared by solid-phase method.The effects of oxidation/reduction atmosphere,synthesis temperature and rare earth ion doping concentration on the crystal structure,morphology and luminescent properties of the phosphors were investigated.The experimental results show that the BaAl2O4 phase can be synthesized at 650?,and the pure BaAl2O4 powder can be obtained when the synthesis temperature reaches 1000?.The morphology of the phosphor is an irregular block structure varying in diameter from 1 micron to several micrometers,and the particle size gradually grows as the heat treatment temperature increases.Fluorescence spectroscopy indicated that the emission peaks of the prepared BaAl2O4:Eu3+phosphors were located at 595,613 and 618nm,respectively.The strongest peak at 595nm corresponds to the 5D0?7F1 transition of Eu3+,showing orange light emission.Strong emission peaks at 613nm and 618nm also indicate that Eu3+ions occupy a lower symmetry Ba2+ sites.Its optimum synthesis temperature is 1000?.The emission peak of BaAl2O4:Eu2+ phosphor is located at 497nm corresponding to the 4f65d?4f7 transition of Eu2+,showing green luminescence.The optimum synthesis temperature is 1200?,the optimum temperature for secondary heat treatment is 1000?,and the optimum doping concentration of Eu2+is 2%.Co-doping with Dy3+can significantly improve the luminescence intensity and fluorescence lifetime.