Alumina-based Luminescent Materials

At the beginning ,according to the basic knowledge about phylogeny , definition , makeup , sorts , luminescent mechanism , preparing methods and applications of luminescence materials ,current research information and subsistent problems of luminescence materials at home and abroad were analyzed in this paper . Red fluorescence powders that use alumina as the matrix were regarded as our research emphases in order to reduce the price of red powders commercially and improve its performances .Research contents and results are as follows:Fluorescence powders were prepared by using Al(NO₃)-3·9H₂O as the main raw material and using NH₄HCO₃ and urea as the mixed precipitator to adoptthe reverse titration co-precipitation technology . Its performances were studied. The paper consists of four main parts .Firstly , the precursor NH₄AlO(OH)HCO₃ was prepared by this method that has been optimized. The study about preparing the precursor NH₄AlO(OH)HCO₃(indicates : when the concentration and the pH value of Al(NO₃)₃ solution are 0.2mol/L and 3～4 respectively ;when the concentration and the pH value of the mixed precipitator are 2mol/L and 9～10 respectively ;when the molar ratio of NH₄HCO₃ and Al(NO₃)₃ is 10 , the well dispersive , single phase and excellent performance precursor NH₄AlO(OH)HCO₃ can be obtained by the reverse slow titration (less than 0. 8L/h).Secondly ,the phase change of powders that were obtained by calcining the precursor NH₄AlO(OH)HCO₃ at different temperatures was studied through TG-DSC and XRD . The process of phase change is that : NH₄AlO(OH)HCO₃â†'amorphous aluminaâ†'γ-aluminaâ†'θ-aluminaâ†'α-alumina . Through excitation spectra and emission spectra of powders , we get that : When detected at wavelength 395nm ,excitation spectra of alumina matrix is a broad band from 220nm to 270nm at the center of 247nm . Under 254nm excitation, emission spectra of alumina matrix is also a broad band from 340nm to 460nm at the center of 395nm .When the calcining temperatures change ,the location of the peak does not change ,but the intensity changes strongly . The reason is that the luminescence intensity of F⁺ color center is effected by the two different mechanisms .When the excitation wavelength becomes bigger , the main peak of emission spectra has some red shift.Thirdly , the luminescence powders of Al₂O₃: Eu and Al₂O₃:Eu,Tb were prepared . Through TG-DSC, XRD, SEM and fluorescence spectrophotometer, their phases and luminescence property were studied .The results are that :When adding the rare earths of Eu or Tb , the phase change is greatly restrained and the thermal stability ofγ-Al₂O₃ becomes stronger . Adding quantity is more , the effects to the phase change and the crystallization process of alumina are bigger .When the Al₂O₃:Eu powder is calcined at 1050℃for 4h and concentration of Eu³⁺ dopant is 1mol% , Red fluorescence powder Al₂O₃:Eu that has the strongest luminescence intensity is obtained .Through experiments and analysis , the main peak at 614nm is the ⁵D₀- ⁷F₂ transition of Eu³⁺ ions . Adding Tb can improve the luminescence intensity of Al₂O₃: Eu powder. The optimum concentration of Tb³⁺ dopant is 5mol% .Fourthly , the luminescence powders of GdAlO₃:Eu and (Gd,Y)AlO₃:Eu were prepared and studied . Through TG-DSC, XRD and fluorescence spectrophotometer, their phases and luminescence property were studied . The results are that : The GdAlO₃:Eu powder calcined at 1200℃for 2h has high luminescence intensity and pure phase . When optimum concentration of Eu³⁺ dopant is 3mol%, the main emission peak is at 609nm (⁵D₀â†'⁷F₂) under 254nm excitation .With the calcining temperature increasing ,the luminescence intensity GdAlO₃:Eu becomes stronger. When a part of Gd³⁺ ions is substituted for Y³⁺ ions ,with phase inclining to single GdAlO₃ or YAlO₃, the luminescence intensity becomes stronger according to their emission spectra. They are good substitutes for red powder Y₂O₃:Eu .At last ,a simple expectation about farther work and direction of this subject was made .