Preparation And Properties Of Rare-earth Ions Doped Yttrium Aluminium Garnet And Yttrium Aluminium Borate

Both yttrium aluminium garnet (Y₃Al₅O₁₂, YAG) and Yttrium aluminium borate (YAl₃(BO₃)₄, YAB) have wide applications in the matrix materials of luminescent powder and laser due to their good properties of mechanics, thermotics and optics. In this paper, the YAG and YAB materials doped by rare earth ions were investigated systemically, respectively, and the relations between the powders synhesis processing, microstructure and properties were discussed. Results are obtained as follows:1. Nd: YAB powders were successfully synthesized by solid state reaction. The relations between main factors e.g., composition, calcined temperature and Nd³⁺ doping concentration and the properties of as-prepared powders were systemically studied. Results show that the monophase hexagonal powders of Nd: YAB powders were synthesized at 1200℃for 3h, with the mean particle size of about 2μm, using the Al₂O₃, Y₂O₃, Nd₂O₃ and H₃BO₃ with more 40at% as the starting materials. The lattice constant of Nd:YAB increases as the doping concentration of Nd³⁺ increases. The crystalline structure of prepared powders transfers the monocline when the concentration of Nd³⁺ is greater than 80%.2. The Nd:YAB powders were synthesized by nitrate pyrogenic decomposing using Al₂O₃, Y₂O₃, Nd₂O₃ and H₃BO₃ (more than 20at%) as the starting materials. The results of XRD show that Nd:YAB powders with single phase were synthesized at 1100℃for 2h. It is found that the intermediate phases of Al₄B₂O₉, YBO₃ and Y₃Al₅O₁₂ are generated firstly, and then YAB phase is produced in the synthesis process.3. By sol-gel combustion, Nd: YAB powders were synthesized at lower temperature of 1000℃using citric acid as the complexing agent, and the gel technique and reaction mechanism were studied. Results show that the molar ratio of nitrate to citric acid has a greater influence on the phase changes in the synthesis process and particle sizes and morphologies of the prepared powders. The Nd:YAB powders synthesized at 1100℃have the particles with the size of about 800nm and good dispersivity when the molar ratio of nitrate to citric acid is 1: 1.5. The citric acid will result in the heavy agglomerate of powder particles when its amount is less or greater than this optimum ratio.4. Single phase YAB:RE³⁺ (RE=Eu, Tb) phosphors were synthesized by sol-gel combustion, with homogeneous particle sizes and good dispersivity. The luminescence properties excited under ultraviolet(UV) and vacuum ultraviolet(VUV) were investigated. Results show that there exists more absorption for the phosphors of YAB: RE³⁺ under UV and VUV excitation. YAB: Eu³⁺ and YAB: Tb³⁺ emit red and green lights under UV excitation, corresponding to the transition emissions of ⁵D₀→⁷F₂ of Eu³⁺ and ⁵D₄→⁷F₅ of Tb³⁺, respectively. Furthermore, the photoluminescence intensities increase firstly, and then decrease with increasing doping amounts of Eu³⁺ (Tb³⁺) ions and calcined temperatures. Through comparing the luminescence properties of the YAB:Eu³⁺ phosphors by solid state reaction, pyrogenic decomposition of nitrate and sol-gel combustion methods, respectively, it is found that the phosphor by sol-gel combustion has the fine particle morphology and luminescence efficiency. Additionally, due to the energy transformations of Gd³⁺→Eu³⁺ and Gd³⁺→Tb³⁺ in YAB:Eu³⁺ and YAB:Tb³⁺, respectively, the photoluminescence intensities of YAB:RE³⁺ (RE=Eu,Tb) are improved greatly after doping Gd³⁺ ion.5. The Nd:YAG powder with single phase was synthesized at lower temperature of 900℃by sol-gel and combustion method, and the intermediate phases were not generated in the synthesis process. The Nd:YAG powder has the sphere like nano-size particle when the calcined temperature is up to 1000℃, with the mean size of about 60nm and good dispersibility.The effect of sintering technique on the densification and microstructure of Nd:YAG ceramics prepared by the above powders was studied. Results show that the relative density of Nd:YAG increases with increasing temperature. The relative density of 99.5% is obtained when the temperature is 1700℃. Furthermore, the additive of tetraethyl orthosilicate (TEOS) has a significant influence on the densification of the ceramic in the sintering process. Results show that the optimum density is achieved when the doping concentration of TEOS is 0.3wt%, and that the second phase in grain boundary is not found and the additive serves as the suppression of grain growth. The Nd:YAG ceramic prepared at 1700℃for 20h has an optical transmission as high as 62% at 1064nm.6.The phosphors of YAG:RE³⁺ (RE=Eu,Tb) were synthesized by sol-gel combustion, and their optical spectra under VUV were investigated. Results show that The phosphors of YAG:RE³⁺ (RE=Eu,Tb) have more absorption under VUV, which are mainly caused by the absorption of matrix. Under the excitation of 147nm, the phosphors of YAG:RE³⁺(RE=Eu,Tb) emit stronger orange light and green light, corresponding to transition emissions of ⁵D₀→⁷F₁ of Eu³⁺ ion and ⁵D₄→⁷F₅ of Tb³⁺ ion, respectively, and their photoluminescence intensities increase firstly, and then decrease with increasing concentration of rare earth ions(Eu³⁺, Tb³⁺). The optimum amount of doping for Eu³⁺ and Tb³⁺ are 4at% and 3at%, respectively. Meanwhile, the effect of the temperature of heating treatment on photoluminescence property was studied at doping concentration of the same rare earth ion. Results show that the photoluminescence intensities of the phosphors increase as the temperature of heating treatment increases.