退火对Tb掺杂ZnAl层状双金属氢氧化物的结构和荧光特性的影响

Effects of annealing on structure and fluorescence of Tb-doped ZnAl LDHs

采用共沉淀法制备Tb^(3+)掺杂的锌铝水滑石(Tb-ZnAl-LDH),然后将Tb-ZnAl-LDH分别在200、400、600、800、1 000℃进行退火处理。X射线衍射(XRD)测试结果发现:200℃时Tb-ZnAl-LDH的层状结构发生坍塌,400℃时层板断裂,并出现ZnO相。随着退火温度的升高,ZnO相的衍射峰增强,到1 000℃时出现尖晶石(ZnAl_2O_4)结构。荧光光谱(FL)结果表明:原生Tb-ZnAl-LDH呈现很强的绿光,该绿光源于Tb^(3+)离子的5D4-7FJ(J=3,4,5,6)跃迁。经200℃退火后,源于Tb^(3+)的绿光峰大大减弱;当退火温度增加至400℃时,这些分立的绿光峰消失,出现很宽的峰(450~650 nm)。这些研究结果表明,层状ZnAl LDH主体材料更有利于Tb^(3+)离子的发光。此外,扫描电镜(SEM)观察发现,当Tb-ZnAl-LDH的退火温度达到400℃时,其形貌开始出现明显的改变。

Tb^（3＋）doped zinc aluminum layered double hydroxide（ Tb-ZnAl LDH） was prepared by the co-precipitation method,and the Tb-ZnAl-LDH was annealed at 200,400,600,800,and 1 000 ℃,respectively. X-ray diffraction（ XRD） results revealed that the layered structure of Tb-ZnAl-LDH collapsed at 200 ℃; the layers of LDH broken at 400 ℃,and ZnO phase occurred. With the annealing temperature increased,the diffraction peaks attributed to ZnO phase became stronger,and the spinel structure ascribed to ZnAl_2O_4 appeared as the annealing temperature increased to 1 000 ℃. Fluorescence spectra showed that the as-prepared Tb-ZnAl-LDH exhibited strong green emissions due to ~5D_4-~7F_J（ J = 3,4,5,6） transition of Tb^（3＋）. After annealing at 200 ℃,the green emissions greatly decreased. As the annealing temperature increased to 400 ℃,the green emission due to Tb^（3＋）ions disappeared,and a broad peak at 450- 650 nm appeared. These results indicated that the layered ZnAl LDH was more favorable for the fluorescence of Tb^（3＋）. In addition,scanning electron microscopy（ SEM） suggested that the morphology of TbZnAl-LDH changed obviously as the annealing temperature increased to 400 ℃.