关键词: bismuth layered structure, positron annihilation lifetime spectroscopy, upconversion photoluminescence, vacancy clusters

Abstract: Doping of rare earth elements into Bi$_{4}$Ti$_{3}$O$_{12}$ can significantly enhance the upconversion photoluminescence (UCPL) properties, but its structure-property relationship is still unclear. In this work, Er-doped bismuth titanate Bi$_{4-x}$Er$_{x}$Ti$_{3}$O$_{12}$ ($x=0$, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics were synthesized via solid-state reaction method. The x-ray diffraction analysis confirmed the orthorhombic crystalline structure of the Bi$_{4-x}$Er$_{x}$Ti$_{3}$O$_{12}$ ceramics without any secondary phases. Experiments and calculations of positron annihilation spectroscopy were carried out to characterize their defect structure. The comparison between the experimental and calculated lifetime revealed that vacancy clusters were the main defects in the ceramics. The increase of the intensity of the second positron lifetime component ($I_{2}$) of Bi$_{3.5}$Er$_{0.5}$Ti$_{3}$O$_{12}$ ceramics indicated the presence of a high concentration of vacancy clusters. The UCPL spectra showed the sudden enhanced UCPL performance in Bi$_{3.7}$Er$_{0.3}$Ti$_{3}$O$_{12}$ and Bi$_{3.5}$Er$_{0.5}$Ti$_{3}$O$_{12}$ ceramics, which were consistent with the variation of the second positron lifetime component ($I_{2}$). These results indicate that the enhanced UCPL properties are influenced not only by the concentrations of rare earth ions but also by the concentration of vacancy clusters present within the ceramics.

Key words: bismuth layered structure, positron annihilation lifetime spectroscopy, upconversion photoluminescence, vacancy clusters