Effects of vacancies on luminescence of Er-doped 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ceramics

0.93Bi0.5Na0.5TiO3-0.07BaTiO3ceramics doped with 0.01 mol Er3+have been prepared and their photoluminescence (PL), ferroelectric, dielectric, and piezoelectric properties have been studied. By doping Er3+at various sites, ceramics containing oxygen or cation vacancies have been prepared and their effects have been investigated. Ceramic containing no vacancy (i.e., doping Er3+at the Bi3+site) has also been prepared as a reference for the study. In addition to the reduction of the up-conversion PL emissions at 532, 547, and 660 nm, our results also reveal that oxygen vacancies can enhance, at the expense of the visible emissions, the near-infrared (1.44-1.66 μm) and mid-infrared (2.62-2.84 μm) down-conversion emissions. Similar results have also been observed for the ceramics containing cation vacancies, and the enhancement in the near-infrared emission becomes much more significant, reaching about 70% for the ceramic doped with Er3+at the Na+site. These should be attributed to the looping mechanism between the4F7/2,2H11/2,4I9/2, and4I11/2levels facilitated by the cation vacancies and the efficient cross relaxations. The ceramics also exhibit reasonably good ferroelectric, dielectric, and piezoelectric properties, suggesting that they have great potential for multifunctional applications.