Enhancing the upconversion of Er 3+ incorporated BaTiO 3 by introducing oxygen vacancies.

Lanthanide-incorporated crystals display the phenomenon of upconversion (UC), wherein near-infrared (NIR) light is converted into ultraviolet-visible (UV-Vis) emission with a narrow bandwidth. This unique photophysical property renders lanthanide UC materials highly promising for diverse applications. However, the limited quantum efficiency (∼3%) hinders the broader utilization of UC materials. Consequently, numerous studies have focused on overcoming this low efficiency. Notably, it has been observed that manipulation of the site symmetry in UC materials significantly enhances their UC efficiency. In this study, we investigate the UC enhancement of Er 3+ incorporated BaTiO 3 (E-BT) crystals through the introduction of oxygen vacancies (O V ). The O V were created using a post-heat treatment method, and the annealing time was varied to control the quantity of O V . An optimal annealing time of 6 hours was determined for efficient O V generation, beyond which the O V content decreased. Remarkably, E-BT crystals with O V exhibited up to three-fold greater UC compared to those without O V . This outcome suggests that O V induce symmetry changes in the E-BT crystal structure. Furthermore, the degree of UC enhancement in E-BT was found to be proportional to the amount of O V present.