Boosting Upconversion Photoluminescence and Multielectrical Properties via Er-Doping-Modulated Vacancy Control in Ba_0.85Ca_0.15Ti_0.9Zr_0.1O₃

The lead-free 0.5(Ba_0.7Ca_0.3)TiO₃-0.5Ba(Ti_0.8Zr_0.2)O₃ (BCTZ) ceramics with Er doping have shown good upconversion photoluminescence (PL) and desirable optical temperature sensing properties. To bridge a relationship between the structure/intrinsic defects and properties of rare-earth-doped ferroelectrics, we designed and fabricated a series of BCTZ ceramics doped with 1 mol % Er³⁺ by combining the first-principles calculations and experimental measurements. Theoretically, we discovered that Er can occupy both A sites (i.e., replacing Ba or Ca) and B sites (i.e., replacing Ti or Zr) in the BCTZ lattice and highlighted that the Er-doping-induced vacancy concentration decreases for both the oxygen vacancies (V_o) and cation vacancies (V_c). Experimentally, the enhanced PL performance and the dielectric, ferroelectric, and piezoelectric properties of the Er-doped BCTZ ceramics have been observed. Finally, the physical origin of Er-induced property enhancement in BCTZ has been elaborated according to the charge density and chemical bonding analysis. These results open up a path to investigate the effects of site substitution and vacancies on optoelectronic properties of multifunctional rare-earth-doped ferroelectrics.