(Ba,Sr)TiO3:RE perovskite phosphors (RE = Dy, Eu): nitrate pyrolysis synthesis, enhanced photoluminescence, and reversible emission against heating

Abstract

A series of (Ba,Sr)TiO₃ phosphors singly doped with Eu³⁺ and Dy³⁺ were successfully synthesized using the nitrate pyrolysis method at 750 °C. Eu³⁺ or Dy³⁺ single-doped BaTiO₃ retained the tetragonal crystal structure of the host, while the Sr²⁺-substituted (Ba,Sr)TiO₃:RE³⁺ (RE³⁺ = Eu³⁺ or Dy³⁺) experienced a phase transformation from tetragonal to cubic phase with a unit cell shrinkage. For Eu³⁺ doped phosphors, BaTiO₃:xEu³⁺ (x = 0.02–0.10) exhibited red photoluminescence and the highest intensity of emission belonged to the optimal-doped BaTiO₃:xEu³⁺ (x = 8 mol%). Moreover, the substitution of 30 mol% Sr²⁺ for Ba²⁺ (that is Ba_0.7Sr_0.3TiO₃:xEu³⁺, x = 8 mol%) further enhanced the emission intensity of BaTiO₃:xEu³⁺ (x = 8 mol%). For Dy³⁺ doped phosphors, BaTiO₃:xDy³⁺ (x = 0.02–0.10) showed yellow photoluminescence and the highest light intensity was from the optimal-doped BaTiO₃:xDy³⁺ (x = 4 mol%). In addition, the substitution of 20 mol% Sr²⁺ for Ba²⁺ (the phosphor Ba_0.8Sr_0.2TiO₃:xDy³⁺, x = 4 mol%) induced further increase in emission intensity of BaTiO₃:xDy³⁺ (x = 4 mol%). The emission intensities at higher temperature of 100 °C retained about 70% and 90% of the initial values at room temperature (RT) for the optimal BaTiO₃:xEu³⁺ (x = 8 mol%) and BaTiO₃:xDy³⁺ (x = 4 mol%) phosphors, respectively, while the emission intensities at the temperature of 100 °C retained about 60% and 80% of the initial intensities at RT for the optimal Sr²⁺-substituted Ba_0.7Sr_0.3TiO₃:xEu³⁺ (x = 8 mol%) and Ba_0.8Sr_0.2TiO₃:xDy³⁺ (x = 4 mol%) phosphors, respectively. It is worth noting that on cooling down to RT again from 210 °C, the BaTiO₃:xDy³⁺ (x = 4 mol%) phosphor exhibited excellent luminescent thermal stability (with a high activation energy of 0.387 eV) and the strongest recovery (∼95%) of PL emission among the series of phosphors. The as-prepared phosphors with optimal compositions would be good candidates for the applications in lighting, display, and related fields.