Tb3+ and Eu3+ co-doped Ba6Bi9B79O138: color-tunable phosphors by utilizing the host-sensitization effect of Bi3+ and enhancement of red emission upon heating

Abstract

A series of Tb³⁺ and Eu³⁺ co-doped Ba₆Bi₉B₇₉O₁₃₈ (BBBO) phosphors were prepared by high-temperature solid-state reactions in order to utilize the host-sensitization effect of Bi³⁺. Energy transfer processes from Bi³⁺ in the host to both Tb³⁺ and Eu³⁺, as well as from Tb³⁺ to Eu³⁺ were proved. Under UV-excitation, three emissions can be simultaneously observed in a single-phase phosphor, including a blue band attributed to Bi³⁺ emission in the host, green lines due to Tb³⁺ transitions of ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3), and red lines due to Eu³⁺ transitions of ⁵D₀ → ⁷F_J (J = 1, 2, 3, 4). Thus, the total emission could be rationally tuned by varying the relative doping contents of Tb³⁺/Eu³⁺ and by selecting appropriate exciting irradiation. Thermal stability was investigated by in situ PL spectra at elevated temperatures. It is quite interesting to observe a significant enhancement of red emission in both BBBO:0.05Eu³⁺ and BBBO:0.05Tb³⁺,0.005Eu³⁺ excited at 279 nm. Especially in the latter case, the red emission intensity at 150 °C is roughly 3 times that at room temperature, which is explained by the increasing efficiency of Bi³⁺ → Eu³⁺ and Tb³⁺ → Eu³⁺ energy transfer upon annealing.