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

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 D-5(4) -> F-7(J) (J = 6, 5, 4, 3), and red lines due to Eu3+ transitions of D-5(4) -> F-7(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:0.05Eu(3+) and BBBO:0.05Tb(3+), 0.005Eu(3+) excited at 279 nm. Especially in the latter case, the red emission intensity at 150 degrees 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.