Efficient green luminescence in Tb3+-activated borates, A6MM′(BO3)6

Photoluminescence of several new green-emitting Tb3+-activated borates of the type Sr6MM′(BO3)6 [A = Sr; M = Gd, Y; M′ = Al, Ga, In, Sc, Y] and LaSr5MM′(BO3)6 [A = Sr, La; M = Y; M′ = Mg] with Tb3+ at the M or M′ site has been studied and the results are presented here. All these borates are synthesized by the solid state reactions under reducing atmospheres and are characterized by powder XRD, density, TG/DT, particle size analysis and photoluminescence techniques. These borates are synthesizable at temperatures below 1000 °C as evidenced by thermal studies and are found to have narrow range of particle sizes (5–15 μm). The photoluminescence excitation spectra of these borates show a broad band at ∼257 nm due to 4f–5d transition of Tb3+ ion, which also depends on Tb3+ concentration. Under excitation with 254 nm, all these borates display high intense green emission at 542 nm due to 5D4–7F5 transition of Tb3+ ion. The influence of ions doped at the M′-site on the luminescence of Tb3+ is also studied. The luminescence properties of all these borates have been compared with each other and with the standard phosphor, LaCePO4:Tb3+. The results show that these borate phosphors have several advantages over the standard green phosphors. Thus, the group of Tb3+-activated hexaborate phosphors is an efficient alternative to the existing commercial green phosphors for use in tri-color low pressure mercury vapor lamps.