Synthesis and photoluminescence properties of (Y,Gd)Al3(BO3)4:Tb3+ under VUV excitation

Single phase of YxGd0.5−xTb0.5Al3(BO3)4 (0 ≤ x ≤ 0.5) was prepared by the thermal decomposition of the corresponding nitrates. The main broad band in 120–178 nm and some other bands in 178–288 nm were observed in the excitation spectrum of Gd0.5Tb0.5Al3(BO3)4 monitored at 541 nm. The former could be assigned to overlapped absorptions among the f → d transition of Gd3+, charge transfer bands of O2− → Ln3+ (Ln = Tb, Gd) and BO3 groups. The latter was ascribed to 4f8 → 4f75d transitions of Tb3+. Under 147 nm excitation the maximum emission peak was observed at about 541 nm in the emission spectrum of Gd0.5Tb0.5Al3(BO3)4, which was due to the 5D4 → 7F5 transition of Tb3+; when substituting Gd3+ with appropriate Y3+, the emission intensity of the 5D4 → 7F5 transition of Tb3+ increased, and the optimum emission was obtained at x = 0.1 in YxGd0.5−xTb0.5Al3(BO3)4. This could be due to that electronic transitions occurred from O2−:2p6 to Y3+:4p6 (4d + 5s) and the absorbed energy transferred to Tb3+ finally, as observed in the excitation spectrum of Y0.1Gd0.4Tb0.5Al3(BO3)4. The decay time of the 5D4 → 7F5 transition of Tb3+ decreased after Y3+ replacing Gd3+, which could be attributed to increasing defect impurities in Y0.1Gd0.4Tb0.5Al3(BO3)4 under 147 nm excitation.