Luminescence and energy transfer properties of Gd3+ and Tb3+ in LaAlGe2O7

The novel phosphors of LaAlGe2O7 doped with Gd3+ and Tb3+ were synthesized, and their luminescence properties were investigated. In Tb3+-activated LaAlGe2O7, the unusual excitation spectra showed only intense f-f transition of Tb3+ ions around the near-UV region, whereas the 4f-5d transition could be neglected. In the Gd3+-Tb3+-activated system, the decay time of Tb3+ emission under Gd3+ excitation at the I-6(J) energy level was longer than that measured under direct Tb3+ excitation at the L-5(10) energy level, which reinforces the existence of effective Gd3+-to-Tb3+ energy transfer. In the D-5(4) decay measurements, time-resolved spectra exhibited a grow-in behavior as the Tb3+ concentration was diluted (< 0.03 mol), whereas only a simple exponential decay could be observed at higher (> 0.05 mol) Tb3+ concentrations. Two linear relationships were found between the energy transfer probability (P-Gd -> Tb) and the Tb3+ concentration, which is clear evidence that there were two kinds of efficient Gd3+-to-Tb3+ energy transfer processes in terms of Tb3+ concentration.