Tb3+→Eu3+ energy transfer processes in crystals of TbAl3(BO3)4 doped with Eu3+

In this contribution, the dynamics of the energy transfer process involving Tb 3+ ion in samples of trigonal huntite-type Tb 1-x Eu x Al 3 (BO 3 ) 4 (with x = 0, 0.01, 0.05, 0.1, 0.15 and 0.2) single crystals has been investigated upon fitting the Tb 3+ 5 D 4 luminescence decay curves with suitable mathematical equations. In the undoped TbAl 3 (BO 3 ) 4 compound, the Inokuti-Hirayama model properly fits the decay, so that the dominant 5 D 4 relaxation channel is the direct transfer of the excitation energy to the quenching impurity (Mo 3+ or other crystal defects) at short times after the excitation pulse. On the other hand, the transfer of the excitation energy to this quenching impurity through energy migration is negligible. As for the Eu 3+ doped samples, a generalization of the Parent et al. model has been employed. In this case, in the fitting equation the contribution of four different terms has been considered and calculated, one for each possible relaxation channel, that is: i ) the intrinsic Tb 3+ decay, ii ) the direct (not assisted by energy migration) Tb 3+ →Mo 3+ (or other crystal defects) energy transfer, iii ) the direct (not assisted by energy migration) Tb 3+ →Eu 3+ energy transfer and iv ) the Tb 3+ →Eu 3+ energy transfer assisted by energy migration in the Tb 3+ sublattice. From a semi-quantitative point of view, our investigation aligns with what has been qualitatively previously concluded on Tb 3+ →Eu 3+ energy transfer dynamics in TbAl 3 (BO 3 ) 4 , which would be ruled by an intermediate regime where the rate of the energy transfer among donors (Tb 3+ ) is comparable to the rate of the Tb 3+ →Eu 3+ energy transfer. More in detail, our study underlines the increasing impact of the term W on the 5 D 4 decay with the increase of the Eu 3+ concentration. This term is directly connected with the energy migration phenomenon involving the Tb 3+ subarray.