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 Tb3+ ion in samples of trigonal huntite-type Tb1-xEuxAl3(BO3)4 (with x = 0, 0.01, 0.05, 0.1, 0.15 and 0.2) single crystals has been investigated upon fitting the Tb3+ 5D4 luminescence decay curves with suitable mathematical equations. In the undoped TbAl3(BO3)4 compound, the Inokuti-Hirayama model properly fits the decay, so that the dominant 5D4 relaxation channel is the direct transfer of the excitation energy to the quenching impurity (Mo3+ 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 Eu3+ 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 Tb3+ decay, ii) the direct (not assisted by energy migration) Tb3+-> Mo3+ (or other crystal defects) energy transfer, iii) the direct (not assisted by energy migration) Tb3+-> Eu3+energy transfer and iv) the Tb3+-> Eu3+ energy transfer assisted by energy migration in the Tb3+ sublattice. From a semi-quantitative point of view, our investigation aligns with what has been qualitatively previously concluded on Tb3+-> Eu3+ energy transfer dynamics in TbAl3(BO3)4, which would be ruled by an intermediate regime where the rate of the energy transfer among donors (Tb3+) is comparable to the rate of the Tb3+-> Eu3+ energy transfer. More in detail, our study underlines the increasing impact of the term W on the 5D4 decay with the increase of the Eu3+ concentration. This term is directly connected with the energy migration phenomenon involving the Tb3+ subarray.