Electronic excitation energy transfer processes in Er:YAG under variable pump duration

For the first time, the luminescence decay dependences of 4I13/2 and 4I11/2 energy levels on pulsed excitation duration are studied with and without pinhole technique in erbium-doped YAG single crystals. Luminescence decay investigations of 4I13/2 → 4I15/2 (1565 nm) and 4I11/2 → 4I15/2 (970 nm) transitions are carried out on 5 at.% and 40 at.% doped samples. Time-resolved measurements of luminescence decay have demonstrated non-exponential behavior depending on excitation duration as well as impurity concentration, thus, indicating the presence of various energy transfer processes. In order to eliminate the influence of radiation trapping effect on luminescence decay from 4I13/2 and 4I11/2 levels the pinhole technique is used. Qualitative comparisons of luminescence decay curves are made to estimate the influence of radiation trapping effect. The influence of non-radiative energy transfer processes on population redistribution of 4I13/2 and 4I11/2 energy levels is evaluated. A theoretical model for non-radiative transfer of electronic excitation energy in YAG:Er3+ crystals is proposed, in the frame of which the constants of rate equations are determined. The experimental and theoretical investigations are made for luminescence corresponding to both 4I13/2 → 4I15/2 and 4I11/2 → 4I15/2 transitions. The following non-radiative energy transfer processes are taken into account: 4I13/2 → 4I15/2 + 4I13/2 → 4I9/2, 4I11/2 → 4I15/2 + 4I11/2 → 4F7/2, 4S3/2(2H11/2)→4I9/2 + 4I15/2 → 4I13/2, 4I11/2 → 4I15/2 + 4I13/2 → 4F9/2.