Role of Er3+ concentration in high-resolution spectra of BaY2F8 single crystals

Fourier transform absorption spectroscopy with a resolution as fine as 0.02 cm(-1) was applied to Er3+-doped monoclinic BaY2F8 laser crystals in a wide wave number range (500-24 000 cm(-1)) and in the temperature range 9-300 K. The careful analysis of the complex narrow line spectra induced by Er3+ allowed us to determine with high accuracy the crystal field splitting of the fundamental I-4(15/2) and of the excited I-4(13/2), I-4(11/2), I-4(9/2), F-4(9/2), S-4(3/2), H-2(11/2), F-4(7/2), F-4(5/2), and F-4(3/2) manifolds. On the basis of the experimental data, the crystal-field parameters were determined and Newman's superposition model was applied: in this way a slight displacement of Er3+ with respect to the Y3+ position was foreseen. The Judd-Ofelt parameters were evaluated: the lifetime values deduced from them were compared to the experimental ones and discussed. The effects caused by increasing Er3+ concentrations (0.5%, 2%, 12%, and 20% atomic fraction) were studied in detail. The new lines, the line broadening, and the line-shape changes were explained in terms of Er3+-Er3+ interaction.