Optical spectroscopy analysis of the Eu3+ ions local structure in calcium diborate glasses

A detailed analysis of the optical properties of EU3+ ions in calcium diborate glasses has been performed in order to correlate them with the local environment of the lanthanide ions in these glasses. From the excitation and emission spectra under broadband excitation the energy level diagram of the EU3+ ion and the atomic parameters have been obtained. Moreover, it is found that the Eu3+ ions are predominantly bonded with the bridging and non-bridging oxygens of different borate groups containing the BO3 units. Under site selective excitation in the F-7(0) --> D-5(0) inhomogeneously broadened peak, valuable information about the splitting of the F-7(1) and F-7(2), levels and the lifetime of the D-5(0) level has been obtained as a function of the excitation wavelength. The linewidth of the low-energy components of the D-5(0) --> F-7(1) emission shows an increase with the splitting of this level that can be well explained considering nonradiative de-excitation processes towards lower F-7(1) Stark levels. From the splitting of the F-7(1) and F-7(2) levels, the second and fourth rank crystal-field parameters have been calculated as a function of the excitation wavelength. The observed behaviour suggests the existence of an unique class of site for the Eu3+ ions, with a large range of values for the crystal-field strength parameter N-V(B-2q), from 1000 to 3200 cm(-1), that includes weak, medium and strong crystal-field environments for the Eu3+ ions in the calcium diborate glass. The J-mixing is shown to play a relevant role in these calculations for medium and strong crystal-field environments, i.e., for values of the crystal-field strength parameter N-V(B-2q) over 1400 cm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.