Spectroscopic investigation of zinc borate glasses doped with trivalent europium ions

4ZnO · 3B2O3 glasses undoped and doped with 0.5-2.5% Eu3+ were studied using absorption, emission and excitation spectroscopies, fluorescence line narrowing, Raman scattering and lifetime measurements. The vibrational spectra of the undoped and doped glasses are very similar and indicate the presence of borate groups already observed in binary metaborate glasses. The Judd-Ofelt parameters and the asymmetry ratio derived from the f-f transitions of the Eu3+ ion give information on the average local structure around the impurity ions. Crystal-field parameters obtained from site selective emission spectra are close to those found for various silicate glasses, and their major ratios are close to predictions of the Brecher and Riseberg model. A very strong phonon sideband is coupled to the 5D0 <- 7F0 transition; a value of 0.11 is obtained for the electron-phonon coupling strength. Comparison with Raman spectra indicates that the sideband is due to an Eu3+-O stretching/BO3 3- mode. No energy transfer is found in the most diluted samples.