Optical Investigation of Eu3+ in a Sodium Borosilicate Glass: Evidence for two Different Site Distributions

A borosilicate glass of molar composition 0.01Eu2O3·0.99(25Na2O·50B 2O3·25SiO2) has been studied through the optical spectroscopy of the Eu3+ ion. Absorption and excitation spectra, fluorescence line narrowing, and time-resolved spectroscopy show that the impurity ions are accommodated in two different site distributions, one related to a silicate environment, and the other one related to a borate environment. These results have been corroborated by crystal-field calculations and comparison with the crystal-field parameters for the Eu3+ ion in silicate and borate glasses. The presence of phonon sidebands indicates strong coupling with high-frequency Si-O and B-O stretching vibrational modes.