OPTICAL SPECTROSCOPY OF EU3-GELS( ION AS A TOOL FOR THE STUDY OF DEHYDRATION PROCESS IN SILICA)

The structural modification induced by dehydration in optical silica g el has been studied using the spectroscopy of Eu3+ ion. The samples, d oped with molar ratio Eu/Si = 0.01:1, were heated for 48 hours at diff erent temperatures from 60-degrees-C to 200-degrees-C. Information on the dinamical properties of the local environment of the Eu3+ were obt ained both by fluorescence and excitation measurements at T = 11 K. Th e analysis of the 5D0 --> F-7(0) transition appears of particular rele vance in this study, because the transition is between J = 0 states an d does not present internal structure. Its inhomogeneous linewidth giv es a measure of the energy distribution of the different Eu3+ sites. S ite selection spectroscopy was performed by exciting into the 5D1 stat e. Three different sets of sites were found, The phonon sidebands of t he 5D0 <-- F0 and 5D1 <-- F-7(0) transitions were observed in the exci tation spectra.