Luminescence spectroscopy of europium(III)-doped silica gels and silicate glasses

Local structure and bonding of rare earth ions in amorphous silica have been examined using Eu{dollar}sp{lcub}3+{rcub}{dollar} luminescence spectroscopy. Rare earth ion-doped silica gels and glasses are of interest for their optical device applications, including solid state lasers and fiber amplifiers. An understanding of rare earth ion-silica interactions is also relevant from a geological perspective. Eu{dollar}sp{lcub}3+{rcub}{dollar} was selected as a representative rare earth ion because its unique luminescence properties make it particularly amenable to interpretation of local structure and bonding.; Eu{dollar}sp{lcub}3+{rcub}{dollar} luminescence spectroscopy was used to characterize local bonding evolution during the sol-gel synthesis of doped silica gels and glasses. Luminescence spectra and lifetime data suggested that Eu{dollar}sp{lcub}3+{rcub}{dollar} ions have only weak interactions with the silica gel matrix prior to thermal densification. Dopant ions remained dissolved in pore liquid prior to densification, and the optical properties of the material were determined by the counter-ions of the rare earth salts and the composition of the pore solution. Upon densification, significant rare earth ion clustering occurred in Eu{dollar}sp{lcub}3+{rcub}{dollar}-doped silica, even at Eu{dollar}sp{lcub}3+{rcub}{dollar} concentrations as low as 0.5 wt.%. Clustered Eu{dollar}sp{lcub}3+{rcub}{dollar} ions were identified by the lack of a fluorescence line narrowing effect, which is interpreted as a result of efficient Eu{dollar}sp{lcub}3+{rcub}{dollar}-Eu{dollar}sp{lcub}3+{rcub}{dollar} energy transfer in the clusters. Co-doping the silica matrix with Al{dollar}sp{lcub}3+{rcub}{dollar} was effective at dispersing and isolating Eu{dollar}sp{lcub}3+{rcub}{dollar} ions. Fluorescence line narrowing studies showed that Eu{dollar}sp{lcub}3+{rcub}{dollar} ions preferentially interact with the more ionic Al{dollar}sp{lcub}3+{rcub}{dollar} groups in the matrix.; Eu{dollar}sp{lcub}3+{rcub}{dollar}-doped sodium disilicate glass was also investigated at high pressure using diamond anvil cell technology. High pressure fluorescence line narrowing (HPFLN) spectroscopy was demonstrated as an analytical tool. Increasing pressure to 40 kbar led to a slight decrease of the crystal field strength and a lengthening of the fluorescence lifetimes. Above 40 kbar, field strengths increased and lifetimes decreased. HPFLN results are interpreted in terms of crystal field theory, changes in local structure, and electron-phonon coupling in the glass.