Features of sol-gel silica glasses after Gd-doping

Among the glassy systems, Ce-doped sol-gel silica glasses exhibit excellent scintillation properties [1]. Different rare earth ions were doped in a sol-gel silica glass to obtain new scintillation materials. In a previous research, some indications were obtained while comparing Ce and Gd-doped glasses [2]. A multidisciplinary study was performed on Gd-doped sol-gel silica glasses (in the range 0-8 Gd mol%). Raman spectroscopy did evidence the typical vibrational spectra of silica glasses (see figure 1), but no signal related to Gd2O3 crystal. On the other side, a Gd2O3 vibrational absorption at ~ 530 cm-1 was observed by IR-absorption. By transmission electron microscopy (TEM) no crystalline aggregates were detected within the amorphous matrix, up to 8 Gd mol%, though TEM analyses revealed amorphous clusters for Gd concentration higher than 1 mol%. Moreover, the size of nanoclusters increases by increasing the dopant concentration and by performing a rapid thermal treatment (RTT) procedure at 1800 °C in air (see figure 2). Electron Paramagnetic resonance was perfomed on alla samples in order to study the signal of Gd3+ ion, and indeed two different spectra are recorded before and after RTT (as displyed in figure 3). Finally, steady state and time resolved photoluminescence (PL) measurements were perfomed. We noted that samples before RTT displyed an higher PL intensity. Moreover, time resolved disclosed a radiative lifetime shortening after RTT treatment, as shown in figure 4. The results obtained with different techniques can thus suggest that RTT affects Gd dispersion in silica. In particular, EPR results indicate a better dispersion of Gd ions after RTT (since the width of the signals decreases), while the lifetime shortening can be explained by a concentration quenching effect, in a coherent way with the decrease of PL intensity after RTT.