Dopant Concentration Dependence of Structural and Optical Properties in Lead Silicate Glasses Doped with Nickel, Cobalt and Chromium

Reference	Presenter	Authors (Institution)	Abstract
10-074	Rafaella Bartz Pena	Pena, R.B.(Federal University of São Carlos (UFSCar)); Sampaio, D.V.(Federal University of São Carlos (UFSCar)); Moulton, B.J.(Federal University of São Carlos (UFSCar)); Pizani, P.S.(Federal University of São Carlos (UFSCar)); Zanotto, E.D.(Federal University of São Carlos (UFSCar));	Lead silicate glasses are particularly interesting, once lead is the only element that associated to silica, can form glasses over a large range of compositions. Moreover, under normal atmospheric conditions, these glasses are aimed to favor 3d transition metal ions in its highest valence state or tetrahedral coordination state. However, it is not reported in the literature the optical and structural dependence of these glasses with the dopant concentration. Therefore, this work focused on investigating UV-Vis absorption and Raman spectra of lead silicate glasses doped with nickel, cobalt and chromium ions over a range of 0.25mol% to 12.5mol% in partial substitution to the lead. The obtained UV-Vis spectra agreed with results showed in the literature for similar systems. Considering the concentration increasing effect, on the one hand, the bandgap energy decreased, varying greatly for chromium, intermediately for cobalt and subtly for nickel. On the other hand, Urbach energy increased, indicating a gradual induction of structural defects within the glass. Considering the Raman spectra, the high frequency region (800-1200 $c{m}^{-1}$) was analyzed qualitatively, which might indicate any structural modification in relation to the pure lead silicate. In this region, the nickel and cobalt doped glasses did not show any change until 4 mol%. However, the chromium doped glasses showed an additional peak centered at 830$c{m}^{-1}$ even for the 0.25mol% doped sample. This peak was assigned to the $C{r}^{6+}$present in a tetrahedral environment as ${\mathrm{CrO}}_4^{2-}$. Above 4mol%, the doped glasses showed some changes in the high frequency region due to structural modifications. The chromium samples segregated ${\mathrm{Cr}}_2{0}_3$ for these higher concentrations, while the other dopants did not show any segregation until 12.5mol%. These results suggest that the dopants studied acted as network modifiers over concentrations higher than 4mol%, corroborating that lead silicate is a stable host glass structure.
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