Fe-dependent optical properties of peralkaline soda aluminosilicate glasses: a combined Raman and photoluminescence study

This study investigates the influence of iron on the optical properties of peralkaline soda aluminosilicate glasses (NASF), focusing on the interplay between glass structure and optical behavior. Fe doping significantly affects the glass network, altering both its structural connectivity and optical properties. Raman spectroscopy reveals that Fe modifies the glass structure by increasing non-bridging oxygens (NBOs), reducing network connectivity. For the highest FeO tot concentration of 8.2 at.%, a more polymerized structural reorganization occurs due to iron self-compensation. Optical analysis shows that Fe incorporation increases the optical absorption and shifts the absorption edge to higher wavelengths. Tauc plot calculations reveal a decrease in the optical bandgap from 4.0 to 3.2 eV, while the Urbach energy indicates an increase of structural disorder. The photoluminescence (PL) excitation and emission related to Fe 3+ energy levels is observed, with a broad red emission peak at 700 nm, decreasing with Fe concentration in relation to higher defectivity and clustering. A detailed lifetime analysis shows long lasting tails of the order of milliseconds, also decreasing with Fe content due to non-radiative recombinations and quenching.