Unlocking the secrets of colored glass: Structural-optical behaviors and non-linear optical properties of La3+ and Fe3+ ions-doped borates

Investigations of structural-optical properties were performed for La3+-doped borate glass host based on a fixed ratio of Fe3+ ions, and within a lanthanum oxide concentration range of (0-8 mol%). The density was measured and confirmed the increase in bond density of the network, with increasing its volume. While infrared spectroscopy was carried out to investigate the dominant role of lanthanum on structural variations of glass, for example, the BO3 to BO4 conversion and the conspicuous decrease in NBO content. Optically, the d-d visible transitions of Fe3+ ions were suppressed by La3+ quenchers, preventing their peaking within the optical absorption spectra of glass samples. Further, in good coalescence with density and infrared spectroscopy results, Tauc gap energy increased with lanthanum oxide addition owing to the band structure modulations. Additionally, the metallization criterion changed from 0.262 (eV)(0.5) to 0.325 (eV)(0.5), owing to the Tauc gap energy increment, indicating that the lanthanum addition causes a shift toward the semiconducting nature of the prepared samples. On the other hand, Urbach energy decreased with increasing lanthanum oxide content, manifesting the glass structure's propensity toward less disorder and high polymerization. Besides, the increase in electron-phonon interaction energy indicates a high possibility of phonon consumption to bind free electrons as pairs, mitigating the network disorder. Surprisingly, the non-linear optical properties of the glass matrix were enhanced through lanthanum oxide addition. For the current glass host activated by La3+ ions, including Fe3+ color centers, the correlation between these above-mentioned structural modifications, and optical findings provide a decent paradigm for the optics realm.