Effect of silver iodide (AgI) on structural and optical properties of cobalt doped lead-borate glasses

Abstract Materials with distinct optical characteristics are still being explored. Hence, AgI doped cobalt-lead borate glasses of composition [29.7PbO – 0.3CoO – (70-x) B2O3 – xAgI (x = 0.0, 0.25, 0.5 and 1.0 mol%)] were synthesized via conventional melt quenching technique. XRD patterns and SEM micrographs confirmed the prepared glass system's amorphous nature; EDAX elemental analysis was also performed. According to increased density and decreased average boron-boron separation, AgI additives were found to enforce the glassy network's compactness. FT-IR analysis indicates the entry of AgI as a network modifier by converting the tetrahedral (BO4) to trigonal (BO3) units with NBO's ratio growth. The Raman data accords with FT-IR results and provides complementary information around these glasses by detecting additional structural groups. The ellipsometer spectroscopy technique confirmed the ability to control the refractive index of the current glassy system with the AgI addition. The absorption spectra clarified a gradual enhancement of Co3+/Co2+ ions at tetrahedral and/or octahedral sites by AgI additives. Ligand field parameters, such as crystal field intensity ( 10 D q ) and Racah parameters ( B & C ), were accurately determined. The calculated nephelauxetic ratio ( β ) indicated a reducing covalent nature among Co2+ ions and the nearby bonds. Calculations of the UV absorption edges showed a clear red-shift by AgI additives with a remarkable gradual reduction of the optical band gap. Besides, the Urbach energy increased, and the metallization criterion varied from 0.394 to 0.391 eV-1, reflecting the semiconductor character of these glasses. The spectral tunability for optical absorption provided here by AgI additives qualifies present glasses as optically active materials for several potential applications in multi-functional optical devices operating in the visible and near-infrared (NIR) spectral regimes.