Multiple optical features in binary-transition-metal borate glasses

Glasses doped with transition metal (TM) ions exhibit rich optical transitions spanning the entire ultraviolet, visible, and infrared spectral regimes. Here we utilize melt-quenching technique to synthesis binary-TM-doped alkali-borate glasses of composition xCuO-(75-x)B2O3-24.7Li2O-0.3Cr2O3, variable copper ion concentrations (x = 0, 0.2, 1.0 2.0 mol %) a fixed amount chromium (0.3 %). We identify several from Cr3+, Cr6+, Cu2+ ions, latter manifests exclusively at longer wavelengths gains noticeably higher intensity Cu additives. Despite Cr concentration being fixed, Cr6+ peaks are quenched Cr3+ signals barely attenuated. This behavior rules out possible phase separation suggests non-trivial interplay between two types TM their ligand, as supported by probing oxidation states electron spin resonance. The crystal field Racah parameters followed an opposite behavior, while band gap was reduced upon doping. These changes correlated structural modifications introduced additives, where anticipate homogenous preferential proximity Cu-Cr within network.