Fig. 5: Wet-chemistry-assisted redox state quantification in systems with three coexisting oxidation states.

a–c Calculated potentiometric curves considering model systems with varying initial proportions of vanadium species. The involved redox couples and their corresponding equivalence volumes are indicated. The ratio of the Ce⁴⁺ titrating solution to total vanadium concentration is 100. Deconvoluted optical absorption spectra of V-doped glasses synthesized d without a reducing agent (NaP-V), or e with a reducing agent (NaP-R-V). The determined molar extinction coefficients for V⁴⁺- and V³⁺-related electronic transitions are annotated. Photographs of the NaP-V and NaP-R-V samples are presented in the insets, highlighting the characteristic green color of V⁴⁺- and V³⁺-containing glasses².