Structural and optical tuning of methyl orange-doped 45S5 glass via sol–gel synthesis: implications for optoelectronic applications

Organic–inorganic hybrid glasses provide an attractive platform for tailoring optical properties through the controlled incorporation of functional organic molecules. In this study, methyl orange (MO)-doped 45S5 silicate–phosphate glasses containing (0.02, 0.04, 0.06, and 0.08 wt. %) MO were synthesized via a low-temperature sol–gel route, and the effects of MO incorporation on their structural, morphological, compositional, and optical properties were systematically investigated. X-ray diffraction revealed variations in the relative amorphous and crystalline contributions of the glass matrix, accompanied by the appearance of a calcite (CaCO 3 ) phase in the MO-containing samples. FTIR spectroscopy revealed changes in the vibrational features of the silicate–phosphate network following MO incorporation, while SEM-EDX and elemental mapping provided complementary evidence for microstructural densification and the presence and spatial distribution of MO-associated elements within the analyzed regions. UV–Vis diffuse reflectance spectroscopy combined with the Kubelka–Munk approach revealed pronounced changes in the optical response of the doped samples. The optical band-gap energies estimated using Tauc analysis decreased from 5.86 to 4.82 eV for allowed direct transitions and from 5.54 to 4.18 eV for allowed indirect transitions with increasing MO concentration. The optical conductivity also exhibited systematic changes following MO incorporation. Photoluminescence measurements showed a gradual decrease in emission intensity with increasing MO concentration, while the main emission features remained at comparable spectral positions. Overall, the results demonstrate that methyl orange can effectively modify the structural and optical response of sol–gel-derived 45S5 glass, highlighting its potential for optical and optoelectronic applications.