Enhanced structural and optical properties of sodium phosphate glasses with chromium chloride for optoelectronic and photonic applications

Abstract

This study reports the synthesis of a binary sodium phosphate glass system with the composition (50−x)Na₂O–50P₂O₅–xCrCl₃ (x = 0–9 mol%) produced via the melt quenching technique. The resulting glasses were characterized using various analytical techniques. X‑ray diffraction (XRD) confirmed the amorphous nature of samples containing up to 6 mol% CrCl₃, as evidenced by a broad diffraction halo between 20 and 30°. At higher CrCl₃ concentrations, partial crystallinity was observed. Fourier-transform infrared (FTIR) spectroscopy indicated a gradual increase in bridging oxygen content, suggesting enhanced polymerization within the phosphate network. Substituting Na₂O with CrCl₃ led to an increase in the density, molar volume, and packing density, accompanied by a reduction in the free volume. UV-visible spectroscopy revealed two prominent absorption bands near 470 and 650 nm, attributed to Cr³⁺ ions in distorted octahedral coordination. A weak band near 300 nm, associated with Cr⁶⁺ ions, was detected only in samples with lower CrCl₃ concentrations. The optical band gap decreased from 3.5 to 2.8 eV (indirect transition) and from 4.04 to 3.0 eV (direct transition), while the refractive index increased from 2.214 to 2.371 with CrCl₃ addition up to 9 mol%. These results demonstrate that incorporating CrCl₃ enhances the structural, physical, and optical properties of the glasses, underscoring their potential for optoelectronic and photonic applications.