Amber Glass from Sugar Factory Sugarcane Leaf Ash Doped with Iron (III) Oxide

Abstract

This research aims to develop and investigate the influence of iron (III) oxide doping, at concentrations of 0.0 – 0.5 mol%, on the physical and optical properties of glass prepared from sugar factory sugarcane leaf ash. Sugarcane leaf ash, primarily composed of SiO2 and CaO at approximately 66.77% and 17.26% by weight, respectively, was utilized as a precursor to replace SiO2 and CaO in the glass formulation. The glass samples were melted using an electric furnace at 1,200°C and formed via a rapid quenching technique. The results indicated that as Fe2O3 concentration increased, the density and refractive index of the glass showed a continuous upward trend, ranging from 2.8756 – 2.8846 g/cm3 and 1.5703 – 1.5761, respectively. This is due to the high molecular weight of Fe2O3 and its effect on the atomic polarizability of the glass structure. Meanwhile, the increase in molar volume reflects the expansion of the glass network structure (network expansion) resulting from the increase of non-bridging oxygens (NBOs). Regarding optical properties, the absorption spectra exhibited a peak at a wavelength of approximately 1,050 nm, caused by the electronic transition from the 5T2g ground state to the 5Eg excited state of Fe2+ ions. This caused the glass to change from transparent and colorless to a brownish-yellow color, which intensified with increasing dopant concentration. Color analysis in the CIE L*a*b* system revealed that glass doped with 0.1 mol% Fe2O3 had color coordinates (L* = 78.23, a* = -5.63, b* = 15.11) similar to the color of natural amber based on the International Gem Society (IGS) database. This research confirms the potential of sugarcane leaf ash for development into synthetic gemstones and optical filter materials to add value to agricultural waste.