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In this study, investigation on photoluminescence and optical properties of europium doped zinc silicate (Zn2SiO4:Eu3+) glass ceramics derived from white rice husk ash as potential silica source have been done. Undoped and 3 wt. % of europium doped zinc silicate were prepared by solid state method and sintered at 600-1000 °C for 2 h. XRD analysis revealed the phase formation of amorphous, α or β-Zn2SiO4:Eu3+ phases of the glass and glass ceramic samples. FESEM results show the samples were irregular in shapes but well connected and formed large grain crystallites as sintering temperatures increases. The optical band gap values for undoped samples are increasing from 2.97 eV to 3.39 eV respectively. Meanwhile, the optical band gap values for 3 wt. % Eu3+ doped samples decrease from 4.14 eV to 2.62 eV and increase again to 3.71 eV as sintering temperature increases. PL analysis concludes that the red emission exhibited corresponding to 5D0 → 7F2 electron configuration at 612 nm while excitation spectra was found at 400 nm attributed to 7F0 → 5L6 transition. As conclusion, Eu3+ doped Zn2SiO4 glasses has potential as glass host phosphor which can be used for optical devices such as plasma display panels (PDPs) and cathode ray tubes.

The green synthesis of silica has been extensively explored over the last few decades, as silica compounds found in commercial products can cause negative effects on human health. This calls for alternative ways to produce silica that are safer, cheaper and more environmentally friendly. Some of the agricultural wastes proven to contain silica include rice husk, sugarcane bagasse, coconut shells and coconut husk. This paper describes the synthesis of silica from coconut husk waste, and its physical and optical properties for potential utilization in optical applications. Coconut husk was subjected to fire at 500–700 °C so as to form coconut husk ash (CHA), and was then treated with sulfuric acid to extract silica from the ash. Most of the weight degradation subsequently occurred at temperatures from 221 to 360 °C. X-ray fluorescence (XRF) analysis proved that 91.76% of the silica was obtained, while major peaks on the X-ray diffraction (XRD) spectrum were observed after the acid treatment. Chemical bonds such as Si-O-Si, CH2, -OH and Si-OH were found in the spectrum of the Fourier transform infrared spectroscopy (FTIR). Furthermore, the particles displayed rod-like shapes and irregular sizes, but the particle with sizes ranging from 200–750 nm decreased after the acid treatment. The relationship between the absorption coefficient and photon energy was obtained by finding the optical energy gap, which was found to be 4.3 eV. These data points provide critical information when used in optical applications. The overall studies show that synthesized silica has great potential for use in optical field applications.

In this work, waste coconut husk ash was used to prepare a ZnO-SiO2 composite. Solid-state technique was used to fabricate the composite due to its producibility, simple procedure as well as lower production cost. At high sintering temperatures ranging from 600 °C to 1000 °C, the X-ray diffraction (XRD) peaks of the Zn2SiO4 showed high intensity, which indicated high crystallinity. Furthermore, the formation of broad bands of ZnO4, Si-O-Si, and SiO4 were detected by Fourier transform infrared (FTIR) spectroscopy and the bands became narrower with the increment of sintering temperature. Besides, the morphological image from field emission scanning electron microscopy (FESEM) showed the formation of densely packed grains and smooth surface composite with the increase of sintering temperature. Upon obtaining the absorbance spectrum from Ultraviolet–Visible (UV–Vis) spectroscopy, the optical band gap was calculated to be 4.05 eV at 1000 °C. The correlation between the structural and optical properties of ZnO-SiO2 composite was discussed in detail.

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