Synthesis and characterization of low cost willemite based glass–ceramic for opto-electronic applications

This paper presents a comprehensive study on thermal, structural and optical properties of novel willemite glass–ceramics. The precursor glass in the ZnO–SLS glass system was successfully prepared using conventional melt-quenching technique and willemite (Zn₂SiO₄) glass–ceramics were derived from this precursor glass by a control crystallization process. The effect of heat-treatment temperature on the phase transformation, morphology and size of Zn₂SiO₄ crystal phase was examined using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) techniques. Furthermore, fourier transform infrared reflection (FTIR) spectroscopy was used to evaluate the Zn₂SiO₄ crystal structural evolution. The average size of Zn₂SiO₄ crystallite obtained from calculation of XRD is found to be in the range 30–60 nm, whereas the grain size observed in FESEM is in range of 200–400 nm. The appearance of SiO₂, ZnO₄ and Zn–O–Si bands detected from FTIR indicate the formation of Zn₂SiO₄ crystal phase. Besides, the study of the optical band gap has found that optical band gap of the glass–ceramics decreased as the heat treatment temperature increased. The photoluminescence spectra of willemite glass–ceramics exhibit two different emissions around 525 nm (green) and 585 nm (yellow); exhibit a characteristic of broad absorption band around 260 nm. These two different spectra reveal that the luminescence performance of the willemite glass–ceramics was enhanced with the progression of heat treatment temperature due to different located energy levels of the β-Zn₂SiO₄ and α-Zn₂SiO₄ crystalline phase. Such luminescent glass–ceramics was expected to find potential applications in phosphors and opto-electronic devices.