## 3 Results
### UV-Vis Analysis  
Ultraviolet range studies are very important, as they provide scientific information to understand a specific material's electronic band gap. In the higher wavelength region, optical absorbance is small, a comparison to the lower wavelength region will produce higher absorbance intensity due to ultraviolet \"cut off\" that emerges as a term to identify the factor for progress in the absorption energy [31; 32]. From previous studies, it is found that a clear intensive absorption generated within the range 250-400 nm is mostly from its absorption curve in the glass and glass-ceramic systems [33]. Figure 4 displays the optical absorption UV-Vis spectra of the sample at different heat-treatment temperatures. Rapid rises in the absorbance toward lower wavelengths are present in the optical absorption spectrum of glass material. This rapid rise of absorption coefficient can be referred to as the fundamental absorption edge known as UV cut off. It was clear that there was no sharp absorption edge after the glass sample was heat-treated at 600 \({}^{\circ}\)C, which corresponds to the characteristic of the glassy state observed [34]. There was also a sharp absorption edge at 700 \({}^{\circ}\)C, and it disappeared after the sample was heated to a higher temperature (800 \({}^{\circ}\)C). This indicates that as the formation of zinc silicate crystal occurred, a few ZnO particles were left in the sample at 700 \({}^{\circ}\)C, but at 800 and 900 \({}^{\circ}\)C, all ZnO was used for the formation of zinc silicate crystal. This is consistent with the previous research [35; 36]. Moreover, the heat-treated sample intensities decreased from 600 to 900 \({}^{\circ}\)C because of the fall of the hexagonal ZnO structure and the formation of a zinc silicate structure [37]. Meanwhile, as heat-treatment temperature increased, the absorption edge shifted back to a shorter  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Wavenumber (cm\({}^{-1}\))** & **Assigned of Vibration Modes** \\ \hline
457 & Asymmetric deformation of SiO\({}_{4}\) \\
570 & Symmetric stretching of ZnO\({}_{4}\) \\
611 & Asymmetric stretching of ZnO\({}_{4}\) \\
710 & Si-O bond vibration \\
866 & Symmetric stretching of SiO\({}_{4}\) \\
900, 930, 977 & Asymmetric stretching of SiO\({}_{4}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: FTIR transmittance bands associated with assigned vibration modes.  
Figure 3: Fourier transform infrared reflection (FTIR) pattern of 55 ZnO–5B\({}_{2}\)O\({}_{3}\)–40 SLS glass and glass-ceramic sample at various heat-treatment temperatures.  
wavelength. This can be due to the high crystallinity induced by the phase formation of zinc silicate crystal. To obtain the value of the energy band gap, the graph of (\(\alpha\)uv)\({}^{1/n}\) vs. _lvv_ was plotted and the slope intercept of the line obtained is equal to the optical transition of band gap energy. This \(n\) can have various values such as 1/2, 1/3, 2 and 3; these values correspond to direct allowed, direct forbidden transitions, indirect allowed, and indirect forbidden transitions, respectively. The study of [PERSON] et al. (2016) observed that the optical band gap decreases due to the direct forbidden transitions [38]. Thus, in this experiment \(n\) = 2/3 (direct forbidden transition) was used to find the value of the band gap energy of the sample. Figure 5 and Table 3 show the optical band gap (E\({}_{\text{opt}}\)) values for glass and glass-ceramic samples heat treated at various temperatures. It is found that with the rise in temperature of heat treatment, the value of E\({}_{\text{opt}}\) of the glass-ceramic sample decreased from 3.867 to 3.423 units. This decline in the optical band gap resulted from shorter wavelength light having been scattered by the zinc silicate crystal as the crystallinity increased at higher heat-treatment temperature [39]. Furthermore, the progress in NBOs formation led to the defects in the bands, which is another potential reason for the decline in the optical band gap [40].