## 2 Materials and Methods
### Optical Properties  
#### 2.3.1 UV-Vis-NIR Absorption Spectra  
UV-Vis spectrophotometer for reflective spectroscopy (RSA) (Lambda 35 Perkin Elmer, MA, USA) was used to estimate the absorption spectra of the glass samples within wavelength ranges of 200-2600 nm. Using absorption, the energy gap (\(E_{g}\)) can be obtained by applying the [PERSON] and [PERSON] relation  
\[(\alpha h\
u)=A\left(h\
u-E_{g}\right)^{n}/\left(h\
u\right) \tag{9}\]  
where \(\alpha\) is coefficient of optical absorption, \(A\) is a constant, \(\left(h\
u\right)\) is the incident photon energy, and \(E_{g}\) is the indirect permitted optical band gap energy. The direct \(E_{g}\) value is obtained from the plot \(\left(\alpha h\
u\right)^{1/2}\), and \(h\
u\) by extrapolating the linear-compatible regions to the value \(\left(\alpha h\
u\right)^{1/2}\)= 0 [16]. Urbach energy (\(E_{u}\)) offers knowledge about glass disorder. This \(E_{u}\) can be measured by using the relation [8]  
\[\alpha(\
u)=c.\exp^{\left(h\
u/E_{u}\right)} \tag{10}\]  
where \(c\) is constant and \(E_{u}\) is Urbach energy. The oscillator strength \(\left(f_{\mathrm{exp}}\right)\) of glasses can be determined using the next equation  
\[f_{\mathrm{exp}}=4.32*10^{-9}\int\varepsilon(\
u)d\
u \tag{11}\]  
where \(\varepsilon(\
u)\) is the coefficient of molar the absorption of the each band at an energy of \(\
u\)(cm\({}^{-1}\)) [17; 18; 19]. The refractive index (\(n\)) for the electronic polarization of ions and the local field of materials is among the most important optically dependent material parameters. The next relation can be used to define the refractive index (\(n\))  
\[\frac{\left(n^{2}-1\right)}{\left(n^{2}+2\right)}=1-\frac{\sqrt{E_{g}}}{20} \tag{12}\]  
Reflective loss on the surface of the glass is determined by using the refractive index of the Fresnel formula  
\[R_{L}=\left(\frac{\left(n-1\right)}{\left(n+1\right)}\right)^{2} \tag{13}\]  
Using the Volf and Lorentz-Lorenz formula, the molar refraction (\(R_{m}\)) for all samples was measured [20; 21]  
\[R_{m}=\left(\frac{\left(n^{2}-1\right)}{\left(n^{2}+2\right)}\right)\star V_{m} \tag{14}\]  
Molar refractivity (\(R_{M}\)) can be acquired using the following equation [22]  
\[R_{m}=\frac{\left(n^{2}-1\right)}{\left(n^{2}+2\right)}*\left(\frac{M}{\rho}\right) \tag{15}\]  
The following relation can be used to estimate molar polarizability (\(\alpha_{m}\)) [23]  
\[\alpha_{m}=\left(\
icefrac{{3}}{{4\pi N_{A}}}\right)*R_{m} \tag{16}\]Metallisation criterion is the prediction of the metal or isolating behaviour of the condensed matter and is determined using the following relation [24]  
\[M=1-\left(\frac{R_{m}}{V_{m}}\right) \tag{17}\]  
The materials are considered metallic when \(R_{m}/V_{m}>1\), and they are considered insulating when \(R_{m}/V_{m}<1\). Further, the polarizability of electrons (\(\alpha_{o}\)) and optical basicity (\(\Lambda\)) linked electronegativity (\(\chi\)) can be obtained by [25]  
\[\chi=0.2688E_{g} \tag{18}\]  
where (\(E_{g}\)) is optical band gap. The electronic polarizability is given by  
\[\alpha_{o}=-0.9\chi+3.5 \tag{19}\]  
The relation between the electronic oxide polarizability and optical basicity is described by [26].  
\[\Lambda=1.67(1-\frac{1}{\alpha_{2-}}) \tag{20}\]  
The dielectric constant (\(\varepsilon\)) and optical dielectric constant can be calculated using the following formulae [8]. The dielectric constant has calculated using refractive index of the glass  
\[\varepsilon=n^{2} \tag{21}\]  
where (\(n\)) is the refractive index. The optical dielectric constant of the glass calculated by the following relation  
\[p\frac{dt}{dp}=(\varepsilon-1)=n^{2}-1 \tag{22}\]  
where \(\varepsilon\) is the dielectric constant.