## 3 Results and Discussion
As Na\({}_{2}\)CO\({}_{3}\) dopant concentration increased up to 5 wt%, the T\({}_{\text{g}}\) and T\({}_{\text{x}}\) decreased from 380 to 360 \({}^{\circ}\)C, and 510 to 480 \({}^{\circ}\)C, respectively. The \(\Delta\)T remained almost unchanged regardless of Na\({}_{2}\)CO\({}_{3}\) dopant concentration. The higher the value of \(\Delta\)T, the greater the delay in the nucleation process, the greater the thermal stability, and the easier the glass formation [23]. A similar effect was observed in sodium silicate glasses and borate glasses when Na\({}_{2}\)O was added to the glass [22, 24]. The constant of \(\Delta\)T regardless of Na\({}_{2}\)CO\({}_{3}\) dopant concentration indicated that there was no big difference in the nucleation process. Therefore, it was thought that the decrease of T\({}_{\text{g}}\) in this work was mainly due to the formation of nonbridging oxygens. It was aforementioned that the CTE between 1 wt% CuO doped PSAB glass and the FTO coated glass panel was in the order of \(2\times 10^{-6}\)/K. In order for the CTE difference to be below \(1\times 10^{-6}\)/K, the PSAB glass system was codoped with 1.0 wt% CuO, and Na\({}_{2}\)CO\({}_{3}\) concentration varied from 0 wt% to 2.5 wt%. Figure 4a shows the TMA profiles of codoped PSAB glass system as a function of Na\({}_{2}\)CO\({}_{3}\) concentration. The inset of Figure 4a presents that increasing Na\({}_{2}\)CO\({}_{3}\) concentration up to 2.5 wt% results in a decrease of T\({}_{\text{g}}\) from 395 to 375 \({}^{\circ}\)C. The CTE of the codoped PSAB glass system as a function of Na\({}_{2}\)CO\({}_{3}\) dopant concentration for different temperature ranges is shown in Figure 4b. It was noticed that the CTE increased from \(8.10\times 10^{-6}\)/K to \(9.31\times 10^{-6}\)/K, \(8.45\times 10^{-6}\)/K to \(9.61\times 10^{-6}\)/K, and \(8.90\times 10^{-6}\)/K to \(9.89\times 10^{-6}\)/K for the temperature ranges of 25-100 \({}^{\circ}\)C, 25-200 \({}^{\circ}\)C, and 25-300 \({}^{\circ}\)C, respectively. In the case of the codoped PSAB system, the T\({}_{\text{g}}\) decreased and the CTE increased with increasing Na\({}_{2}\)CO\({}_{3}\) dopant concentration. The difference of CTE was found to be low of the order of \(0.34\times 10^{-6}\)/K between the FTO coated glass panel (\(10.23\times 10^{-6}\)/K) and 1 wt% CuO-2 wt% Na\({}_{2}\)CO\({}_{3}\) codoped PSAB glass system (\(9.89\times 10^{-6}\)/K). The major reason for the decrease of CTE difference in the codoped PSAB glass system may be due to Na\({}_{2}\)CO\({}_{3}\) concentration that was not attributed to the fact that the adding of Na\({}_{2}\)CO\({}_{3}\) in the silicate network provides nonbridging oxygens and thus decreases the T\({}_{\text{g}}\), as explained in Figure 3.  
In order to investigate the absorption at 810 nm, the transmission spectra of CuO-singly doped and CuO-Na\({}_{2}\)CO\({}_{3}\) codoped PSAB glasses are shown in Figure 5. Figure 5a presents the transmittance spectra of CuO-doped PSAB glasses in the region 300-1100 nm for different concentrations of CuO. From the spectra, the bands at 500 and 810 nm are assigned to the Cu\({}^{2+}\) transitions of 3d\({}^{10}\)\(\rightarrow\) 3d\({}^{9}\) 4s\({}^{1}\) and \({}^{2}\)B\({}_{1g}\)\(\rightarrow\)\({}^{2}\)B\({}_{2g}\), respectively [25; 26]. In the base PSAB glass system, the average transmittance between 500 and 1100 nm was about 70%. As CuO concentration increased, the transmittance decreased because of the UV absorption edge. The transmittance at 810 nm for 0.2 wt% and 0.5 wt% CuO-doped PSAB glasses was found to be 20.7% and 3.19%, respectively. For 1 wt% CuO, the transmittance was not observed at 810 nm. This result revealed that the absorption intensity and broadening at 810 nm increased with increasing CuO concentration.