## 3 Results and Discussion
We found that a heat treatment of the glass at 400 \({}^{\circ}\)C for 8 h, which corresponds to the annealing step in the glass melting process, is sufficient to erase the spot created by the irradiation but has no significant impact on the surface roughness. Further optimization of the heat treatment post irradiation is in progress to photo-bleach the irradiated glass. The UV-Vis-NIR transmittance and the reflectance in THz range, measured prior to and right after irradiation, are presented in Figure 4a,b, respectively. The transmittance in UV-Vis-NIR range decreases after irradiation, which is in agreement with the appearance of the visible spot. Similar decreases in the transmission after alpha particles irradiation were reported in different materials such as CaF\({}_{2}\), Al\({}_{2}\)O\({}_{3}\) or ZnSe due to the formation of color centers [9]. The absorption coefficients in the visible wavelength range of the Er\({}^{3+}\) 4f-4f transitions also decrease after irradiation indicating that the irradiation has a significant impact on the Er\({}^{3+}\) ions sites. As seen in Figure 4b, the alpha particle irradiation also produces a change of the THz frequency signal: no shift in the maximum was observed, but as seen in the case of Al\({}_{2}\)O\({}_{3}\) and ZnSe, only a decrease \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Ra (nm)** & **Rq (nm)** & **Rz (nm)** & **Rt (nm)** \\ \hline \multicolumn{4}{c}{**Prior to Heat Treatment**} & & \\ \hline Non-irradiated area & 38 & 46 & 431 & 505 \\ Irradiated spot measured 1.5 months after the irradiation & 219 & 250 & 1470 & 2640 \\ Irradiated spot measured 3 months after the irradiation & 121 & 154 & 621 & 642 \\ \hline \multicolumn{4}{c}{**After Heat Treatment at 400 \({}^{\circ}\)C for 8 h**} & & \\ \hline Non-irradiated area & 66 & 76 & 319 & 336 \\ Former irradiated spot & 162 & 191 & 897 & 926 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Surface roughness parameters of the glass surface measured after (1.5 and 3 months) irradiation and after heat treatment. Figure 3: Image of spots at the surface of the glass (**a**) and its surface profile (**b**) using Wyko NT1100 optical profiling system. of the amplitude can be noticed after irradiation. This can be related to the formation of defects or to structural deformations occurring during the irradiation. The micro-PL spectrum of the irradiated spot was measured 3 months after the irradiation. The spectrum was compared to the micro-PL spectrum collected from a non-irradiated area. The spectra are shown in Figure 5.  
The 3-month-old irradiated spot exhibits a slightly larger emission than the non-irradiated area of the glass. As seen in Figure 5b, the irradiation might also lead to small changes in the site of Er\({}^{3+}\) ions. As the irradiation took place in vacuum, hence poorer heat dissipation occurred in these samples produces local thermal stress. It is possible to think that the irradiation of the glass reduces the amount of OH groups, which are known to diminish the emission intensity by non-radiative phenomena [21]. Additional irradiation experiments using different doses are in progress to confirm the impact of the irradiation on the structure and luminescence properties of the glass.