## 2 Experimental Section  
For the purpose of silver and europium doping, three basic types of bismuth-borate glass matrices were proposed, with B\({}_{2}\)O\({}_{3}\)-Bi\({}_{2}\)O\({}_{3}\) molar ratios of 50:50 (BBO(50:50)), 60:40 (BBO(60:40)) and 70:50 (BBO(70:30)). To such compositions, 1 mol% Ag and 0.5 mol% Eu\({}_{2}\)O\({}_{3}\) (relative to the total composition of Bi and B) were added. The nominal compositions are reported in Table 1. Glasses were synthesized using conventional melt-quenching technique. Well-mixed starting raw materials (H\({}_{3}\)BO\({}_{3}\), Bi\({}_{5}\)OH(OH)\({}_{9}\)(NO\({}_{3}\))\({}_{4}\), Eu(NO\({}_{3}\))\({}_{3}\) and AgNO\({}_{3}\)) were melted in a porcelain crucible at 850 \({}^{\circ}\)C for 15 min. Afterward, the melts were poured onto a steel hot plate (\(\sim\)250 \({}^{\circ}\)C) and pressed by another plate immediately; they were then cooled down to room temperature. The as-prepared glasses were transparent, with a slightly yellow tint (Figure 1). To investigate the formation of Ag nanoparticles in the glassy matrix, samples were annealed at 480 \({}^{\circ}\)C for 5 h in an air atmosphere. The interval was selected based on differential thermal analysis (DTA) studies, which were performed as follows. Netzsch Simultaneous Thermal Analyzer STA 449 F1 Jupiter(R) (Netzsch, Selb, Germany) equipment was utilized for the analysis, with samples placed in a covered alumina \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **B\({}_{2}\)O\({}_{3}\)** & **Bi\({}_{2}\)O\({}_{3}\)** & **Ag** & **Eu\({}_{2}\)O\({}_{3}\)** \\ \hline BBO(50:50) & 50 & 50 & - & - \\ BBO(60:40) & 60 & 40 & - & - \\ BBO(70:30) & 70 & 30 & - & - \\ BBO(50:50) + Ag & 49.5 & 49.5 & 1 & - \\ BBO(60:40) + Ag & 59.5 & 39.5 & 1 & - \\ BBO(70:30) + Ag & 69.5 & 29.5 & 1 & - \\ BBO(50:50) + Ag + Eu & 49.25 & 49.25 & 1 & 0.5 \\ BBO(60:40) + Ag + Eu & 59.25 & 59.25 & 1 & 0.5 \\ BBO(60:40) + Ag + Eu & 69.25 & 29.25 & 1 & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Batch compositions (mol%) of the studied glasses. Figure 1: Photos of as-prepared glasses: (**a**) BBO(50:50) + Ag + Eu; (**b**) BBO(60:40) + Ag + Eu; (**c**) BBO(70:30) + Ag + Eu. crucible (sample mass \(\sim\)50 mg). The measurements were conducted in a synthetic air atmosphere at a controlled heating rate of 10 K/min. Calibration was performed to account for buoyancy effects, ensuring accurate thermal analysis for each sample within the temperature range of 45 \({}^{\circ}\)C-600 \({}^{\circ}\)C. Based on the collected data, the key thermal parameters, including glass transition temperature (Tg) and temperature at the beginning of the crystallization process (Tx) (the onset of the exothermic peak), were determined. To obtain Ag nanoparticles, samples were annealed at three different temperatures: 450 \({}^{\circ}\)C, 480 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, in the \(\Delta\)T = Tx \(-\)Tg range. Among these, samples annealed at 480 \({}^{\circ}\)C for 5 h were selected for further luminescence analysis. The most noticeable change in color was observed in the BBO(50:50) + Ag sample (a photo of which is included in the figure showing the UV-Vis results). Samples annealed at 450 \({}^{\circ}\)C showed no change in color or transparency compared to unannealed samples. In contrast, the temperature of 500 \({}^{\circ}\)C turned out to be too high, as samples lost their transparency at this temperature. The amorphous nature of the glasses was confirmed through X-ray diffraction (XRD) studies. The XRD measurements were conducted on powdered samples using a Philips X'PERT PLUS diffractometer (Philips, Amsterdam, The Netherland) with Cu-K\(\alpha\) radiation at room temperature. To identify the structural units present in the samples, Fourier transform infrared spectroscopy (FTIR) was performed. The measurements were carried out using a Perkin-Elmer Frontier MIR/FIR spectrometer equipped with a TCS detector (Perkin-Elmer, Waltham, MA, USA).