## 3 Results and Discussion
### Luminescent Properties of Silver Molecular Clusters Formed in Ce- and Sb-Doped Glasses
For example, a PLQY value as high as 65%, which is among the highest reported values for glasses doped with SMCs [36], was achieved in PTR-Sb2 glass containing only 0.002 mol.% of Sb2O3. An increase in Sb2O3 content to 0.01 mol.% led to almost a twofold decrease in photoluminescence quantum yield. Heat treatment at temperatures below the glass transition temperature was found to result in bright photoluminescence due to the growth of SMCs. PLQY magnitude increases with heat treatment temperature up to 450 \({}^{\circ}\)C. Heat treatment at 500 \({}^{\circ}\)C, i.e., above the T8 value of the studied antimony-doped glass samples, led to the appearance of an absorption band around 420 nm corresponding to the localized surface plasmon resonance of SNPs (Figure 15a). The growth of SNPs inevitably caused luminescence quenching due to the absorption of SMC emission and the decrease in concentration of emission centers due to the transformation of SMCs into SNPs (Figure 15b). Figure 14: Absorbance (**a**) and emission (**b**) spectra of undoped PTR-M and antimony-doped PTR glass samples ion-exchanged for 15 min and heat-treated at 450 \({}^{\circ}\)C for 15 h. The excitation wavelength was 350 nm. Figure 15: Absorbance (**a**) and emission spectra (**b**) of PTR-Sb10 glass samples as-synthesized, ion-exchanged, and heat-treated after the IE process at different time for 15 h. The excitation wavelength was 350 nm. IE parameters, including silver content in the salt melt, temperature, and time, can also be used to tune the optical properties of silver nanostructures in Na+-Ag+ ion-exchanged glasses. The IE time and temperature influence the diffusion rate and, as a result, the thickness of the silver-enriched glass layer. Thus, these parameters change the properties of the obtained silver nanostructures in a similar way. It was found that varying IE time allows tuning the location of SMC emission in a wide spectral range. This opens up prospects for developing highly efficient, thermostable, solid-state LEDs based on PTR glasses with SMCs. The effect of the IE time on the absorbance and emission of SMCs is demonstrated in Figures 16 and 17. Emission color varied from cool white to warm and orange upon increasing the IE time (Figure 16c). It should be noted that the PLQY of the samples decreased from 60% to 15% with the extension of IE duration [37]. This effect is related to the increase in absorbance of the remaining silver ions at the excitation wavelength with an increase in the IE time (a longer IE process leads to a higher amount of silver remaining in ionic form in the PTR glass due to the constant concentration of reducing agent). However, we believe that PLQY values can be substantially increased by using a salt melt with low silver content. The silver concentration in subsurface layers of the Na+-Ag+ ion-exchanged glass is known to nonlinearly depend on the silver content in the salt melt for most glasses. Typically, the surface concentration of silver grows exponentially with AgNO3 content below 5 mol.% and saturates at greater values [57]. IE with a low silver content may allow decreasing the absorption of silver ions that remain in the PTR glass after the heat treatment. The presented results show that the photoluminescence properties of SMCs in the PTR glass matrix can be tuned in a wide range by controlling the concentration of reducing agents, as well as the parameters of the Na+-Ag+ IE and subsequent heat treatment processes. The wide emission spectrum of SMCs in the ion-exchanged PTR glass matrix and the high PLQY magnitude pave the way for applications of such glasses in lighting as phosphors for white LEDs and in photovoltaics as spectral converters. Figure 16: Absorbance (**a**) and emission (**b**) spectra of PTR-Sb2 glass samples ion-exchanged for different time and heat-treated at 450 \({}^{\circ}\)C for 15 h. The excitation wavelength was 350 nm. (**c**) Photos of the same samples in daylight (**top row**) and UV light (**bottom row**).