# Spectroscopic and Microscopic Characterization of Flashed Glasses from Stained Glass Windows
## 3 Results and Discussion
### Chemical Characterization
#### 3.2.3 Laser-Induced Fluorescence  
The LIF spectra collected on the flashed glasses of this study are displayed in Figure 6. All spectra consist of a broad feature in the 300-700 nm wavelength range, although each sample displays different characteristics that are associated with its chemical composition, including chromophores.  
The LIF spectra corresponding to the base glass of the different samples (black lines in Figure 6) are rather similar and can be described as the sum of emissions from different glass components. The emission in the 300-500 nm range encompasses the contribution of oxygen deficiency centers (ODC) from the glass network [42; 44; 48]. Besides, an additional shoulder with different relative intensities in each sample is noticed around 520 nm and assigned to Ca\({}^{2+}\) of the glass lattice [39; 49].  
Figure 6: _Cont._  
Figure 6: LIF spectra of base glass (lower black spectra) and colored layers (upper red spectra) from flashed glasses. ODC and (*) refer to bands due to oxygen deficiency centers and copper nanoparticles, respectively. Possible chromophores are tentatively assigned and marked by horizontal bars. (**a–k**) correspond to LIF spectra of samples Pink1, Pink2, Brown1, Brown2, Blue1, Blue2, Blue3, Black, Green1, Green2 and Green3, respectively.  
The LIF spectra of colored layers (red lines in Figure 6) display some specific features in addition to those observed in the base glass. As already indicated and revealed by FESEM-EDS, UV-Vis-IR spectroscopy, and LIBS, chromophores based on Fe, Cu, Mn, Co, Ni, and Cr account for the different colorations. The contribution of these chromophores to fluorescence emissions of the colored layers is not much evident in the LIF spectra of the samples due to the expected reabsorption of the fluorescence from these compounds with absorption bands in the near-UV and visible spectral ranges. Despite this, the weak shoulders over-imposed on the main emission band and observed at 360, 475, 500, 540, and 610 nm have been tentatively attributed to the presence of Fe\({}^{3+}\)/Fe\({}^{2+}\), Cu\({}^{2+}\), Fe\({}^{3+}\), Mn\({}^{2+}\), and Mn\({}^{3+}\), respectively [40; 45]. On the other hand, the prominent bands observed around 580 nm, specifically for the dark-colored layers from the samples Pink2 and Brown2, may be assigned to emissions from copper nanoparticles [19].  
The light coloration from samples Pink1 and Brown1 is due to the presence of Mn- and Fe-based chromophores, while the additional emissions attributed to copper nanoparticles account for the dark hue of Pink2 and Brown2 samples, in agreement with LIBS and FESEM-EDS results. Emissions attributed to different chromophores contribute to the black coloration in the Black sample, as also revealed by LIBS and FESEM-EDS. Regarding the green and blue samples, Cu, Fe, and Mn with different amounts and contributions are considered chromophores in these samples [19].  
The combination of LIF and UV-Vis-IR spectroscopy techniques has been revealed to be very effective for the determination of the chromophores responsible for the coloration of glasses, although the latter has shown high sensitivity with respect to the former, revealing the presence of a very high number of chromophores.