The spectra were acquired in reflectivity mode with a Bruker V70
interferometer working under dry air sweep. The measurements
were made in the range of 30 cm-1 to 2500 cm-1 in the middle and
far infrared at near normal incidence (see Fig. 11). The instrumental
resolution was 4 cm-1 and the reference measured with a gold mirror.
We deduce a global trend to a structural change of the silicate
network after staining process up to T>660 °C (the two colored
glasses) because contributions are deviated from 1030 to 1100 and
1120 cm-1 respectively from the reference glass to silver and copper glasses in Fig. 11. Typical absorption depth of the probe beam for a
glass material is of micrometer order, consequently, this method is a
qualitative surface analysis. The reflectance spectra obtained can be
fitted by the use of a reflectivity model with a dielectric function
model ε=ε'+iε' ' based on causal Gaussian absorption profiles
(Kramers-Kroenig gaussian) that are well adapted for the analysis of
amorphous materials and more especially glass [21]. This fitting
procedure of the spectra can be made with “FOCUS” [25], a curve
fitting software especially suitable for the analysis of optical spectra.
However in our particular case where values of ε∞=n2 are almost
equal beyond 1300 cm-1, we can just discuss the absorption
thanks to the reflectance and the extraction of its imaginary part
(Fig. 12).
The region in the range of 800 to 1300 cm-1 is assigned to seven
(νi) bands associated to Qn stretching modes of SiO4 tetrahedra
interconnected between them and the region below 400 cm-1 is
assigned to Na-O and Cu-O bonds [21,26]. Except (ν6) which represents
a dynamic mode at a higher scale, (ν1), (ν5) and (ν7) are related
to intertetrahedral stretching modes of Si-O-Si bridges. (ν2) and (ν3)
modes are associated to stretching vibration of Si-NBO bonds in Q2
and Q3 species. (ν4) is the Q4 stretching vibration mode. A thorough
analysis of the imaginary part of each glass is realized to understand
the structural evolution trends.