The role of different network modifying cations on the speciation of the Co2+ complex in silicates and implication in the investigation of historical glasses

Analysis of chromophores in stained-glass windows using Visible Hyperspectral Imaging in-situ

“…6 a). The blue color in silicate glasses could be attributed to Co 2+ -ions mainly in tetrahedral coordination, although the contributions due to 5-fold and octahedral complexes can be overlapped modifying the shape and position of the bands [41,42]. In tetrahedral coordination, the main band in the visible region is due to the 4 A2 → 4 T1 (P) transition, although two other absorption bands corresponding to 4 A2 → 4 T2 and 4 A2 → 4 T1 (F) occur in the infrared region.…”

Preliminary non-invasive study of Roman glasses from Jesolo (Venice), Italy

“…(16,18,21) In particular, the position of the central VIS sub band resulted to be affected in potash-lime-silica and soda-lime-silica glass, since it shifts from ~526 nm to ~535 nm. (18) In the investigated fragments the observed absorption features perfectly match the maxima positions reported in literature for Co 2+ in tetrahedral coordination in soda-lime-silica glasses (15,16,18,21) with the spin-allowed 4 A 2 (F)AE 4 T 1 (P) transition at~ 590 nm, the spin-forbidden (very close in energy transition) 4 A 2 (F)AE 2 T 1 (G) and 4 A 2 (F)AE 2 E(G) at ~535 nm, and the spin-forbidden transition 4 A 2 (F) AE 2 T 2 (G) at 640 nm, respectively. (25) Blue glass fragments displayed, in fact, band positions between 533 and 535 nm ( Figure 6), consistent with those reported for soda-lime-silica glass, as is expected of Roman samples.…”

“…The Co 2+ spectra in the VIS range are characterised by various absorption bands due to dd transitions: this ion is predominantly tetra-coordinated but can occur also in octahedral and cubic symmetries. (16,21) As known, (16,18,21,25) the spectrum of Co 2+ consists of three main bands located in the visible and infrared region: they are indicated as υ 1 , υ 2 and υ 3 , and are all due to ligand field dd electronic transitions. (16) The υ 3 is the only band investigable in this study since it falls in the VIS spectral region and, as well as υ 2, it splits into three sub-bands because of distortions exhibited by the tetrahedral site.…”

“…Many applications of reflectance spectroscopy to historical glasses can be found in literature, (13)(14)(15)(16)(17)(18)(19)(20)(21)(22) even though this technique is predominantly employed for painted surfaces. One of the first studies focused on the glassy blue pigment smalt; (16) this study of the Co 2+ environment was fundamental in understanding the reasons for the pigment fading.…”

“…(16) The υ 3 is the only band investigable in this study since it falls in the VIS spectral region and, as well as υ 2, it splits into three sub-bands because of distortions exhibited by the tetrahedral site. (16,21) Variation in Co 2+ band positions as a function of glass chemistry has been extensively studied in recent years, (16,20,21) revealing shifting relatable, e.g. to different fluxes introduced in the batch.…”