| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1251907 | Vibrational Spectroscopy | 2013 | 11 Pages |
Irradiation and heat treatment were performed on tourmalines of various colors from Antandrokomby, Madagascar. The samples were irradiated with 10 MeV electrons to fluencies of 2 ×1017 cm−2 for 1 h and were heated at 550 °C for 3 h in air. Their electronic and vibrational spectra were investigated by UV–vis, mid-infrared, and WD-XRF spectroscopy for comparison to pristine samples. Changes in the Mn3+ ions after irradiation resulted in darker pink tourmalines, which had absorption peaks at 390 and 520 nm. These samples became colorless after subsequent heat treatment. After irradiation, colorless, light blue and yellow tourmalines displayed a new absorption band at 365 nm. Alteration of the stretching absorption bands and wavenumber after irradiation could be explained by the following reactions:OH− + e− beam irradiation → O− + H°,Mn2+ + e− beam irradiation → Mn3+ + e− andFe2+ + e− beam irradiation → Fe3+ + e−.Stretching vibration of the BO3 structure occurred at 1330 cm−1, while the SiO vibration absorption bands were assigned to around 1100 cm−1. Colorless, green, and yellow tourmalines showed high-intensity peaks around 3608 and 3505 cm−1 after irradiation. Pink and dark green tourmalines showed low-intensity peaks at 3605 and 3585 cm−1, respectively. The combination modes of stretching and bending in the range of 4600–4300 cm−1 were split after irradiation and heat treatment, and different color changes occurred after irradiation.
► The light yellow tourmaline containing Mn changed to vivid red after irradiation. ► Pink tourmalines with a high Mn content changed to a darker pink after irradiation. ► After irradiation, alteration of the absorption bands could be described as follows; OH− + e− beam irradiation → O− + Ho, Mn2+ + e− beam irradiation → Mn3+ + e− and Fe2+ + e− beam irradiation → Fe3+ + e−. ► The spectra of the changed tourmalines reverted back to the spectra of the pristine samples after heat treatment.
