Optical properties and crystallization behaviour of some MnO and/or Fe2O3-containing silicate glasses and glass-ceramics

Abstract Glass and glass-ceramics with the compositions 1Fe 2 O 3 -99SiO 2 (1Fe), 2Fe 2 O 3 -98SiO 2 (2Fe), 1MnO-99SiO 2 (1Mn), 2MnO-98SiO 2 (2Mn), 1MnO-1Fe 2 O 3 -98SiO 2 (2MnFe), 2MnO-2Fe 2 O 3 -96SiO 2 (4MnFe) (mol%) were prepared using the sol-gel method. The gel samples were heat treated between 120 and 1000 °C. Thermogravimetric and differential thermal analysis (TG-DTA), ultraviolet, visible and near infrared spectrophotometry (UV–Vis-NIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (SEM-EDS) were used to study the structural changes that occur during the gel to glass and glass-ceramic conversions. Many of the prepared glass and glass-ceramics present brown or black colorations. These dark colorations are due to the presence in the samples of maghemite-C, magnetite, hematite, Mn 3 O 4 (bixbyite) and Mn 2 + (Mn 3 + ) 14 SiO 24 (braunite) or simultaneously more than one of these crystalline phases. These nanoparticles give to the samples very interesting magnetic and optical properties of great importance in several medical fields. Furthermore, the study contributed to understanding the formation mechanism of some MnO and/or Fe 2 O 3 -containing silicate glasses and glass-ceramics prepared by the sol-gel method.