Optical glass-ceramics based on Fe$^{2+}$: MgAl$_2$O$_4$ nanocrystals and nucleated by TiO$_2$ and ZrO$_2$

Transparent glass-ceramics of magnesium aluminosilicate system based on Fe$^{2+}$: MgAl$_2$O$_4$ spinel nanocrystals nucleated by a mixture of TiO$_2$ and ZrO$_2$ and doped with 0.6 mol% FeO were developed. The glass was melted at 1580$^\circ$C with stirring and heat-treated in the temperature range from 800 to 1300$^\circ$C. The structure and spectroscopic properties of the glass and glass-ceramics were studied by DSC and XRD methods, Raman and absorption spectroscopy. ZrTiO$_4$ nanocrystals 6 nm in size precipitate during the nucleation heat-treatment at 800$^\circ$C. Spinel nanocrystals 9–14 nm in size are formed during heat-treatments at 850–1000$^\circ$C. Intense absorption at $\sim$2$\mu$m is observed due to Fe$^{2+}$ ions in tetrahedral positions in these crystals. Iron-doped sapphirine crystallization in transparent glass-ceramics at 1000–1050$^\circ$C results in a decrease of absorption in this spectral range. The glass-ceramics are important for the development of saturable absorbers for the spectral range of 2–3$\mu$m.