Growth of Cr4+-rich, chromium-doped forsterite single crystals by the floating zone method

Abstract Chromium-doped forsterite (Cr:Mg 2 SiO 4 ) single crystals were successfully grown by a floating zone method in an oxygen stream. Bubble formation in the melt zone was effectively avoided by using a premelted feed rod, so that a steady growth was possible to obtain single crystals with a uniform diameter. An after-heater placed just below the melt zone rendered the liquid-solid interface convex toward the melt to prevent the crystals from cracking. The chromium concentration of the grown crystal was almost uniform along the growth direction. Cr:Mg 2 SiO 4 crystals cut perpendicularly to each crystallographic axis show typical pleochroism, i.e., blue, purple and green along the a -, b - and c -axis, respectively. The emission spectra proved that the Cr 4+ to Cr 3+ ratio in the FZ-grown Cr:Mg 2 SiO 4 single crystal was higher than that in a Czochralski-grown crystal.