Chromium-doped forsterite (Cr:Mg2SiO4) 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:Mg2SiO4 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 Cr4+ to Cr3+ ratio in the FZ-grown Cr:Mg2SiO4 single crystal was higher than that in a Czochralski-grown crystal.
