Effect of the electrical furnace cooling rate on the formation of a pale-green surface layer during the flux synthesis of emerald

Abstract The flux method is a process that is commonly employed for growing a single crystal or crystals of metals or compounds. In general, the flux method can be subdivided into three different approaches, namely the slow cooling, temperature-gradient, and evaporation methods. In this research, the effect of the furnace cooling rate during the growth of emerald crystals is examined via the evaporation method. More specifically, emerald crystal growth and the formation of a pale green surface layer are investigated during quick cooling (natural cooling) and slow cooling from 1,100 °C. In addition, the relationships between the Cr2O3 dopant content during flux synthesis, the Cr2O3 content in the grown emerald crystals, and the depth of the green color is re-evaluated. The obtained results suggest that emerald crystals are grown using both slow cooling and evaporation approaches. Furthermore, a detailed re-evaluation of emerald crystal color changes based on increases in the crystal Cr2O3 content is achieved. Accordingly, the behaviors of the L*, a*, and b* values in response to changes in Cr2O3 content are accurately elucidated in the grown emerald crystals.