Influence of Cr₂O₃ Concentration on the Green Color of Flux Synthesized Emeralds Using the CIE1976 Color System

Abstract The color of emeralds is predominantly influenced by the concentration of Cr 3+ . However, the evaluation of the trend of green color depth of emeralds, based on the practical single crystal synthesis with several instrumental analysis is not investigated in previous researches. Specifically, if the Cr 2 O 3 content is controlled to be in the range of 0.2–0.4 wt%, then emeralds can be synthesized with the most esthetically pleasing color. Therefore, the effect of Cr 2 O 3 concentration within the aforementioned range on the color of emeralds is studied using powder X‐ray diffractometry, digital microscopy, electron probe microanalysis, and micro‐spectrophotometry to understand how to achieve the most esthetically pleasing color. As a result, detailed behaviors relating to the absorbances, L * , a * , and b * values, and the relationship between the emerald crystal color changes and increases in Cr 2 O 3 concentration are elucidated. Notably, the absorbance, L * and a * values change significantly when the Cr 2 O 3 concentration is low (0.00–0.236 wt%). However, the changes in these values are moderate when the Cr 2 O 3 concentration is higher (0.236–0.504 wt%).