A complex crystal is composed of anion of triiodine and cation of a fused compound consisting essentially of at least one nitrogen atom and at least 3 aromatic fused rings. Since the complex crystal has such a stable structure, it shows excellent heat resistance and excellent moisture resisting property. Furthermore, the complex crystal has light-polarizing performance because of an arrangement of the molecular chain of iodine. Moreover, the complex crystal exhibits excellent polarization because of an interaction between the fused compound and iodine. Therefore, the complex crystal is suitable for use as light-adjusting particles of a light valve or a light-adjusting glass.