The resistance of a semiconductor nanoparticle provided with a surface treatment, such as an OH coating or ammonia treatment, against external factors is improved. A semiconductor nanoparticle provided with a surface treatment such as an OH coating or ammonia treatment and having high-emission properties is coated with an organic material, such as hexylamine, dodecylamine, trioctylmethylammonium, tridodecilmethylammonium, and similar organic material, by migrating the semiconductor nanoparticle from an aqueous phase to an organic solvent, such as hexane or toluene, thereby providing it with durability against external factors.