The present quantum crystals are produced by a method characterized in that an aqueous solution of plasmon metal complex made from a ligand and a plasmon metal selected from the group consisting of gold, silver, copper, nickel, zinc, aluminum, and platinum is prepared and brought into contact with a carrier made of a metal or a metal alloy having an electrode potential lower than an electrode potential of the plasmon metal in the aqueous solution. When the plasmon metal complex is precipitated as quantum crystals arranged on the carrier, the metal complex crystals are formed as metal quantum dots.