A refractive index variable element has a structure including a solid matrix, and one or more types of quantum dots dispersed in the solid matrix and having discrete occupied and unoccupied electron energy levels. The quantum dots perform a function of generating a pair of positive and negative charges upon irradiation with light, a function of trapping a positive charge, and a function of trapping a negative charge. The quantum dots performing the function of trapping a negative charge are selected from the group consisting of a combination of a negatively charged accepter and a positively charged atom, where the outermost electron shell of the positively charged atom is fully filled with electrons so that an additional electron occupies an upper different shell orbital when receives an electron, a metal chelate complex, and metallocene and derivatives thereof.