An objective is to provide a nanosized semiconductor particle having a core/shell structure in which a ratio of shell thickness/core portion particle diameter exhibits an optimal ratio in optical properties of optical elements. The particle comprising the structure in which shell portion has a thickness of not more than 1/2 of core portion particle diameter, wherein core portion has a particle diameter of less than 20 nm, and shell portion has a thickness of at least 0.2 nm; core portion has a particle diameter of 20-100 nm, and shell portion has a thickness of at least 1/100 of a core portion particle diameter; core portion possesses at least one element of B, C, N, Al, Si, P, S, Zn, Ga, Ge, As, Se, Cd, In, Sb and Te; and shell portion has a composition exhibiting a larger band gap than that of core portion.