A method for preparing a quantum dot includes supplying a first mixture including a first precursor material including a silver precursor, an indium precursor, a first gallium precursor, and a first solvent including oleylamine, trioctylphosphine oxide, and trioctylamine, adding a first sulfur precursor to the first mixture to form cores including silver, indium, gallium, and sulfur, reacting the cores with a second precursor material including a second sulfur precursor and a second gallium precursor to form a first shell around each of the cores, wherein the cores including the first shells comprise first particles, and adding a first element precursor and a second element precursor to a second mixture, the second mixture including the first particles and a second solvent, to form a second shell around each of the first shells.