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A composite particle including a core member including a rare earth ion which shows an upconversion effect and a retaining material which retains the rare earth ion, and a semiconductor member covering a part or all of the surface of the core member, wherein the retaining material includes a semiconductor material having a band gap greater than energy difference necessary for a second step excitation in the rare earth ion to occur, or an insulating material, and the semiconductor member includes a semiconductor material having a band gap smaller than the energy difference between a first excited state and a ground state of the rare earth ion.