Provided are core-shell semiconductor nanoparticles, each including a core and a shell disposed on a surface of the core, and emitting light when irradiated with light. The core contains a semiconductor containing M1, M2, and Z, M1 containing at least one selected from the group consisting of Ag, Cu, and Au, M2 containing at least one selected from the group consisting of Al, Ga, In, and Tl, and Z containing at least one selected from the group consisting of S, Se, and Te. The shell contains a semiconductor containing a Group 13 element and a Group 16 element, and having a greater band-gap energy than the core. The shell has a compound containing a Group 15 element disposed on a surface of the shell, and the Group 15 element containing at least P with a negative oxidation number.