Semiconductor nanoparticles, method of producing semiconductor nanoparticles, and light-emitting device

A core-shell semiconductor nanoparticle comprising:

• a core;
• and
• a shell covering a surface of the core, the shell being in heterojunction with the core, wherein
• the core is made of a semiconductor that contains Ag, In, and S, wherein a ratio of a number of atoms of Ag to a total number of atoms of Ag and In is 0.320 or more and 0.385 or less, and a ratio of a number of atoms of S to the total number of atoms of Ag and In is 1.20 or more and 1.45 or less,
• the shell is a semiconductor that consists essentially of a Group 13 element and a Group 16 element, and
• in a photoluminescence spectrum obtained when the core-shell semiconductor nanoparticle is irradiated with light having a wavelength in a range of 350 nm to 500 nm, a photoluminescence peak having a peak wavelength in a range of 550 nm to 650 nm and a full width at half maximum of 80 nm or less is observed.