Nanoparticles having a core/shell structure consisting of a core comprising a Group III element and a Group V element at a molar ratio of the Group III element to the Group V element in the range of 1.25 to 3.0, and a shell comprising a Group II element and a Group VI element and having a thickness of 0.2 nm to 4 nm, the nanoparticles having a photoluminescence efficiency of 10% or more and a diameter of 2.5 to 10 nm; a method of producing the water-dispersible nanoparticles and a method of producing a glass matrix having the nanoparticles dispersed therein.