A doped-type metal sulfide phosphor nanoparticle, whose surface is modified with a surface modifier, the surface modifier being a compound of formula [I]: HS-L-W Formula [I] wherein L is a divalent linking group; and W is COOM or NH.sub.2, in which M is a hydrogen atom, an alkali metal atom, or NX.sub.4, in which X is a hydrogen atom or an alkyl group; a dispersion containing the nanoparticle; and a method of producing the nanoparticle or the dispersion.