NOVELTY - A light-emissive nitride nanoparticles which has photoluminescence quantum yield (PLQY) of at least 10% and has emission spectrum having a full width at half maximum intensity (FWHM) of less than 100 nm.    USE - In phosphor converted light emitting diodes (LEDs), emissive displays, solar cells, and bio-imaging; as a light source in display devices such a television or portable devices such as tablets.    ADVANTAGE - The light-emissive nitride nanoparticles has photoluminescence quantum yield (PLQY) of at least 10 (preferably greater than 20, more preferably greater than 30, especially is greater than 40, particularly greater than 50)% and emission spectrum having a full width at half maximum intensity (FWHM) of less than 100 (preferably less than 90, more preferably less than 80, especially less than 70) nm. The nanoparticles have a more consistent size, so that variations in size between nanoparticles of the population are less than for prior art nanoparticles. As a result, the emission spectrum of a population of nanoparticles is narrower than the emission spectrum of a prior art nanoparticles. The nanoparticles is prepared by a method that provides good uniformity of nanoparticle size, that is less variation in size between nanoparticles; and obtains nanoparticles that is highly emissive but that has a narrower emission spectrum than prior nanoparticles. The nanoparticles when used as light sources have an improved color gamut, and the higher PLQY of nanoparticles that a device in which nanoparticles are used as light sources have a greater efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for producing (M1) light-emissive nitride nanoparticles involves: heating a reaction mixture comprising nanoparticle precursors in a solvent, where the nanoparticle precursors includes at least one metal-containing precursor and at least one first nitrogen-containing precursor, and maintaining the reaction mixture at a temperature to seed nanoparticle growth; and adding at least one second nitrogen-containing precursor to the reaction mixture thus to promote nanoparticle growth.