Abstract: Method to produce diamonds containing Nitrogen-Vacancy centres from diamonds grown by a high pressure and high temperature process and containing isolated substitutional nitrogen, comprising:—Irradiating (12) said diamonds by an electron beam such that the irradiation dose is comprised between 1017 and 1019 electrons per square centimeter;—annealing (14) the irradiated diamonds in vacuum or in a inert atmosphere at a temperature above 700° C. and for at least 1 hour; characterized in that said electron beam has an acceleration energy above 7 MeV.