Diamond material

A method of introducing NV centers into CVD diamond material, the method comprising:

• (i) irradiating single crystal diamond material that has been grown by CVD, contains single substitutional nitrogen (Ns0,) and has an absorption spectrum with a total integrated absorption in the visible range from 350 nm to 750 nm such that at least 10% of the integrated absorption is attributable to Ns0, to introduce isolated vacancies V into at least part of the CVD diamond material, the concentration of isolated vacancies in the irradiated diamond material being at least 0.05 ppm and at most 1 ppm;
• and
• (ii) annealing the irradiated diamond material to form NV centers from at least some of the single substitutional nitrogen (Ns0)defects and the introduced isolated vacancies;
• wherein after the irradiation and annealing steps (i) and (ii) the treated CVD diamond material has the following characteristics:
• [V0] GR1
• <0.3 ppm
• [V] ND1
• <0.3 ppm
• [Ns0]
• <1.5 ppm
• [V chains]
• <20 cm−1 at 250 nm
• [NV]
• ≧10−12 cm−3.