CVD SINGLE CRYSTAL DIAMOND

A CVD single crystal diamond having a concentration of single substitutional nitrogen atoms, Ns 0, in their neutral charge state as measured by EPR of between 0.25 and 3 ppm, and herein the CVD single crystal diamond has a total concentration of nitrogen vacancy centres in their neutral and negative charge states (NV0 and NV-) that is between 0.1 and 0.8 times the Ns 0 concentration. The CVD single crystal diamond has at least one linear dimension no less than 3.5 mm. The single crystal diamond may have a hue angle, hab, selected from any of between -45 and 45°, between -10 and 40°, and between 10 and 40°. The CVD single crystal diamond may display SiV- luminescence, quantitated by the ratio of the total peak area of the SiV- zero-phonon lines to the peak area of the first-order diamond Raman signal in a photoluminescence measurement performed at a temperature of 77 K using an excitation wavelength of 660 nm, selected from any of less than 0.5; less than 0.1; less than 0.05; and less than 0.01.