CVD single crystal diamond

CVD single crystal diamond having a smallest linear dimension of no less than 3.5 mm, a concentration of single substitutional nitrogen atoms in their neutral charge state (Ns0), as measured by EPR, of between 20 and 250 ppb, a hue angle, hab, between 75 and 135°. The diamond may have a total concentration of nitrogen vacancy centres in their neutral and negative charge states (NV0 and NV) less than the greater of 0.1 times the Ns0 concentration of 10pbb. The hue angle may be selected from any of between 85 and 125°, between 90 and 120° and between 95 and 115°. The diamond may display SiV- luminescence, quantified by a ratio of a total peak area of SiV- sero-phonon lines to a 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 660nm, selected from any of less than 0.5; less than 0.1; less than 0.05; and less than 0.01. The total volume of the single crystal CVD diamond material is selected from any of at least 60mm3, at least 80mm3 and at least 100mm3.