We demonstrate a high-pressure, high-temperature sintering technique to form nitrogen-vacancy-nitrogen centres in nanodiamonds. Polycrystalline diamond nanoparticle precursors, with mean size of 25 nm, are produced by the shock wave from an explosion. These nanoparticles are sintered in the presence of ethanol, at a pressure of 7 GPa and temperature of 1300 °C, to produce substantially larger (3–4 times) diamond crystallites. The recorded spectral properties demonstrate the improved crystalline quality. The types of defects present are also observed to change; the characteristic spectral features of nitrogen-vacancy and silicon-vacancy centres present for the precursor material disappear. Two new characteristic features appear: (1) paramagnetic substitutional nitrogen (P1 centres with spin ½) with an electron paramagnetic resonance characteristic triplet hyperfine structure due to the I = 1 magnetic moment of the nitrogen nuclear spin and (2) the green spectral photoluminescence signature of the nitrogen-vacancy-nitrogen centres. This production method is a strong alternative to conventional high-energy particle beam irradiation. It can be used to easily produce purely green fluorescing nanodiamonds with advantageous properties for optical biolabelling applications.

我们展示了一种高压高温烧结技术，可在纳米金刚石中形成氮空位氮中心。爆炸的冲击波产生平均粒径为25 nm的多晶金刚石纳米颗粒前体。这些纳米颗粒在乙醇存在下，在7 GPa的压力和1300°C的温度下进行烧结，以生产出更大的（3-4倍）金刚石微晶。记录的光谱性质证明了改善的晶体质量。还观察到存在的缺陷类型会发生变化；前体材料存在的氮空位和硅空位中心的特征光谱特征消失了。出现两个新的特征：I  = 1个氮核自旋的磁矩，（2）氮空位-氮中心的绿色光谱光致发光特征。该生产方法是常规高能粒子束辐照的有力替代方法。它可用于轻松生产具有绿色荧光特性的纯绿色荧光纳米金刚石，可用于光学生物标记应用。