High-temperature annealing is a promising but still mainly unexplored method for enhancing spin properties of negatively charged nitrogen-vacancy (NV) centers in diamond particles. After high-energy irradiation, the formation of NV centers in diamond particles is typically accomplished via annealing at temperatures in the range of 800-900 °C for 1-2 h to promote vacancy diffusion. Here, we investigate the effects of conventional annealing (900 °C for 2 h) against annealing at a much higher temperature of 1600 °C for the same annealing duration for particles ranging in size from 100 nm to 15 μm using electron paramagnetic resonance and optical characterization. At this high temperature, the vacancy-assisted diffusion of nitrogen can occur. Previously, the annealing of diamond particles at this temperature was performed over short time scales because of concerns of particle graphitization. Our results demonstrate that particles that survive this prolonged 1600 °C annealing show increased NV T1 and T2 electron spin relaxation times in 1 and 15 μm particles, due to the removal of fast relaxing spins. Additionally, this high-temperature annealing also boosts magnetically induced fluorescence contrast of NV centers for particle sizes ranging from 100 nm to 15 μm. At the same time, the content of NV centers is decreased fewfold and reaches a level of <0.5 ppm. The results provide guidance for future studies and the optimization of high-temperature annealing of fluorescent diamond particles for applications relying on the spin properties of NV centers in the host crystals.

中文翻译：

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长时间超高温退火后荧光微米和纳米金刚石的光学和电子自旋特性。

高温退火是一种很有前景但尚未探索的方法，用于增强金刚石颗粒中带负电的氮空位 (NV) 中心的自旋特性。高能辐照后，金刚石颗粒中 NV 中心的形成通常是通过在 800-900 °C 温度范围内退火 1-2 小时以促进空位扩散来实现的。在这里，我们使用电子顺磁共振和光学研究了对于尺寸范围从 100 nm 到 15 μm 的颗粒，传统退火（900 °C，2 小时）与在更高温度 1600 °C 下退火的影响，退火时间相同。表征。在这个高温下，可以发生氮的空位辅助扩散。之前，由于担心颗粒石墨化，金刚石颗粒在此温度下的退火是在短时间内进行的。我们的结果表明，在 1600 °C 长时间退火中幸存下来的颗粒在 1 和 15 μm 颗粒中表现出 NV T1 和 T2 电子自旋弛豫时间增加，这是由于快速弛豫自旋的消除。此外，这种高温退火还增强了 NV 中心的磁致荧光对比度（颗粒尺寸范围为 100 nm 至 15 μm）。同时，NV中心的含量也减少了几倍，达到<0.5 ppm的水平。这些结果为未来的研究和荧光金刚石颗粒高温退火的优化提供了指导，这些应用依赖于主体晶体中 NV 中心的自旋特性。