Influence of degree of air oxidation and functionality on ensemble emission from nitrogen vacancy centers in nano-diamonds

Abstract

Oxygen functionalities in Nano-diamonds (NDs) are accepted as emission and photo-stability enhancer of nitrogen vacancy (NV) centers. In this direction, we have investigated the effect of functional groups and oxygen content on emission and stability of NV centers at ensemble level. Optimized air oxidation conditions (600 °C, 2 h) and hydrogen plasma treatment (500 °C, 20 min) are used to vary functionality and oxygen content. The emission from NV centers in plasma treated NDs (–OH group) is ~ 5 times higher as compared to oxidized sample (-OH, CO and COOO). The probability of finding emitting NV center in any crystallite is ~52% for plasma treated NDs; much higher than oxidized sample (~7%). Confocal microscopy revealed continuous emission blinking from air oxidized sample and stable emission (~ 8 min) for plasma treated NDs. We propose that laser excitation causes detachment of oxygen from –OH, CO and COOO groups and formation of electron trapping states at surface in oxidized sample which leads to NV emission blinking. Whereas, the –OH group detached from plasma treated NDs has electron withdrawing nature. Hence, emission as well as photo stability of NV centers is increased upon reducing degree of oxidation and changing functionality in NDs.