Purification method dependent fluorescence from nitrogen-vacancy (NV) centers of nano-diamonds

Abstract

Fluorescent nanodiamonds (FNDs) with high photo stability at a subwavelength scale are highly desirable for nano-photonics and bio-imaging applications. Nanodiamonds (NDs) with embedded fluorescent color centers made by ion-implantation need to be purified to remove the sp² layer on their surfaces which significantly degrades the optical properties. In this work, we discuss the structural and photo physical properties of NDs containing nitrogen-vacancy (NV) centers prepared by two different purification methods; chemical etching (H₂SO₄:HNO₃) and air oxidation (450 °C). Chemically etched NDs show better uniformity in their shape, de-aggregation and higher dispersibility in water as compared to air oxidized ones. On the other hand it is observed that air oxidation is more effective in removing the sp² layer and allows a higher fluorescence photon flux. Therefore, we suggest that air oxidation is more appropriate for bright fluorescent sources, and chemical etching is more appropriate for fluorescent markers in bio-imaging applications with high uniformity in shape and good dispersibility.