Photoluminescence studies of NV and SiV centers in diamond nanostructures and nanoparticles

Diamond poses a unique combination of physical and chemical properties, which make this material promising for bio- and optoelectronics, and quantum computing. It is chemically stable, compatible with biological tissue, and its surface can be modified by a wide range of functional groups. The outstanding properties inherent to diamond are multiplied by optically active centers. One of the fabrication ways is based on the plasmo-chemical etching of Si substrates or Si-containing parts of the experimental apparatus occurring during the chemical vapor deposition (CVD), the negatively-charged silicon-vacancy color centers (SiV) are naturally incorporated into diamonds. The exceptionality of the SiV centers resides in the bright and spectrally narrow photoluminescence (PL) at room temperature, with the short decay time about 1 ns and their high photostability. Next, SiV centers in diamond are often cited in connection with applications as single-photon sources, or biocompatible fluorescent markers for bio- imaging, where they could surpass recently used nitrogen-vacancy centers (NV). Nowadays, mentioned PL properties of SiV centers became interesting for optical sensing. It was shown that the PL intensity of SiV centers is sensitive to the surface termination of diamond thin films.

This finding implies that by choice of functional groups is possible to control PL activity of the centers, i.e., to switch On or Off PL in the near presence of biomolecules. In addition, PL generally reflects the coupling of the center with the local environment. Only a small change in the system bring about noticeable changes in PL response, which would enable to detect the evolution of the studied system. The NV center in diamond is also being intensively studied for sensing applications. Its spin-dependent fluorescence signal can indeed be used to detect tiny magnetic fields and to measure temperature at the nanoscale.

Because the NV center is also naturally occurring in diamond, we believe that a combined study of SiV and NV in diamond nanostructures would be of interest for developing novel sensing approaches. Moreover, the controlled fabrication of SiV and NV centers in nanoscale diamond is still a challenging issue. We hypothesize that using new plasma chemistries (CO2 based or doping from liquid source) provides new challenges for the growth of high-quality diamond films either of intrinsic or doped character. Here, the centers can be fabricated by both approaches, i.e., bottom up (BU) and top-down (TD), respectively. Furthermore, the centers can be activated by proton or electron irradiation followed by thermal annealing. In addition, the PL parameters can be influenced by temperature and local electromagnetic fields, such that a judicious combination of NV and SiV centers can be exploited to sense at the same time multiple parameters.

Focus Areas of the project

• The project focuses on the complementary study of the German partners of the Laboratory of Nano-Optics, University of Siegen, who will provide advanced optical methods, such as micro-Raman and PL spectroscopy, fluorescence lifetime imaging microscopy (FLIM) and atomic force microscopy (AFM) and optically detected magnetic resonance (ODMR) combined with polarimetry.

• Thin diamond films and diamond nanocrystals with integrated luminescence color centers will be fabricated and processed by the Czech partners at the Institute of Physics of CAS, a group with to profound expertise in diamond fabrication, structuring and optical properties of color centers in diamond.

• Based on obtained results, optimization of systems will be proposed, which could lead in the future to applications in nanoscale multiparametric sensing.

This project is financed by Deutscher Akademischer Austauschdienst (DAAD) within „Programmes for Project-Related Personal Exchange (PPP) from 2024 with Czech Republic“.

Cooperation Partner: Kateřina Aubrechtová Dragounová, Institute of Physics, Czech Academy of Sciences (CAS)