Silicon-Vacancy Nanodiamonds as High Performance Near-Infrared Emitters for Live-Cell Dual-Color Imaging and Thermometry

Nanodiamonds (NDs) with color centers are excellent emitters for various bioimaging and quantum biosensing applications. In our work, we explored new applications of NDs with silicon-vacancy centers (SiV) obtained by high-pressure high-temperature (HPHT) synthesis based on metal-catalyst-free growth. They are coated with a polypeptide biopolymer which is essential for efficient cellular uptake. The unique optical properties of NDs with SiV are their high photostability and narrow emission in the near-infrared region. Our results demonstrate for the first time that NDs with SiV allow live-cell dual-color imaging and intracellular tracking. Also, intracellular thermometry as well as challenges associated with SiV atomic defects in NDs are investigated and discussed for the first time. NDs with SiV nanoemitters provide new avenues for live-cell bioimaging, diagnostic (SiV as a nanosized thermometer), and theranostic (nanodiamonds as drug carrier) applications.

Numerical study of silicon vacancy color centers in silicon carbide by helium ion implantation and subsequent annealing

Molecular dynamics (MD) simulation is adopted to discover the underlying mechanism of silicon vacancy color center and damage evolution during helium ions implanted four-hexagonal silicon carbide (4H-SiC) and subsequent annealing. The atomic-scale mechanism of silicon vacancy color centers in the process of He ion implantation into 4H-SiC can be described more accurately by incorporating electron stopping power for He ion implantation. We present a new method for calculating the silicon vacancy color center numerically, which considers the structure around the color center and makes the statistical results more accurate than the Wigner-Seitz defect analysis method. At the same time, photoluminescence (PL) spectroscopy of silicon vacancy color center under different helium ion doses is also characterized for validating the numerical analysis. The MD simulation of the optimal annealing temperature of silicon vacancy color center is predicted by the proposed new method.

Purcell enhancement of fluorescence from silicon-vacancy color centers in Mie-resonant luminescent diamond particles

Over the past two decades, nanosized diamond particles with various luminescent defects have found numerous applications in many areas from quantum technologies to medical science. The size and shape of diamond particles can affect drastically the luminescence of embedded color centers. Here we study diamond particles of 250–450 nm in size containing silicon-vacancy (SiV) centers. Using dark-field scattering spectroscopy, we found that fundamental Mie resonances are excited in the spectral range of interest. We then measured the fluorescence saturation curves under continuous excitation to estimate the effects of the excitation and Purcell factor enhancement on the luminescent properties of the studied particles. The results show that the saturation excitation intensity differs by several times for particles of different sizes which is well explained by the numerical model that takes into account both the Parcell factor enhancement and resonant excitation.

Spectral tuning of diamond photonic crystal slabs by deposition of a thin layer with silicon vacancy centers

The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.