Taras Plakhotnik

Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds

Nitrogen-vacancy colour centres in diamond can undergo strong, spin-sensitive optical transitions under ambient conditions, which makes them attractive for applications in quantum optics, nanoscale magnetometry and biolabelling. Although nitrogen-vacancy centres have been observed in aggregated detonation nanodiamonds and milled nanodiamonds, they have not been observed in very small isolated nanodiamonds. Here, we report the first direct observation of nitrogen-vacancy centres in discrete 5-nm nanodiamonds at room temperature, including evidence for intermittency in the luminescence (blinking) from the nanodiamonds. We also show that it is possible to control this blinking by modifying the surface of the nanodiamonds.

Five-nanometer diamond with luminescent nitrogen-vacancy defect centers

A study was conducted to investigate the properties of weakly bound clusters of single-digit nanodiamonds (SND) using spectrally and temporally resolved luminescence detection, electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (SEM). Nitrogen-vacancy (NV) centers were created in diamonds by high-energy proton irradiation followed by thermal annealing. Samples containing equal weights of 55-nm HTHP diamonds and SNDs were uniformly distributed on quartz substrates for luminescence measurements. It was observed that the SNDs exhibited significant luminescence in the red spectral region before irradiation. The emission was blue-shifted and the absence of the zero-phonon lines at 637 and 575 nm indicated that the luminescence did not originate from NV centers as compared with the NV spectrum.

Fluorescence microscopy of single molecules

Abstract Using fluorescence excitation spectroscopy single pentacence molecules were studied under a microscope at a temperature of 1.8 K. The microscope has a resolution of 3 μm and allows the location of a single emitting molecule with an accuracy of 0.5 μm, in a total viewing field of 235 μm×175 μm. 133 images have been recorded by increasing the excitation frequency of the light at 592.344 nm in steps of 2 MHz. Each single molecule has a Lorentzian absorption profile with a width of about 14 MHz and can be observed in 10 consecutive images. The “position” of the single molecule is characterized by the x - and y -coordinates in the spatial domain and by its absorption frequency in the spectral domain.

Single molecule spectroscopy: maximum emission rate and saturation intensity

Abstract We consider the collection efficiency for photons emitted by a single molecule in a solid excited by monochromatic light at low temperature, which depends upon the dipole radiation pattern, the orientation of the emission dipole, total internal reflection, and the numerical aperture of the collecting optics. By using the complete expression for the collection efficiency and varying the collection angle, we have determined the orientation of the dipole of a single terrylene molecule in hexadecane to be almost perpendicular to the substrate. By using saturation data we find that the angle between the optical axis of the collection paraboloid and the emission dipole moment is 16±6°. We estimate that the true saturation intensity of terrylene (for dipole moment parallel to the electric field of the light) is about (80±30) mW/cm 2 and that the ratio of the intersystem crossing rate to the total decay rate of the triplet state is about 3.3±1.2.

Nonlinear Spectroscopy on a Single Quantum System: Two-Photon Absorption of a Single Molecule

Two-photon fluorescence excitation spectra of single diphenyloctatetraene molecules trapped in an n-tetradecane matrix were measured at cryogenic temperatures. The purely electronic zero-phonon line (transition at 444 nanometers) of these single molecules with a width of about 60 megahertz was excited by a continuous-wave, single-mode laser at 888 nanometers. Even though the two-photon absorption cross section is extremely small, a high photon count rate and low background allowed nonlinear spectroscopy to be extended to the single-molecule level. This experiment also suggests the possibility of two-photon single-molecule scanning microscopy.

Single molecule spectroscopy: fluorescence excitation spectra with polarized light

The orientations of the transition dipole moments of single pentacene molecules located in the O-1 and O-2 site of p-terphenyl were investigated. Two distinct orientations were found for most of the molecules. The results are discussed with respect to the crystallographic structure of the p-terphenyl host crystal.

All-Optical Thermometry and Thermal Properties of the Optically Detected Spin Resonances of the NV– Center in Nanodiamond

The negatively charged nitrogen-vacancy (NV(-)) center in diamond is at the frontier of quantum nanometrology and biosensing. Recent attention has focused on the application of high-sensitivity thermometry using the spin resonances of NV(-) centers in nanodiamond to subcellular biological and biomedical research. Here, we report a comprehensive investigation of the thermal properties of the centers spin resonances and demonstrate an alternate all-optical NV(-) thermometry technique that exploits the temperature dependence of the centers optical Debye-Waller factor.

Imaging and sizing of diamond nanoparticles

Typical disturbances of biological environment such as background scatter and refractive index variations have little effect on the size-dependent scattering property of highly refractive nanocrystals, which are potentially attractive optical labels. We report on what is to our knowledge the first investigation of these scattering optical labels, and their sizing, in particular, by imaging at subvideo frame rates and analyzing samples of diamond nanocrystals deposited on a glass substrate in air and in a matrix of weakly scattering polymer. The brightness of a diffraction-limited spot appears to serve as a reliable measure of the particle size in the Rayleigh scattering limit.

Dependence of the Sensitivity of Intracavity Laser Spectroscopy On Generation Parameters

Abstract The dependence of the sensitivity of intra-cavity laser spectroscopy (ILS) at the transition stage of generation on the pumping power and spectral width has been investigated experimentally. The time interval of linear growth of the sensitivity is shown to be limited and determined by the excess of the pumping power over the threshold. The combination of physical parameters of the system which determines the value of the effect is found. Possible mechanisms of the phenomenon are discussed. Insufficiency of the generally accepted description of a multimode laser in ILS within the frames of rate equations and the necessity of the inclusion of parametric processes are pointed out.

Luminescence of nitrogen-vacancy centers in nanodiamonds at temperatures between 300 and 700 K: perspectives on nanothermometry

It is shown that the intensity of photoluminescence of nitrogen-vacancy (NV) centers in nanodiamond decreases 4-fold (with a wide spread among nanocrystals) when the surrounding temperature rises from 300 to 670 K. The effect is accompanied by a 2.7-fold decrease in the luminescence lifetime but negligible changes in the shape of the emission spectra. The heating-cooling circle is reversible. The effect is suggested to be practically useful for thermometry with nanometre spatial resolution but also stimulates deeper insight into the photophysics and photochemistry of NV-centers.