NV-centers in Nanodiamonds: How good they are

This paper presents a method for determination of the size distribution for diamond nanocrystals containing luminescent nitrogen-vacancy (NV) centers using the luminescence intensity only. We also revise the basic photo physical properties of NV centers and conclude that the luminescence quantum yield of such centers is significantly smaller than the frequently stated 100\%. The yield can be as low as 5\% for centers embedded in nanocrystals and depends on their shape and the refractive index of the surrounding medium. The paper also addresses the value of the absorption cross-section of NV centers

The electron-phonon processes of the nitrogen-vacancy center in diamond

Applications of negatively charged nitrogen-vacancy center in diamond exploit the center's unique optical and spin properties, which at ambient temperature, are predominately governed by electron-phonon interactions. Here, we investigate these interactions at ambient and elevated temperatures by observing the motional narrowing of the center's excited state spin resonances. We determine that the center's Jahn-Teller dynamics are much slower than currently believed and identify the vital role of symmetric phonon modes. Our results have pronounced implications for center's diverse applications (including quantum technology) and for understanding its fundamental properties.Comment: 5 pages, 4 figure

Relation between raman backscattering from droplets and bulk water: Effect of refractive index dispersion

A theoretical framework is presented that permits investigations of the relation between inelastic backscattering from microparticles and bulk samples of Raman-active materials. It is based on the Lorentz reciprocity theorem and no fundamental restrictions concerning the microparticle shape apply. The approach provides a simple and intuitive explanation for the enhancement of the differential backscattering cross-section in particles in comparison to bulk. The enhancement factor for scattering of water droplets in the diameter range from 0 to 60 mu m (vitally important for the a priori measurement of liquid water content of warm clouds with spectroscopic Raman lidars) is about a factor of 1.2-1.6 larger (depending on the size of the sphere) than an earlier study has shown. The numerical calculations are extended to 1000 mu m and demonstrate that dispersion of the refractive index of water becomes an important factor for spheres larger than 100 mu m. The physics of the oscillatory phenomena predicted by the simulations is explained. (C) 2018 Elsevier Ltd. All rights reserved

Accurate absolute measurements of the Raman backscattering differential cross-section of water and ice and its dependence on the temperature and excitation wavelength

Measurements of Raman backscattering spectra between -15 C-omicron and 22 C-omicron in liquid water (including its supercooled state) and in polycrystalline ice (-35 C-omicron to 0 C-omicron) at two excitation wavelengths (407 and 532 nm) are presented. It is found that the spectrum-integrated backscattering cross-section of the 3400 cm(-1) band is about 1.2 times larger for ice in comparison to liquid water. The excitation-wavelength dependence of the cross-section in ice is very close to that in water. A discontinuous change of the spectrum is observed upon phase transition at 0 C-omicron. The results are applicable to preliminary calibration of lidar systems designed for water content surveys in the atmosphere. (C) 2017 Elsevier Ltd. All rights reserved

Fluorescence profile of an NV centre in a nanodiamond

Nanodiamonds containing luminescent point defects are widely explored for applications in quantum bio-sensing such as nanoscale magnetometry, thermometry, and electrometry. A key challenge in the development of such applications is a large variation in fluorescence properties observed between particles, even when obtained from the same batch or nominally identical fabrication processes. By theoretically modelling the emission of nitrogen-vacancy colour centres in spherical nanoparticles, we are able to show that the fluorescence spectrum varies with the exact position of the emitter within the nanoparticle, with noticeable effects seen when the diamond radius, $a$, is larger than around 110 nm, and significantly modified fluorescence profiles found for larger particles when $a=200$ nm and $a=300$ nm, while negligible effects below $a=100$ nm. These results show that the reproducible geometry of point defect position within narrowly sized batch of diamond crystals is necessary for controlling the emission properties. Our results are useful for understanding the extent to which nanodiamonds can be optimised for bio-sensing applications

Charge hopping revealed by jitter correlations in the photoluminescence spectra of single CdSe nanocrystals

Spectral fluctuations observed in single CdSe/ZnS nanocrystals at 5 K are found to be entirely the result of discrete charge hops in the local environment of the nanocrystal, which occur at a rate comparable to the acquisition time of a single spectrum. We show that intervals between discrete spectral hops introduce a correlation between the successive measurements of the emission wavelength of single CdSe nanocrystals. This correlation can be recovered even in the presence of noise, but is shown to be sensitive to the experimental acquisition time, in good agreement with theory. However, we only find correlations for the smaller of the two nanocrystal sizes studied and discuss this in terms of size-dependent time scales correlated with the amount of excess energy dissipated in the nanocrystal due to hot-carrier relaxation. © 2010 The American Physical Societ

Anomalous power laws of spectral diffusion in quantum dots: A connection to luminescence intermittency

We show that the wandering of transition frequencies in colloidal quantum dots does not follow the statistics expected for ordinary diffusive processes. The trajectory of this anomalous spectral diffusion is characterized by a root t dependence of the squared deviation. The behavior is reproduced when the electronic states of quantum dots are assumed to interact with environments such as, for example, an ensemble of two-level systems, where the correlation times are distributed according to a power law similar to the one generally attributed to the dot's luminescence intermittency