Photoluminescence from NV− Centres in 5 nm Detonation Nanodiamonds: Identification and High Sensitivity to Magnetic Field
Vladimir Yu. Osipov, François Treussart, Soroush Abbasi Zargaleh, Kazuyuki Takai, Fedor Mikhailovich Shakhov, Benjamin Thomas Hogan, Anna V. Baldycheva
The content of nitrogen-vacancy (NV − ) colour centres in the nanodiamonds (DNDs) produced during the detonation of nitrogen-containing explosives was found to be 1.1 ± 0.3 ppm. This value is impressive for nanodiamonds of size < 10 nm with intentionally created NV − centres. The concentration was estimated from the electron paramagnetic resonance as determined from the integrated intensity of the g = 4.27 line. This line is related with “forbidden” ∆ m s = 2 transitions between the Zeeman levels of a NV − centre’s ground triplet state. Confocal fluorescence microscopy enables detection of the red photoluminescence (PL) of the NV − colour centres in nanoscale DND aggregates formed from the 5-nm nanoparticles. Subwavelength emitters consisting of NV − with sizes a few times smaller than the diffraction-limited spot are clearly distinguished. We have further observed an abrupt drop in the PL intensity when mixing and anti-crossing of the ground and excited states spin levels in NV − occurs under an applied external magnetic field. This effect is a unique quantum feature of NV − centres, which cannot be observed for other visible domain light-emitting colour centres in a diamond lattice.
The content of nitrogen-vacancy (NV − ) colour centres in the nanodiamonds (DNDs) produced during the detonation of nitrogen-containing explosives was found to be 1.1 ± 0.3 ppm. This value is impressive for nanodiamonds of size < 10 nm with intentionally created NV − centres. The concentration was estimated from the electron paramagnetic resonance as determined from the integrated intensity of the g = 4.27 line. This line is related with “forbidden” ∆ m s = 2 transitions between the Zeeman levels of a NV − centre’s ground triplet state. Confocal fluorescence microscopy enables detection of the red photoluminescence (PL) of the NV − colour centres in nanoscale DND aggregates formed from the 5-nm nanoparticles. Subwavelength emitters consisting of NV − with sizes a few times smaller than the diffraction-limited spot are clearly distinguished. We have further observed an abrupt drop in the PL intensity when mixing and anti-crossing of the ground and excited states spin levels in NV − occurs under an applied external magnetic field. This effect is a unique quantum feature of NV − centres, which cannot be observed for other visible domain light-emitting colour centres in a diamond lattice.
Group-IV color centers in diamonds are promising not only as spin-photon interfaces for quantum networks but also as multicolor photoluminescence probes and all-optical temperature sensors for biological research. Therefore, generating group-IV color centers in detonation nanodiamonds (DNDs), the smallest class of diamond nanocrystals, has become a research focal point. This approach holds potential for the noninvasive introduction of diamond sensors into living cell organelles, enabling sensing of local structural and temperature changes with minimal disturbance. Following the successful generation of silicon- and germanium-vacancy centers in DNDs, the generation of tin-vacancy (SnV) centers was investigated. Similar to other group-IV color centers, the SnV centers exhibit strong photoluminescence. In addition, the SnV center offers a long spin coherence time compared with those of silicon- and germanium-vacancy centers. However, the strain induced by large Sn atoms poses substantial challenges for generating SnV centers in ultrasmall nanodiamonds. In this study, Sn-doped DNDs with a mean particle size of ~ 5 nm were subjected to a 3 days boiling acid treatment, which led to sharp zero-phonon lines of SnV centers at ~ 620 nm in the photoluminescence spectra. Photon autocorrelation measurements further revealed the presence of single SnV centers in these DNDs.
Nitrogen–vacancy (NV) colour centres in diamond are attractive fluorescence emitters owing to their unprecedented photostability and superior applicability to spin manipulation and sub-diffraction far-field optical microscopy. However, some applications are limited by the co-occurrence of dark state population and optical excitation. In this paper, we use fluorescence microscopy and correlation spectroscopy on single negatively charged NV centres in type IIa bulk diamond to unravel the population kinetics of a >100 s long-lived dark state. The bright–dark state interconversion rates show a quadratic dependence on the applied laser intensity, which implies that higher excited states are involved. Depopulation of the dark state becomes less effective at wavelengths above 532 nm, resulting in a complete fluorescence switch-off at wavelengths >600 nm. This switch is reversible by the addition of shorter wavelengths. This behaviour can be explained by a model consisting of three dark and three bright states of different excitation levels, with the most efficient interconversion via the respective higher excited states. This model accounts for the nonlinear dark state and photoswitching kinetics, as well as for the decrease of the NV's fluorescence lifetime with excitation intensity and the strong dependence of fluorescence emission on excitation intensity. Unfortunately, our data do not give enough insight to allow us to assign the different states to specific electronic states known from the literature. Nevertheless, our observations allowed us to improve the recording of fluorescence images of single NV centres with sub-diffraction spatial resolution but they also have important implications for studying their spin states.
Abstract The nitrogen-vacancy colour centre in diamond is emerging as one of the most important solid-state quantum systems. It has applications to fields including high-precision sensing, quantum computing, single photon communication, metrology, nanoscale magnetic imaging and biosensing. For all of these applications, a high quantum yield of emitted photons is desirable. However, diamond samples engineered to have high densities of nitrogen-vacancy centres show levels of brightness varying significantly within single batches, or even within the same sample. Here we show that nearby nitrogen impurities quench emission of nitrogen-vacancy centres via non-radiative transitions, resulting in a reduced fluorescence quantum yield. We monitored the emission properties of nitrogen-vacancy centre ensembles from synthetic diamond samples with different concentrations of nitrogen impurities. All samples were irradiated with high energy electrons to create high densities of nitrogen-vacancy centres relative to the concentration of nitrogen impurities. While at low nitrogen densities of 1.81 ppm we measured a lifetime of 13.9 ns, we observed a strong reduction in lifetime with increasing nitrogen density. We measure a lifetime as low as 4.4 ns at a nitrogen density of 380 ppm. The change in lifetime matches a reduction in relative fluorescence quantum yield from 77.4% to 32% with an increase in nitrogen density from 88 ppm to 380 ppm, respectively. These results will inform the conditions required to optimise the properties of diamond crystals devices based on the fluorescence of nitrogen-vacancy centres. Furthermore, this work provides insights into the origin of inhomogeneities observed in high-density nitrogen-vacancy ensembles within diamonds and nanodiamonds.
Diamond nanocrystals containing highly photoluminescent color centers are attractive, nonclassical, and near-field light sources. For near-field applications, the size of the nanocrystal is crucial, since it defines the optical resolution. Nitrogen-vacancy (NV) color centers are efficiently created by proton irradiation and annealing of a nanodiamond powder. Using near-field microscopy and photon statistics measurements, we show that nanodiamonds with sizes down to 25 nm can hold a single NV color center with bright and stable photoluminescence.
The NV defect center in diamond forms a pseudo-atomic quantum system with discreet optically excitable transitions between ground and excited states in the gap between valence and conduction bands, making the NV center a deep-level defect center in diamond. For the negatively charged NV center (NV-), both the ground and excited states are spin triplets (S=1) and coupling between optical and spin states provides unique opportunities for optical detection of magnetic resonance (ODMR) and quantum metrology under ambient conditions. As an atomically sized point defect that is stable in single nanodiamonds as small as a few nanometers, the NV center enables spin based imaging of temperature, electric fields, magnetic fields and mechanical strain with nanoscale spatial resolution. Made of carbon, nanodiamonds are also ideal nanoparticles for use in biological systems, exhibiting extremely low cytotoxicity, no photo bleaching and exceptional contrast in transmission electron and light microscopy. With the ability to act as both a passive, non perturbing sensor (e.g. a diamagnetic material used for sensing magnetic fields) and a connection point for two way, direct coupling of far field optics to NV− spins and indirectly to the highly localized neighborhood of atoms, electronic states and phonon modes in the local vicinity, NV diamond provides a route to nanoscale field sensing and spin based optical microscopy. These sensors are also stable in nanodiamonds. For nanoparticles, the reduction in particle diameter dramatically enhances the proportion of the material that is surface exposed, enhancing any surface related properties. Nitrogen Vacancy centers in nanodiamonds provide another example of material properties that vary with particle size. In chapter 5, evidence that modulation of nanodiamonds fluorescent emissions by electrical perturbations in their surrouding environment allows transduction of local electrodynamics into a far field optical signal capable of mapping action potentials in cardiomyocytes in presented. The unifying theme for all of the work presented in this dissertation is to enable the use of magnetic resonance signals and interactions for imaging and sensing in previously inaccessible regimes. The specific focus is on methods and techniques to enable nanoscale physical sensing and functional imaging in live tissues, with the ultimate aim to lay the predicate for the combination of both without compromise.
The nitrogen-vacancy (NV) centre in diamond is a unique optical defect that is used in many applications today and methods to enhance its fluorescence brightness are highly sought after. We observed experimentally an enhancement of the NV quantum yield by up to 7% in bulk diamond caused by an external magnetic field relative to the field-free case. This observation is rationalised phenomenologically in terms of a magnetic field dependence of the NV excited state triplet-to-singlet transition rate. The theoretical model is in good qualitative agreement with the experimental results at low excitation intensities. Our results significantly contribute to our fundamental understanding of the photophysical properties of the NV defect in diamond.