The role of defect interactions in reducing the decay time of H3 luminescence in diamond

Cathodoluminescence in Ultrafast Electron Microscopy

Implementing the modern technologies of light-emitting devices, light harvesting, and quantum information processing requires the understanding of the structure-function relations at spatial scales below the optical diffraction limit and time scales of energy and information flows. Here, we distinctively combine cathodoluminescence (CL) with ultrafast electron microscopy (UEM), termed CL-UEM, because CL and UEM synergetically afford the required spectral and spatiotemporal sensitivities, respectively. For color centers in nanodiamonds, we demonstrate the measurement of CL lifetime with a local sensitivity of 50 nm and a time resolution of 100 ps. It is revealed that the emitting states of the color centers can be populated through charge transfer among the color centers across diamond lattices upon high-energy electron beam excitation. The technical advance achieved in this study will facilitate the specific control over energy conversion at nanoscales, relevant to quantum dots and single-photon sources.

Brilliant blue, green, yellow, and red fluorescent diamond particles: synthesis, characterization, and multiplex imaging demonstrations

Until recently, the number of emission colors available from fluorescent diamond particles was primarily limited to red to near-infrared fluorescence from the nitrogen-vacancy color center in type Ib synthetic diamond and green fluorescence associated with the nitrogen-vacancy-nitrogen center in type Ia natural diamond. Using our recently reported rapid thermal annealing technique, we demonstrate the capability of producing fluorescent diamond particles that exhibit distinctive blue, green, yellow, and red fluorescence from the same synthetic diamond starting material. Utilizing these multiple colored diamonds, we analyze their fluorescence characteristics both in-solution as well as on-substrate and additionally evaluate their viability in simple multiplex imaging and cellular bioimaging experiments. While there are still challenges associated with their immediate use in traditional multiplex imaging, this novel approach opens new opportunities to enhance the capability and flexibility of fluorescent diamond particles at the nanoscale.

Enrichment of ODMR-active nitrogen-vacancy centres in five-nanometre-sized detonation-synthesized nanodiamonds: Nanoprobes for temperature, angle and position

The development of sensors to estimate physical properties, and their temporal and spatial variation, has been a central driving force in scientific breakthroughs. In recent years, nanosensors based on quantum measurements, such as nitrogen-vacancy centres (NVCs) in nanodiamonds, have been attracting much attention as ultrastable, sensitive, accurate and versatile physical sensors for quantitative cellular measurements. However, the nanodiamonds currently available for use as sensors have diameters of several tens of nanometres, much larger than the usual size of a protein. Therefore, their actual applications remain limited. Here we show that NVCs in an aggregation of 5-nm-sized detonation-synthesized nanodiamond treated by Krüger's surface reduction (termed DND-OH) retains the same characteristics as observed in larger diamonds. We show that the negative charge at the NVC are stabilized, have a relatively long T₂ spin relaxation time of up to 4 μs, and are applicable to thermosensing, one-degree orientation determination and nanometric super-resolution imaging. Our results clearly demonstrate the significant potential of DND-OH as a physical sensor. Thus, DND-OH will raise new possibilities for spatiotemporal monitoring of live cells and dynamic biomolecules in individual cells at single-molecule resolution.

Superresolution Microscopy of Single Rare-Earth Emitters in YAG and H3 Centers in Diamond

We demonstrate superresolution imaging of single rare-earth emitting centers, namely, trivalent cerium, in yttrium aluminum garnet crystals by means of stimulated emission depletion (STED) microscopy. The achieved all-optical resolution is ≈50  nm. Similar results were obtained on H3 color centers in diamond. In both cases, STED resolution is improving slower than the conventional inverse square-root dependence on the depletion beam intensity. In the proposed model of this effect, the anomalous behavior is caused by excited state absorption and the interaction of the emitter with nonfluorescing crystal defects in its local surrounding.

Luminescence lifetimes of neutral nitrogen-vacancy centres in synthetic diamond containing nitrogen

The decay time of luminescence from neutral nitrogen-vacancy (NV(0)) centres in synthetic diamond is reported. The intrinsic luminescence lifetime of NV (0) is measured as τ(r) = 19 ± 2 ns. Neutral substitutional nitrogen atoms (N(S)(0)) are shown to quench luminescence from NV(0) by dipole-dipole resonant energy transfer at a rate such that the transfer time would equal τ(r) if one (N(S)(0)) atom was ~3 nm from the NV(0). In chemical-vapour-deposited diamonds grown with a small nitrogen content, that are brown as a result of vacancy-cluster defects, the decay time of NV(0) equals τ(r) in the as-grown material. However, after annealing at ≥1700 °C to remove the brown colour, luminescence from the NV(0) centres is severely quenched. This effect is suggested to be a result of the destruction of NV(0) centres and the creation of new NV(0) centres localized in vacancy-rich regions of the crystals.

Luminescence-lifetime mapping in diamond

This paper introduces a new technique to the study of diamonds: mapping the luminescence lifetime of optical centres. The understanding of luminescence lifetimes in diamond is briefly reviewed. Since lifetime mapping involves extended measuring times with focused laser excitation, the stability of the H3 optical centre is investigated. We show that saturation of the H3 luminescence requires excitation power densities in excess of 10 MW cm(-2). The non-radiative energy transfer time from an H3 centre to an A aggregate is found to be equal to that from N3 centres to A aggregates, at ∼3 × 10(-16)r(8) s, where there are r bond lengths between the H3 and A centres. Non-radiative energy transfer is shown to occur from the NV(-) band to the single substitutional nitrogen atoms: the single N atoms may quench luminescence as well as the A aggregates of nitrogen. In contrast, a comparison of the decays from the very similar H3 and H4 centres demonstrates that the B aggregate produces very weak quenching of the visible luminescence from diamond.

Bright Fluorescent Nanodiamonds: No Photobleaching and Low Cytotoxicity

Diamond nanocrystals emit bright fluorescence at 600-800 nm after irradiation by a 3 MeV proton beam (5 x 1015 ions/cm2) and annealing at 800 degrees C (2 h) in vacuum. The irradiation/annealing process yields high concentrations of nitrogen-vacancy defect centers ( approximately 107 centers/mum3), making possible visualization of the individual 100 nm diamond crystallites using a fluorescence microscope. The fluorescent nanodiamonds (FND) show no sign of photobleaching and can be taken up by mammalian cells with minimal cytotoxicity. The nanomaterial can have far-reaching biological applications.

On topographically identifiable sources of cathodoluminescence in natural diamonds

An extensive examination of the cathodoluminescent emissions from natural diamonds has been performed with due regard to their inhomogeneity, correlating cathodoluminescence properties point-by-point with the local crystal lattice texture and imperfection content as revealed by other topographic techniques (in particular X-ray topography). Some dozens of crystals have been examined, mainly prepared in the form of cut and polished sections but in some cases as whole stones in their natural state. The cathodoluminescence observations have been made by visual microscopy, by photomicrography, and by 'spectrum topography’ with spatial resolution down to 5 pm. Particular attention was devoted to those crystals, not uncommon, whose growth stratigraphy included 2ones of type II (ultraviolet-transmitting) diamond intercalated within regions of the more usual type la (ultraviolet-absorbing) diamond. These type II zones prove to be particularly rich in fine structure within their patterns of cathodoluminescent emission, and in the spectral variety of their emissions. Joint cathodoluminescence topographic and X-ray topographic examinations were made on all specimens. Where feasible, the specimens were also characterized by ultraviolet transmission topographs, and by topographic recording of the anomalous spike diffuse X-ray reflexions. Many cathodoluminescence emissions (including both well-known and littleknown spectral systems) were discovered to have clearly defined topographically localized sources, e.g. dislocation lines or regions which had sustained natural a-particle irradiation. Some findings among many of this nature which are set out in detail concern the emission system (known as H3) which has zero phonon line at 2.46 eV and strong coupling to phonons of 40 meV energy. Its sources include curvilinear growth bands in regions where crystal growth has been of non-faceted, ‘cuboid’ habit rather than of the usual {111} faceted habit, slip traces and individual dislocation lines in matrices of type II character, and occasionally, in similar matrices, (lOO)-orientation platelets ranging from ca. 1 pm to several tens of micrometres in diameter. The H3 system emission from the platelets is more than 90 % linearly polarized with E vector in the platelet plane. (These platelets also emit in the near infrared, at energies of ca. 1.25 eV.) Another emission system with zero phonon line at 2.46 eV, but with only weak phonon coupling (dominant phonon energy ca. 66 meV), was found solely in emissions from the natural radiation-damaged rinds of diamonds, or from patches of natural radiation damage on their external surfaces. Noteworthy is the occurrence of dislocations blue-emitting and of dislocations emitting the H3 system in close juxtaposition within type II matrices. The deep blue broad-band spectral emission from dislocations is strongly polarized with E vector parallel to the dislocation line. The H3 system emission from dislocations is unpolarized. In dislocation-rich type II crystals possessing a mosaic texture the blue emission from dislocations is the dominant source of visible cathodoluminescence at room temperature. Evidence bearing upon the relation of the visible {100} platelets to the submicrometre size {100} platelets which give rise to the anomalous ‘spike’ diffuse X-ray reflexions is examined: as far as their X-ray diffracting properties show, they are indistinguishable.

The decay time of N3 luminescence in natural diamond

Measurements are reported of the decay time of photoluminescence from the N3 centre: an impurity centre commonly found in natural diamond. The intrinsic decay time at low temperature is found to be 41 ± 1 ns. The decay time is specimen dependent, decreasing with increasing concentrations of pairs of substitutional nitrogen atoms in the diamonds. The data are consistent with an electric dipole, electric-quadrupole coupling of the N3 centres to the nitrogen pairs. In addition, the decay time is reduced by raising the specimen temperature, especially above 450 K. These results are consistent with internal conversion occurring into another excited electronic state of the N3 centre. The properties required for this state agree with deductions from other optical and electron paramagnetic resonance (e. p. r.) data. The radiative lifetime of the N3 luminescence transition is estimated at 150 ns, in agreement with previous luminescence efficiency measurements.