Fluorescent Microdiamonds
Fluorescent diamond micropartices offer the highest fluorescence intensity. The fluorescence of these particles can be directly observed with a UV lamp, particularly with short wave UV (ca. 254 nm). This is distinct from nanosized particles, where significant light scattering inhibits the observation of fluorescence without optical filters. Adámas offers microdiamond particles in sizes ranging from 1 um up to 850 um. Across this size range, particles engineered to have different emission wavelengths are available, including: blue fluorescence from N3 centers, green fluorescence from nitrogen-vacancy-nitrogen (NVN) centers, red fluorescence from nitrogen-vacancy (NV) centers, particles with mixtures of different color centers, and microdiamond particles with near-IR emitting silicon-vacancy (SiV) centers . The high brightness, photostability, chemical and mechanical robustness, and unique spectroscopic fingerprints of fluorescent microdiamonds can be utilized in quantum sensing, anticounterfeiting, fluid tracing, fluorescent paints, forensics, bioimaging, extreme environment sensing, and energy applications (e.g., photovoltaics).
Technical Characteristics
Microdiamond Particles with NV or NVN centers (750 nm – 150 µm)
Adámas offers fluorescent microparticles with a range of sizes: 1 μm (approx. 750 nm volumetric peak via dynamic light scattering (DLS) (Figure 1 and Figure 2), 3 μm, 15 μm (Figure 3), 40 μm (Figure 4b) and 150 μm (Figure 3 and Figure 4a). Diamond particles with red emission are enriched with NV centers, while particles with green emission are enriched with NVN centers.
Figure 1. Typical volumetric size distribution for 1 um fluorescent microdiamond particles in water measured with dynamic light scattering.
Particles with SiV centers : 1 µm
High Pressure-High Temperature synthesized (HPHT) diamond particles enriched with silicon-vacancy centers are available in limited amounts. The particles are nominally 1 µm in size, and are provided in water at 0.5 mL. For additional technical details on these particles, see our publication in Advanced Optical Materials (2020): Near-Infrared Fluorescence from Silicon- and Nickel-Based Color Centers in High-Pressure High-Temperature Diamond Micro- and Nanoparticles.
(NEW!) Blue Fluorescent Microdiamonds : 15 - 25 µm
Adámas offers 15-25 micron particles with blue fluorescence due to N3 Centers (Figure 8a-b) from starting synthetic, HPHT type 1b particles. The particles containing N3 centers are uniquely spectrally purified from other color centers (Figure 8b), resembling natural diamond. Due to the presence of Ni catalysts during growth of HPHT diamond, a fraction of particles emits green light with a corresponding spectra of Ni-related centers (Figure 8a,c). Particles have carboxylic groups on their surface and are sold in powder form.
Figure 8. (a) Fluorescence image taken with mercury lamp excitation. Edge filter 450 nm. (b) Emission spectra from blue particles in (a) taken with mercury lamp excitation and edge filter 420 nm. (c) Emission spectra from green particles in (a) taken with mercury lamp excitation and edge filter 420 nm.
Figure 2. Water suspensions of 1 um fluorescent particles with NV centers in quartz cuvettes under different excitation conditions on a UV lamp.
Figure 4. Fluorescence micrographs of 150 μm particles containing NV centers under green excitation (517 nm/20 nm filter)(a) and 40 μm particles with NVN centers under blue excitation (470 nm/28 nm filter) (b). Absorption (dashed lines) and fluorescence emission (solid lines) spectra for NV- and NVN centers (c)
Typical absorption and emission profiles for NV and NVN centers are shown in Figure 4c. Particles with green luminescence centers are available either from natural diamonds or from synthetic diamonds (formed by high temperature annealing). Absorption extends into the UV region. The distinction between the negatively charged NV(-) and neutral NV(0) centers becomes quite noticeable. The NV(0) center can absorb photons all the way to ~250 nm and below, with a possibility of excitation across the band gap. Because the absorption spectra of NV(0) and NV(-) overlap, it is possible for the NV(0) center to excite the NV(-) center. Particles containing higher amounts of NV(0) will exhibit strong fluorescence under both long-wave UV (LWUV, ~365 nm) and short-wave UV (SWUV, ~254 nm) (Figure 3). High fluorescence can be observed under SWUV, where simultaneous excitation of NV(-) via NV(0) is observed. NV(-) concentrations are typically on the order of 2-3 ppm based on electron paramagnetic resonance (EPR) characterization. 1 µm and larger particles are provided with primarily amphoteric surface functional groups (carboxylic acids, alcohols, etc.), but carboxylic acid enriched variants are available. Other functionalized products, such as streptavidin and biotin, are also available. Microparticles (except 1 µm and 3 µm) are typically provided as a powder/grit as they lack long term colloidal stability in solution due to their larger sizes.
Figure 5. Microdiamond particles with NV centers across three different size ranges.
Figure 7. (a) Rabi oscillation trace recorded for the a’ line in Figure 6b. A four component exponentially damped cosine fit (red trace) is shown with fitted relaxation components listed. The first two relaxation components dominate the trace. (b) T1 relaxation trace with stretched exponential fit with stretching parameter (ρ = 0.908).
Figure 3. Fluorescence emission of 150 μm and 15 μm fluorescent diamond particles under SWUV (254 nm) and LWUV (365 nm) generated by a UV blacklight.
The largest particles currently available containing NV centers are up to 0.85 µm in size (Figure 5). These particles are large enough to be manipulated individually with tweezers. Additional characterization of these particles, including ODMR spectra, T1 relaxation, and Rabi oscillation measurements are shown in Figure 6 and Figure 7.
Figure 6. Continuous wave ODMR spectra measured under zero magnetic field conditions (a) and under an applied bias magnetic field (b). In (a), a two-component Lorentzian fit (thin red line) is shown along with microwave power and fit parameters. D is the zero field splitting parameter, E is the strain parameter, and W1 and W2 are the fitted peak widths for each component. In (b), pairs of peaks corresponding to particular NV- orientations are labeled.
