Method for separating or concentrating ND particles containing lattice defects

Abstract

This invention provides a highly efficient method for separating or concentrating lattice defect-containing nanoparticles (NDs). [Solution] A method for separating or concentrating lattice defect-containing ND particles, comprising irradiating a dispersion containing at least two types of ND particles selected from nanodiamond (ND) particles having at least one type of lattice defect and ND particles without the lattice defect with at least one type of excitation laser light having an energy greater than or equal to the resonance absorption energy of the lattice defect and at least one type of stimulated emission laser light, thereby selectively moving the ND particles having the lattice defect by the absorption optical pressure generated by the absorption of at least one type of excitation laser light and the stimulated recoil force generated by the action of at least one type of stimulated emission laser light, wherein the excitation laser light transitions electrons in the ground state of the ND particles to an excited state, and the stimulated emission laser light transitions electrons in the excited state to the ground state faster than spontaneous emission to generate stimulated recoil force.

Description

Technical Field

[0001] The present invention relates to a method for separating or concentrating nanodiamond (ND) particles having lattice defects.

[0002] In this specification, the following abbreviations may be used. ND: Nanodiamond NV: Nitrogen-vacancy SiV: Silicon-vacancy GeV: Germanium-vacancy SnV: Tin-vacancy PbV: Lead-vacancy NiV: Nickel-vacancy

Background Art

[0003] A method for sorting fluorescent nanodiamond particles having NV centers in a glass capillary using light pressure is known (Patent Document 1), but the sorting efficiency was not sufficient.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The main object of the present invention is to provide a method for separating or concentrating lattice defect-containing ND particles with high efficiency.

Means for Solving the Problems

[0006] The present invention provides a method for separating or concentrating the following lattice defect-containing ND particles. [1] A method for separating or concentrating lattice defect-containing ND particles, comprising irradiating a dispersion containing at least two types of ND particles selected from nanodiamond (ND) particles having at least one type of lattice defect and ND particles without the lattice defect with at least one type of excitation laser light having an energy greater than or equal to the resonance absorption energy of the lattice defect and at least one type of stimulated emission laser light, thereby selectively moving the ND particles having the lattice defect by the absorption optical pressure generated by the absorption of at least one type of excitation laser light and the stimulated recoil force generated by the action of at least one type of stimulated emission laser light, wherein the excitation laser light transitions electrons in the ground state of the ND particles to an excited state, and the stimulated emission laser light transitions electrons in the excited state to the ground state faster than spontaneous emission to generate stimulated recoil force. [2] A method for separating or enriching ND particles having the lattice defect described in [1], wherein the lattice defect is one selected from the group consisting of NV centers, SiV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, NE8 centers, and P1 centers. [3] A method for separating or enriching ND particles having the lattice defect described in [1], wherein the lattice defect is one selected from the group consisting of NV centers, SiV centers, GeV centers, and P1 centers. [4] A method for separating or concentrating ND particles having lattice defects as described in [1], comprising irradiating excitation laser light and stimulated emission laser light in opposing directions. [5] A method for separating or concentrating ND particles having lattice defects as described in [1], wherein the dispersion is contained in a container having two capillaries connected together, and an excitation laser beam and a stimulated emission laser beam are irradiated oppositely to the connecting portion. [Effects of the Invention]

[0007] According to the present invention, ND particles having lattice defects can be efficiently separated or concentrated by utilizing the optical pressure from excitation laser light. While sorting ND particles with one or several lattice defects by absorption optical pressure is expected to be difficult due to the small size of the ND particles, the present invention enables extremely efficient sorting by using induced recoil force. By separating, concentrating, or selecting ND particles with lattice defects to improve their quality, they can not only be used as fluorescent markers, but also as a collection of high-quality ND particles that can be used in quantum information devices (e.g., hybrid quantum systems). Since stimulated emission laser light emits light faster than spontaneous emission, it not only significantly reduces the effect of absorption saturation of the excitation laser light, but also suppresses the broadening of the spectral width caused by high-intensity excitation laser light. Furthermore, since the emission line of the selected ND particles is determined by the spectrum of the stimulated emission laser light, it is possible to separate, concentrate, or select only ND particles (emitters) with a specific emission line within a narrow width while increasing the optical pressure based on the excitation laser light. [Brief explanation of the drawing]

[0008] [Figure 1-1] (a) Schematic diagram of the experimental setup, (b) Positional relationship between the observation point and the focal point of the optical pressure source laser. [Figure 1-2] Time evolution of ZPL intensities at the SiV and GeV centers at the observation point during laser irradiation for excitation of the optical pressure source. [Figure 2-1] (a) Schematic diagram of the experimental setup, (b) focal points of the opposing excitation laser and stimulated emission laser, and the positional relationship between observation points 1 and 2. All lasers are focused 2 mm from the end face on the side emitting the stimulated emission laser. Observation point 1, located 1 mm from the end face on the side emitting the stimulated emission laser, and observation point 2, located 3 mm from the end face, are observed as fixed points. [Figure 2-2] (a) Time evolution of ZPL intensity at SiV and GeV centers at observation point 1 and (b) observation point 2 [Figure 3-1](a) Level structure of the SiV center and (b) the optical system used. In (b), the excitation laser is directed from the opposite side, and the stimulated emission laser is directed from one side towards the ND. [Figure 3-2] Initial time and position of the SiV-ND within the capillary after irradiation with the excitation laser and stimulated emission laser for 7 hours. [Figure 3-3] Initial time and the position of the undoped ND within the capillary after irradiation with the excitation laser and stimulated emission laser for 7 hours. [Figure 4-1] Optical system. A stimulated emission laser and an excitation laser are directed at each other. [Figure 4-2] Position of the SiV-ND within the capillary at time 0 and after irradiation with the excitation laser and stimulated emission laser for 7 hours. [Figure 4-3] The position of the undoped-ND within the capillary at time 0 and after irradiation with the excitation laser and stimulated emission laser for 7 hours. [Figure 5-1] H-shaped channel of the SiV-ND recovery mechanism (3D diagram). [Figure 5-2] Velocity field inside an H-shaped channel (cross-sectional view). [Figure 5-3] Conceptual diagram of the SiV-ND recovery mechanism. It is connected to two H-shaped capillaries, and the excitation and stimulation light of the SiV-ND are irradiated in opposite directions at the connection point. The black arrow in the upper left does not point to the excitation laser, but to the direction of fluid flow. Therefore, the ND particles are transported by the flow to the connection point, where they are subjected to absorption light pressure and induced recoil force, and then move to the lower capillary. [Figure 5-4] (a) Concentrations of SiV-ND and (b) undoped-ND within the capillary. The lines in the channel indicate concentration contours. In both (a) and (b), the two color bars located on the right of the figure show the concentrations of SiV-ND and undoped-ND on the left and the concentration contour values ​​on the right. The shape of the contour lines is symmetrical in the upper and lower capillaries in (b), whereas it is asymmetrical in (a). This indicates that more SiV-ND is transported to the lower capillary and concentrated there due to absorption pressure and induced recoil compared to undoped-ND. [Figure 6-1] The optical system used in the computational experiment. The excitation laser is irradiated oppositely, and the stimulated emission laser is irradiated onto ND from one direction. However, in the actual calculation, it was assumed that there were 100 NDs each at the origin at the initial time. [Figure 6-2] The positions of SiV-NDs after irradiating the excitation CW laser (1.714 eV) oppositely and irradiating the stimulated emission CW laser (1.681 eV) in the positive z-axis direction for 1 hour. [Figure 6-3] The positions of SiV-NDs after irradiating the excitation pulsed laser (1.714 eV) oppositely and irradiating the stimulated emission pulsed laser (1.681 eV) in the positive z-axis direction for 1 hour. [Figure 7] The optical pressure using the induced recoil force. [Figure 8] The structures of the NV center, SiV center, GeV center, and P1(Ns) center.

Modes for Carrying Out the Invention

[0009] The particles to which the method of the present invention is applied are mixed particles of at least two types of ND particles, including ND particles having at least one type of lattice defect and at least one type of ND particle without the lattice defect. A dispersion containing the mixed particles in a solvent is irradiated with at least one excitation laser beam having an energy equal to or greater than the resonance absorption energy (e.g., NV center, SiV center, GeV center, SnV center, PbV center) or absorption energy (e.g., in the case of a P1 center) of the at least one type of lattice defect, and at least one stimulated emission laser beam that promotes the stimulated emission of electrons relaxed from the excited level that absorbed the excitation laser beam to a lower emission level. When irradiated with excitation laser beam, the ND particles to be separated or concentrated that absorb the excitation laser beam selectively move in the direction of the laser beam's propagation due to the absorption light pressure generated by absorbing the laser beam, and no absorption light pressure is generated for ND particles that do not absorb the laser beam and are not to be separated or concentrated, based on the absorption of the excitation laser beam. Furthermore, as a result of the combination of the stimulated recoil force associated with stimulated emission and the absorption light pressure, lattice defect-containing ND particles are efficiently separated or concentrated. Because the stimulated recoil force maintains a narrow linewidth even when the incident light intensity is increased, it is possible to select ND particles with close emission lines. Furthermore, it is preferable to adjust and match the intensities of the excitation laser light and the stimulated emission laser light. When a particle is in a population inversion state, stimulated emission occurs, generating light emission and thus a recoil force. In this specification, this force is referred to as the stimulated recoil force. By using the stimulated recoil force, it becomes possible to select ND particles according to their emission lines. Electrons in the excited state transition to the ground state much faster than spontaneous emission due to the stimulated emission laser light, generating a stimulated recoil force. Therefore, the stimulated emission laser light significantly reduces the effects of absorption saturation and also suppresses the broadening of the spectral width due to high-intensity excitation light. As a result, it becomes possible to select emitters (ND particles) with very narrow emission lines.

[0010] In this specification, lattice defects include NV centers, SiV centers, GeV centers, SnV centers, PbV centers, P1 centers, NiV centers, H3 centers, NE8 centers, and the like, preferably NV centers, SiV centers, GeV centers, SnV centers, PbV centers, and P1 centers, and more preferably NV centers, SiV centers, GeV centers, and P1 centers.

[0011] Solvents for preparing dispersions include water, C1-C6 alcohols such as ethanol, methanol, isopropanol, and butanol, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ethers such as diethyl ether and diisopropyl ether, acetate esters such as methyl acetate and ethyl acetate, halogenated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride, aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as hexane, alicyclic hydrocarbons such as cyclohexane, tetrahydrofuran, acetonitrile, dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. These solvents can be used individually or in combination of two or more.

[0012] As shown in Figure 7, when excitation laser light matching the resonance absorption energy of ND particles having lattice defects to be separated is irradiated onto the ND particles, an absorption light pressure (resonant absorption force) is generated due to resonance absorption, and the light pressure is maximum in this case. When a laser with a higher energy than the resonance absorption energy of the ND particles is irradiated onto the ND particles, resonance does not occur, but an absorption light pressure based on the absorption force is generated, thereby enabling the optical pressure separation of the ND particles to be separated. Here, the absorption light pressure for separation or concentration is maximum when the ND particles are irradiated with a laser matching the resonance absorption energy (absorption light pressure based on resonance absorption force), and is greater than the absorption force generated when the ND particles are irradiated with a laser with a higher energy than the resonance absorption energy of the ND particles, enabling more efficient separation of the ND particles. Therefore, a laser matching the resonance absorption energy is most preferable, and a laser with a higher energy than the resonance absorption energy can generate an absorption light pressure of sufficient magnitude for the separation or concentration of ND particles. The maximum energy of a laser that is higher than the resonant absorption energy is not particularly limited, but is, for example, 4 eV, preferably 3 eV.

[0013] Furthermore, since the P1 center has no resonant absorption energy, it is sufficient to irradiate it with laser light equal to or greater than its absorption energy. The NV, SiV, GeV, SnV, PbV, NiV, H3, and NE8 centers each have their own resonant absorption energy, so it is sufficient to irradiate the ND particles with excitation laser light equal to or greater than their respective resonant absorption energy.

[0014] Furthermore, it has been confirmed that the lattice defect-containing ND particles used in this invention do not fade even when sorted by prolonged irradiation with high-intensity laser light.

[0015] ND particles having at least one type of lattice defect absorb at least one type of excitation laser light and move to the excited level. Below the excited level, the emission level is affected by stimulated emission laser light, which significantly shortens the cycle lifetime time in the transition to emission (stimulated emission) to the ground state, thereby suppressing the saturation of the absorption light pressure due to the excitation laser light. As a result, the absorption light pressure used for the separation or enrichment of ND particles with lattice defects becomes larger, and the separation or enrichment of ND particles can be made more efficient. The stimulated emission laser light is preferably a laser with the energy that best promotes stimulated emission.

[0016] The concentration of ND mixed particles in the dispersion is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass.

[0017] The temperature of the dispersion when irradiated with laser light is preferably 5 to 60°C, more preferably 15 to 35°C.

[0018] In one preferred embodiment of the present invention, the ND particles to be separated or concentrated contain at least one lattice defect selected from NV centers, SiV centers, GeV centers, SnV centers, PbV centers, and P1(Ns) centers. The P1 center takes the form of nitrogen incorporated at the carbon substitution position. Figure 8 shows the structures of the NV center, SiV center, GeV center, and P1(Ns) center.

[0019] Examples of containers for the dispersion include elongated containers such as capillaries. In the case of such an elongated container, by irradiating the excitation laser beam along the longitudinal direction of the container from one end, the ND particles to be separated or concentrated move towards the opposite end along the direction of the laser beam's propagation due to the absorption light pressure generated by the resonant absorption of the laser beam, and are separated or concentrated. If the container for the dispersion is an H-shaped container in which two capillaries are connected in an H-shape, and assuming that the dispersion is flowing in a velocity field along the longitudinal direction of the capillaries, when the ND particles to be separated move to the H-shaped connection, they can be moved to the other capillary by irradiating the H-shaped connection with the excitation laser beam and stimulated emission laser beam opposite each other. By changing the direction of propagation of the excitation laser beam and stimulated emission laser beam (especially making them perpendicular to each other), the separation or concentration of the desired ND particles can be performed more efficiently.

[0020] The absorption pressure based on the excitation laser light acts as a force in the direction of propagation of the excitation laser light, while the stimulated recoil force based on the stimulated emission laser light acts in the opposite direction to the direction of propagation of the stimulated emission laser light. Therefore, in one preferred embodiment of the present invention, the excitation laser light and the stimulated emission laser light are irradiated in opposing directions. Furthermore, in an H-shaped channel as shown in Figure 5-3, the stimulated emission laser light can be irradiated onto the connecting portion in the direction opposite to the direction in which the ND particles are to be moved.

[0021] ND particles not subject to separation or enrichment may contain at least one type of lattice defect. For example, if the ND particles subject to separation or enrichment are ND particles having SiV centers, the ND particles not subject to separation or enrichment may be ND particles without lattice defects, and may contain at least one type of lattice defect other than SiV centers, such as NV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, NE8 centers, and P1(Ns) centers. Furthermore, the ND particles subject to separation or enrichment may have any combination of two types of lattice defects, such as SiV centers and NV centers, SiV centers and P1 centers, GeV centers and NV centers, or GeV centers and P1 centers, or any combination of three types of lattice defects, such as SiV centers, NV centers and P1 centers, or GeV centers, NV centers and P1 centers.

[0022] In the above, the case in which the ND particles to be separated or concentrated have SiV centers was described, but the same separation or concentration can also be performed when the ND particles to be separated or concentrated have NV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, NE8 centers, or P1(Ns) centers, or when they have two, three, or four types, preferably two or three types, of lattice defects. Among the ND particles having NV centers, SiV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, NE8 centers, and P1(Ns) centers, ND particles with lattice defects that have a larger dipole moment than NV centers (SiV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, and NE8 centers), in particular ND particles having SiV centers, generate a large optical pressure and have a greater sorting effect. The mixed particles to which the method of the present invention is applied contain, when the total amount of mixed particles is 100% by mass, 1 ppm to 50% by mass of ND particles to be separated or concentrated, and 50 to 99% by mass or more of ND particles not to be separated or concentrated. By applying the method of the present invention, the proportion of ND particles to be separated or concentrated can be increased, preferably to 1% by mass or more, more preferably to 10% by mass or more, even more preferably to 20% by mass or more, and particularly preferably to 50% by mass or more.

[0023] The resonance absorption energies of lattice defects for laser light are listed below.

[0024] When lattice defects are selected from the group consisting of NV centers, SiV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, and NE8 centers, the resonance absorption energy is a region centered around the listed energies, with energies approximately 10 times the full width at half maximum of the fluorescence peak of each lattice defect on the higher and lower energy sides. Furthermore, the energy of the laser light absorbed by the P1(Ns) center is a region with energies approximately 10% of the reference energy on the higher and lower energy sides, based on the ideal energy difference between the P1(Ns) center and the conductive band of the diamond. Resonance absorption energy of NV centers: 1.91~2.20 eV, especially 1.95 or 2.16 eV. Resonance absorption energy of SiV centers: 1.62~1.75 eV, especially 1.68 eV Resonance absorption energy of GeV centers: 1.94~2.18 eV, especially 2.06 eV Resonance absorption energy of SnV centers: 1.88~2.12 eV, especially 2.00 eV Resonance absorption energy of PbV centers: 2.19–2.42 eV, especially 2.23 or 2.38 eV Absorbed energy of the P1(Ns) center: 1.53~1.87 eV, especially 1.70 eV. Resonance absorption energy of NiV centers: 1.36~1.44 eV, especially 1.40 eV Resonance absorption energy of H3 center: 2.39~2.54 eV, especially 2.4 eV Resonance absorption energy of NE8 center: 1.53~1.59 eV, especially 1.56 eV The energy above the resonant absorption energy of the laser light is 1.91 eV or higher if the ND particle to be separated has an NV center, 1.62 eV or higher if it has an SiV center, 1.94 eV or higher if it has a GeV center, 1.88 eV or higher if it has an SnV center, 2.19 eV or higher if it has a PbV center, and 1.53 eV or higher if it has a P1(Ns) center.

[0025] The energy of the stimulated emission laser light at each lattice defect is shown below. Energy of stimulated emission laser at NV center: 1.91~2.20 eV, especially 1.95 or 2.16 eV. Energy of the stimulated emission laser at the SiV center: 1.62~1.75 eV, especially 1.68 eV. Energy of stimulated emission laser at GeV center: 1.94~2.18 eV, especially 2.06 eV. Energy of the stimulated emission laser at the SnV center: 1.88~2.12 eV, especially 2.00 eV. Energy of stimulated emission laser at PbV center: 2.19~2.42 eV, especially 2.23 or 2.38 eV. Energy of the stimulated emission laser at the P1(Ns) center: 1.53~1.87 eV, especially 1.70 eV. Resonance absorption energy of NiV centers: 1.36~1.44 eV, especially 1.40 eV Resonance absorption energy of H3 center: 2.39~2.54 eV, especially 2.4 eV Resonance absorption energy of NE8 center: 1.53~1.59 eV, especially 1.56 eV The output power of the laser light having the above-mentioned resonance absorption energy is preferably 0.1 to 100 W, and the linewidth is preferably 15 THz or less.

[0026] The laser light irradiation time is preferably 1 to 1000 hours, more preferably 20 to 200 hours.

[0027] Examples of light sources include solid-state lasers such as titanium-sapphire lasers and Nd:YAG lasers, or semiconductor lasers, with titanium-sapphire lasers being preferred.

[0028] The average size of the primary particles of ND is preferably 1 to 100 nm, more preferably 5 to 20 nm. If the average size of the primary particles of ND is within the above range, the target ND particles can be sufficiently separated or concentrated by the optical pressure generated by the resonant absorption of laser light. The average size of the primary particles can be determined from the analysis results of powder X-ray diffraction (XRD) using Scherrer's formula. An example of an XRD measuring device is a fully automated multi-purpose X-ray diffractometer (manufactured by Rigaku Corporation). [Examples]

[0029] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples. Example 1 We attempted to concentrate SiV-ND in a mixture of nanodiamonds containing SiV centers (SiV-ND) and nanodiamonds containing GeV centers (GeV-ND) using resonant optical pressure. SiV-ND and GeV-ND were mixed in a weight ratio of 5 / 1 (SiV-ND / GeV-ND) to prepare an aqueous dispersion with a total ND concentration of 2.5 wt%. This dispersion was packed into a glass capillary with an inner diameter of 20 μm and sealed at both ends with vacuum grease. A continuous-wave (CW) titanium-sapphire laser (Matisse C, Spectra physics) with an energy of 1.68 eV, output of 3.1 W, and linewidth <20 MHz was irradiated from one end of this capillary as an optical pressure source to generate resonant optical pressure in the SiV-ND. The energy of this optical pressure source laser corresponds to the resonant absorption energy of the SiV center. The arrangement of these experimental apparatuses is shown in Figure 1-1(a). The titanium-sapphire laser used as the optical pressure source was excited by a 2.33 eV, 15 W CW laser (Millennia eV, Spectra physics). Subsequently, photoluminescence (PL) measurements were performed on an ND aqueous dispersion in a capillary irradiated with the optical pressure source laser. For the PL measurements, a 2.33 eV CW laser (LCX-532S, Oxxius) was used as the excitation light. The resulting emission was spectrally analyzed using a spectrometer equipped with a 150 gr. / mm diffraction grating (SpectraPro HRS-300, Teledyne Princeton Instruments) and detected by an air-cooled electron multiplying CCD (EMCCD; ProEM+: 16002 eXcelon3, Teledyne Princeton Instruments). The positional relationship between the measurement point and the laser focal point is shown in Figure 1-1(b). The optical pressure source laser was irradiated for 40 hours, during which PL measurements were performed at 15-minute intervals. Figure 1-2 shows the time evolution of the obtained PL spectra, i.e., the intensities of the zero phonon lines (ZPLs) at the SiV and GeV centers observed at 1.68 eV and 2.06 eV, respectively.As shown in Figure 1-2, the ZPL intensity of SiV-ND irradiated with a 1.68 eV laser, which corresponds to the resonance absorption energy, increased over time compared to the ZPL intensity of GeV-ND irradiated with a laser that does not correspond to the resonance absorption energy. These findings indicate enrichment of SiV-ND, with an enrichment of approximately 20% confirmed after 40 hours.

[0030] Example 2 In Example 1, SiV-ND enrichment was performed using resonant optical pressure, but in this example, we attempted to enrich SiV-ND using stimulated recoil, a type of optical pressure. In Example 1, resonant optical pressure was applied to SiV-ND using only an optical pressure source laser, but in this example, stimulated recoil is applied to SiV-ND by inducing stimulated emission after electron excitation of the SiV center. Therefore, this example uses two lasers: an excitation laser and a stimulated emission laser. The arrangement of these experimental apparatuses is shown in Figure 2-1(a). As in Example 1, a 2.5 wt% aqueous dispersion of SiV-ND / GeV-NDs = 5 / 1 (by weight ratio) was filled into a glass capillary with an inner diameter of 20 μm, and both ends were sealed with vacuum grease. As the excitation laser, a continuous-wave (CW) diode-pumped solid-state laser (MGL-N-532Anm-5W-A (Good Beam), CivilLaser) with an energy of 2.33 eV and an output of 3.0 W was used. The excitation laser was split into two 1.5 W beams via a beam splitter, each incident on the capillary from opposite ends. Furthermore, a continuous-wave (CW) titanium-sapphire laser (Matisse C, Spectra physics) with energy 1.6813 eV, power 0.5 W, and linewidth <20 MHz was irradiated from one end of the capillary as a stimulated emission laser. The energy of this stimulated emission laser corresponds to the resonant absorption energy of the SiV center. The stimulated emission titanium-sapphire laser was excited by a CW laser (Millennia eV, Spectra physics) with energy 2.33 eV and power 15 W. Subsequently, PL measurements were performed on the ND aqueous dispersion in the capillary irradiated by the excitation and stimulated emission lasers. For PL measurements, a 2.33 eV CW laser (LCX-532S, Oxxius) was used as the excitation light. The resulting emission was spectrally analyzed using a spectrometer (SpectraPro HRS-300, Teledyne Princeton Instruments) equipped with a 150 gr. / mm diffraction grating, and detected using an air-cooled electron multiplying CCD (EMCCD; ProEM+: 16002 eXcelon3, Teledyne Princeton Instruments).Figure 2-1(b) shows the positional relationship between the measurement point and the focal point of each laser. The excitation laser and stimulated emission laser were irradiated for 7 hours, and PL measurements were taken at intervals of 5 minutes during that time. Figure 2-2(a) shows the time change of the ZPL intensity at observation point 1. The ZPL intensity of SiV-ND decreased by approximately 50% over 7 hours with the laser irradiation time. On the other hand, the ZPL intensity of GeV-ND did not change. Figure 2-2(b) shows the time change of the ZPL intensity obtained at observation point 2. The ZPL intensity at the center of SiV increased with the laser irradiation time, while the ZPL intensity at the center of GeV did not change. From these results, it was confirmed that SiV-ND was selectively transported from observation point 1 to observation point 2, and that it was enriched by approximately 50% over 7 hours. In the selection using stimulated recoil force, the enrichment rate per unit time improved 14 times compared to when using resonant optical pressure.

[0031] Example 3 A computational experiment was conducted to reproduce the experimental results of Example 2. SiV-ND with a particle size of 10 nm was used, and the SiV-ND was modeled as a four-level system as shown in Figure 3-1 (with the levels designated as |1>, |2>, |3>, and |4> in ascending order of energy). For the level structure, vibrational levels were considered for both the ground state and the excited states. Specifically, the transition energies from |1> to |2> and |3> were set to 1.681 eV and 1.714 eV, respectively, and the transition energy from |2> to |3> was set to 1.648 eV. Optical transitions were assumed to occur from |1> to |3> and |4>, with dipole moments of 14.3 Debye and 6.74 Debye, respectively. Furthermore, an optical transition was also assumed to occur from |3> to |2>, with a dipole moment of 7.29 Debye. As relaxation constants for occupancy, the transitions from |4> to |3> and from |2> to |1> were set to 15 meV, and the transitions from |3> to |1> and from |3> to |2> were set to 1.2 μeV. Furthermore, the phase relaxation constant was set to 2 meV, assuming water at room temperature. Assuming that SiV-NDs are uniformly distributed at the initial time, it was assumed that there are 400 of them at 200 μm intervals from -8 mm to 8 mm. The motion of the NDs was evaluated by solving the Langevin equation. The optical pressure acting as an external force was evaluated from the Lorentz force. As for the optical system, as shown in Figure 3-1(b), an excitation laser (output 3 W, energy 1.714 eV) is irradiated in opposition, followed by an irradiated stimulated emission laser (output 0.5 W, energy 1.681 eV), i.e., the same system as in Example 2 is considered. The optical pressure due to resonant absorption saturates above a certain light intensity, but the stimulated recoil force does not saturate, so a force even greater than the resonant absorption force acts. Figure 3-2 shows the position of SiV-ND in the capillary coaxial direction at time 0 and after 7 hours of laser irradiation. From the figure, it can be seen that SiV-ND is transported in the negative z-axis direction. On the other hand, Figure 3-3 shows the results of attempting to enrich ND without SiV centers (undoped-ND) under similar conditions. It can be seen that the effect of optical pressure on undoped-ND is small, and there is almost no difference in the concentration gradient.From the calculation results, in the interval z = -1 mm to -1.2 mm, as shown in Figures 3-2 and 3-3, there are 614 SiV-NDs and 439 NDs that do not contain SiV centers, resulting in an enrichment rate of 40%. This result well reproduces the experimental result of Example 2, in which enrichment was approximately 50% after 7 hours of laser irradiation, and demonstrates the validity of the calculation method.

[0032] Example 4 Based on the confirmation of the validity of the computational experimental method in Example 3, we will consider a SiV-ND enrichment method that combines the resonant optical pressure of Example 1 and the stimulated recoil force of Example 2. As shown in Figure 4-1, we considered a system in which an excitation laser (output 3 W, energy 1.714 eV) and a stimulated emission laser (output 0.5 W, energy 1.681 eV) are irradiated in opposition. In this system, the excitation laser for the stimulated recoil force also serves as the resonant optical pressure source laser. In addition, since neither the stimulated recoil force nor the absorptive force is saturated, the optical pressure that effectively acts on the SiV-ND is the sum of the stimulated recoil force and the unsaturated resonant absorptive force, resulting in a larger optical pressure acting on the SiV-ND compared to Examples 1-3. Figure 4-2 shows the position of the SiV-ND in the coaxial direction of the capillary at time 0 and after 7 hours of laser irradiation, and it can be seen that it is being transported in the positive z-axis direction. On the other hand, Figure 4-3 shows the position of undoped NDs in the capillary coaxial direction in a similar setup, and it can be seen that the effect of optical pressure is small and there is almost no difference in the concentration gradient. From the calculation results, in the interval from z = 1.4 mm to 1.6 mm, as shown in Figures 4-2 and 4-3, there are 681 SiV-NDs and 403 undoped NDs, so the enrichment rate is 69%. In particular, the peak value from z = -1 mm to -2 mm was 614 in the system of Example 3 (Figure 3-2), while it was 681 in the system of this example (Figure 4-2), confirming an 11% improvement in enrichment efficiency due to the improvement of the optical system.

[0033] Example 5 Following the SiV-ND enrichment experiments in Examples 1-4, a recovery mechanism for enriched SiV-ND was investigated. The optical pressure acting on the SiV-ND is the same as in Example 4, the sum of stimulated emission and unsaturated resonance absorption force. In this recovery mechanism, the following flow path is employed. As shown in Figure 5-1, an H-shaped flow path is set up in which two capillaries with an inner diameter of 10 μm × 10 μm are connected by one short capillary (inner diameter in the cylindrical radial direction of 10 μm, axial direction of 4 μm). In this H-shaped flow path, a mixed aqueous dispersion of SiV-ND and undoepd-ND flows in the axial direction of the capillaries in the velocity field shown in Figure 5-2. Furthermore, as shown in Figure 5-3, the excitation laser and stimulated emission laser for the SiV-ND are irradiated in opposition to each other at the connection point, and stimulated recoil force and unsaturated resonance absorption force act on the SiV-ND. The optical intensity densities of the excitation laser and stimulated emission laser are 13 MW / cm², respectively. 2 5.5 MW / cm² 2 Assuming the following, the light pressure is approximately 0.4 fN, so the effective light pressure acting on SiV-ND was estimated to be 0.3 fN. The motion of each ND particle can be determined by solving the advection-diffusion equation. In this mechanism, in the initial state, each ND is present in the upper capillary and is transported axially by the flow field. Upon reaching the connection point, SiV-ND moves to the lower capillary due to light pressure, and undoped-ND moves to the lower capillary due to diffusion. Since the light pressure effect is greater than the diffusion effect, the amount of SiV-ND that moves to the lower capillary is greater, resulting in the enrichment of SiV-ND in the lower capillary. Figures 5-4(a) and (b) show the concentrations of SiV-ND and undoped-ND after a certain period of time, and the lines in the flow path indicate the concentration contours. Converted to a concentration ratio, SiV-ND / undoped-ND is approximately 1.55. That is, enrichment of about 55% was possible. Furthermore, the SiV-ND concentrate can be recovered from the end face of the lower microcapillary.

[0034] Example 6 Because the absorption center energy of SiV-ND differs slightly depending on the ND, in Example 2, only SiV-ND with an absorption energy of 1.6813 eV could be transported and enriched. A system to resolve this issue will be investigated through computational experiments. Assuming cryogenic superfluid helium, the phase relaxation constant was set to 0.2 meV. Three types of SiV-ND with emission wavelengths were assumed in the calculation: 1.6810 eV, 1.6745 eV, and 1.6720 eV. In the simulation, as shown in Figure 6-1, the excitation laser is irradiated from both sides to cancel out the optical pressure from the excitation light, and then the stimulated emission laser is irradiated from one side. Here, the energy of the stimulated emission laser is set to 1.680 eV. Here, the intensity of the CW laser is 600 W / cm². 2 Figure 6-2 shows the coaxial position of the capillary after irradiating three SiV-NDs with different emission wavelengths with a laser for one hour. In the case of a CW laser, only SiV-NDs with an emission wavelength of 1.6810 eV can be selected. Furthermore, due to the low light intensity, it becomes an absorption force and the NDs are transported in the positive z-axis direction. On the other hand, Figure 6-3 shows the same intensity (average light intensity: 600 W / cm²). 2 This shows the coaxial position of the SiV-ND in the capillary when irradiated with a pulsed laser. However, the repetition rate is 12.5 ns. -1), the pulse width is 500 fs for the excitation light and 200 fs for the stimulated light. In this case, a large light intensity can be generated instantaneously, making it possible to generate stimulated recoil force, which is transported in the negative z-axis direction. Furthermore, in the case of pulsed lasers, if the time bandwidth product is considered, stimulated emission can be induced even for NDs that cannot be stimulated by CW lasers. The SiV-ND migration distances in Figure 6-2 are 3.53 mm, -0.0501 mm, and -0.0770 mm for emission wavelengths of 1.6810 eV, 1.6745 eV, and 1.6720 eV, respectively. On the other hand, the SiV-ND migration distances in Figure 6-3 are -0.707 mm, -0.672 mm, and -0.453 mm for emission wavelengths of 1.6810 eV, 1.6745 eV, and 1.6720 eV, respectively. Therefore, by using a pulsed laser, we were able to transport SiV-ND, which cannot be transported with a CW laser.

Claims

1. A method for separating or concentrating lattice defect-containing ND particles, comprising irradiating a dispersion containing at least two types of ND particles selected from nanodiamond (ND) particles having at least one type of lattice defect and ND particles without the lattice defect with at least one type of excitation laser light having an energy greater than or equal to the resonance absorption energy of the lattice defect and at least one type of stimulated emission laser light, thereby selectively moving the ND particles having the lattice defect by the absorption optical pressure generated by the absorption of at least one type of excitation laser light and the stimulated recoil force generated by the action of at least one type of stimulated emission laser light, wherein the excitation laser light transitions electrons in the ground state of the ND particles to an excited state, and the stimulated emission laser light transitions electrons in the excited state to the ground state faster than spontaneous emission, thereby generating a stimulated recoil force.

2. A method for separating or concentrating ND particles having a lattice defect according to claim 1, wherein the lattice defect is one selected from the group consisting of NV centers, SiV centers, GeV centers, SnV centers, PbV centers, NiV centers, H3 centers, NE8 centers, and P1 centers.

3. A method for separating or concentrating ND particles having a lattice defect according to claim 1, wherein the lattice defect is one selected from the group consisting of NV centers, SiV centers, GeV centers, and P1 centers.

4. A method for separating or concentrating ND particles having lattice defects according to claim 1, comprising irradiating an excitation laser beam and a stimulated emission laser beam in opposing directions.

5. A method for separating or concentrating ND particles having lattice defects according to claim 1, wherein the dispersion is contained in a container having two capillaries connected, and an excitation laser beam and a stimulated emission laser beam are irradiated oppositely to the connecting portion.

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