Method for producing NV center and method for manufacturing diamond particle

Abstract

To efficiently produce an NV center in a diamond particle.SOLUTION: A method for producing an NV center in a diamond particle includes a step of irradiating suspension 9 of diamond particles 1 with pulse light 6 from a pulse laser 5 while stirring the suspension 9.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for creating NV centers in diamond particles and a method for producing diamond particles having NV centers. [Background technology]

[0002] Diamond has excellent optical, electrical, and thermal properties, making it a promising candidate for applications in optical elements and electronic devices. In particular, nitrogen-vacancy centers (NV centers) present inside diamond have attracted attention in recent years. NV centers consist of pairs of nitrogen impurities and adjacent vacancy defects inside diamond. When an electron is trapped in the vacancy, they exhibit a magnetic property called electron spin. The electron spin in NV centers has a long coherence time even at room temperature, and its spin state can be controlled and detected at room temperature. Therefore, diamonds are expected to be used in quantum computing and as highly sensitive quantum sensors for magnetic and electric fields.

[0003] There are various methods for creating NV centers in diamond. For example, nitrogen is added during the synthesis of diamond by CVD (Chemical Vapor Deposition). Other methods include implanting nitrogen ions into diamond, or irradiating diamond that already contains nitrogen with an electron beam or ion beam. In these ion implantation and electron beam or ion beam irradiation methods, NV centers are created in the diamond by high-temperature annealing after ion implantation or irradiation with an electron beam or ion beam.

[0004] In recent years, there have been reports of creating NV centers in diamond using a femtosecond laser, as disclosed in the following Patent Document 1. The method of creating NV centers in diamond using a femtosecond laser is simple and convenient, and is superior to other methods that use electron beam or ion beam irradiation in that it does not require the problem of emitting X-rays or radiation or high-temperature annealing treatment, and further technological progress is expected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2021-526498 Summary of the Invention [Problem to be solved by the invention]

[0006] As mentioned above, NV centers in diamond have attracted attention because they have stability at room temperature and excellent coherence properties, and can be used for multi-sensing of not only magnetic fields but also electric fields, temperature, pH, etc. In particular, NV centers in nanodiamonds, which are nano-sized diamonds, have excellent spatial resolution and low biotoxicity, making them useful in the life sciences, for example, for local measurements within cells, and are expected to have a wide range of applications in biomeasurements.

[0007] On the other hand, the only targets reported so far for creating NV centers using a femtosecond laser have been diamond substrates. Creating NV centers using a femtosecond laser in nano-sized diamond particles such as nanodiamonds has yet to be achieved. In order to apply quantum sensing technology using NV centers in diamond to the fields of life science and biomeasurement, a method for efficiently creating NV centers in diamond particles using a femtosecond laser is needed.

[0008] An object of the present invention is to efficiently create NV centers in diamond particles. [Means for solving the problem]

[0009] The present invention for solving the above problems includes, for example, the following aspects. (Section 1) A method for creating NV centers in diamond particles, comprising the step of irradiating a suspension of diamond particles with pulsed light from a pulsed laser while stirring the suspension. (Section 2) Item 2. The method according to Item 1, wherein the dispersion medium of the suspension is a substance that absorbs heat generated in the diamond particles by irradiation with the pulsed light. (Section 3) Item 10. The method of claim 1, further comprising a step of pretreating the diamond particles. (Section 4) Item 1. The method according to item 1, wherein the diamond particles are nanodiamond particles and the pulse width of the pulsed laser is on the order of femtoseconds. (Section 5) Item 1. The method according to Item 1, wherein the energy of the pulsed laser is 0.5 mJ or more and the irradiation time is 1 hour or more. (Section 6) Providing diamond particles; Item 1 to 5. A step of creating NV centers in the diamond particles by the method according to any one of items 1 to 5; A method for producing diamond particles having NV centers, comprising: [Effects of the Invention]

[0010] According to the present invention, NV centers can be efficiently created in diamond particles. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram for explaining how NV centers are created in diamond particles by a method for creating NV centers according to one embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing a schematic configuration of a measurement system used to evaluate the fabricated NV centers. [Figure 3] 1 is a graph illustrating the results of a comparison between a sample prepared in Example 1 and a sample in which the presence of NV centers is known. [Figure 4] 1 is a graph showing the results of ESR measurements of samples prepared by irradiating a suspension with a pulse laser at various energies and irradiation times in Example 1. [Figure 5] 1 is a graph showing the results of ESR measurements of samples prepared by irradiating a suspension with a pulse laser at various energies and irradiation times in Example 1. [Figure 6] 1 shows the measurement results of the fluorescence spectrum of the sample prepared in Example 1. [Figure 7] FIG. 1 is a diagram showing the results of comparing the fluorescence intensity before and after irradiation with a femtosecond laser in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same reference numerals will denote the same or similar components, and therefore, redundant descriptions of the same or similar components will be omitted.

[0013] [Creation of NV centers] Fig. 1 is a schematic diagram for explaining how NV centers are created in diamond particles by an NV center creation method according to one embodiment of the present invention. In this embodiment, NV centers are created in diamond particles 1 by an NV center creation apparatus 10 shown in Fig. 1. The NV center creation method according to one embodiment will be described below with reference to Fig. 1.

[0014] <Outline of manufacturing method> A method for creating NV centers according to one embodiment is a method for creating NV centers in diamond particles. The method includes a step of irradiating a suspension 9 of diamond particles 1 with pulsed light 6 from a pulsed laser 5 while stirring the suspension 9. In this embodiment, the diamond particles 1 are nanodiamond particles, and the pulse width of the pulsed laser 5 is on the order of femtoseconds (fs). Preferably, the dispersion medium of the suspension 9 is a substance that absorbs heat generated in the diamond particles 1 upon irradiation with the pulsed light 6. Preferably, the energy of the pulsed laser 5 is 0.5 mJ or more, and the irradiation time is 1 hour or more. In this embodiment, the method further includes a step of pretreating the diamond particles 1. The pretreatment includes a step of subjecting the diamond particles 1 to a gas-phase oxidation treatment and a step of subjecting the diamond particles 1 to a thermal mixed acid treatment. As an optional step, the method can further include a step of subjecting the diamond particles 1 irradiated with the pulsed light 6 while stirring the suspension 9 to a thermal mixed acid treatment.

[0015] The NV center preparation method according to one embodiment can be carried out in an atmospheric pressure environment at room temperature (for example, about 1°C to about 30°C), and does not pose the problem of emitting X-rays or radioactive rays. High-temperature annealing is also not required. Therefore, according to the NV center preparation method according to one embodiment, it is possible to efficiently prepare NV centers in diamond particles.

[0016] <Production procedure> Diamond particle preparation Diamond particles 1, which are used to create NV centers, can be manufactured by various methods. In this embodiment, powdered nanodiamond manufactured by the high pressure and high temperature (HPHT) method is prepared. Illustratively, the prepared diamond particles 1 are nanodiamonds with an average particle size of about 100 nm and a nitrogen concentration of about 70 ppm to about 100 ppm.

[0017] Pretreatment of diamond particles In this embodiment, the prepared diamond particles 1 are subjected to the following two types of pretreatment. First, the diamond particles 1 are subjected to a gas phase oxidation treatment in an atmosphere at about 500°C for about 5 hours. The gas phase oxidation treatment is carried out to remove sp remaining on the diamond surface. 2 The carbon is mainly removed. Next, the diamond particles 1 that have been subjected to the gas-phase oxidation treatment are subjected to a thermal mixed acid treatment. The thermal mixed acid treatment removes metal impurities remaining on the diamond surface and sp impurities that could not be completely removed by the gas-phase oxidation treatment. 2 The primary purpose is to remove carbon. In this embodiment, the hot mixed acid treatment is carried out using a liquid mixture of sulfuric acid and nitric acid in a volume ratio of 3:1, in an environment of 130°C for approximately 72 hours. By carrying out these pretreatments, the surface of the diamond is cleaned and simultaneously substituted with hydrophilic carboxyl groups, allowing the diamond particles 1 to have high dispersibility in the dispersing medium described below.

[0018] Preparation of suspension Pretreated diamond particles 1 are introduced into a dispersion medium and mixed to prepare a suspension 9 of diamond particles 1. In this embodiment, water (H2O) is used as the dispersion medium for the diamond particles 1. Illustratively, the concentration of the suspension 9 is approximately 0.4 mg / mL, and a volume of approximately 2 mL of suspension 9 is stored in the glass cell 2. Illustratively, the glass cell 2 for storing the suspension 9 is a roughly rectangular parallelepiped container with an openable top, with outer dimensions of approximately 12.5 mm x approximately 12.5 mm x approximately 45.0 mm and inner dimensions of approximately 10.0 mm x approximately 10.0 mm x approximately 44.0 mm.

[0019] ·Suspension stirring and laser light irradiation The NV center preparation method according to this embodiment is characterized in that stirring of the suspension 9 and irradiation of the suspension 9 with pulsed light 6 are carried out simultaneously in parallel. That is, in the NV center preparation method according to this embodiment, the suspension 9 of diamond particles 1 is stirred while the suspension 9 is irradiated with pulsed light 6 from a pulsed laser 5. This allows the heat generated in the diamond particles 1 by irradiation with the pulsed light 6 to be efficiently absorbed by the dispersion medium, and NV centers are efficiently prepared in the diamond particles 1. As the heat generated in the diamond particles 1 by irradiation with the pulsed light 6 is absorbed by the dispersion medium of the suspension 9, graphitization of the diamond particles 1 is reduced, and NV centers are efficiently prepared in the diamond particles 1.

[0020] To stir the suspension 9, a stirring bar 3 is placed into the suspension 9 in the glass cell 2. The stirrer 4 is, for example, a magnetic type, and the suspension 9 is stirred by rotating the stirring bar 3 at a predetermined rotation speed. The rotation speed of the stirring bar 3 by the stirrer 4 is preferably a rotation speed that does not cause bubbles to form in the suspension 9. Illustratively, the rotation speed of the stirring bar 3 is about 100 rotations per minute (about 100 rpm).

[0021] Pulsed laser 5 is a femtosecond (10 -15 The pulsed laser 5 outputs pulsed light 6 with a pulse width on the order of 100 fs (approximately 100 fs). In this embodiment, the pulsed laser 5 uses chirped pulse amplification (CPA) to output high-intensity laser light with an extremely short pulse on the order of femtoseconds. Illustratively, the wavelength of the pulsed laser 5 is approximately 800 nm, the pulse width is approximately 100 fs (full width at half maximum) and the repetition rate at which the pulsed laser 5 outputs the pulsed light 6 is approximately 1 kHz. Illustratively, the pulse energy of the pulsed laser 5 is in the range of approximately 0.3 mJ to approximately 0.5 mJ, and the time for which the pulsed laser 5 is irradiated onto the suspension 9 is in the range of approximately 0.5 hours to approximately 1 hour. In this embodiment, the distance L1 over which the pulsed light 6 travels through the suspension 9 in the glass cell 2 is approximately 10 mm.

[0022] The objective lens 7 focuses the pulsed light 6 output from the pulsed laser 5 onto the suspension 9 in the glass cell 2. Preferably, the objective lens 7 focuses the pulsed light 6 output from the pulsed laser 5 onto the latter half of the optical path of the pulsed light 6 passing through the suspension 9 in the glass cell 2. The reason for focusing the pulsed light 6 onto the latter half of the optical path by the objective lens 7 is to allow the pulsed light 6 to enter the glass cell 2 while it has a relatively large diameter, so that the pulsed light 6 reacts strongly with the suspension 9 before it leaves the glass cell 2 (i.e., to increase the fluence, which is the energy per unit area). For example, when the distance L1 over which the pulsed light 6 passes through the suspension 9 in the glass cell 2 is approximately 10 mm, the objective lens 7 focuses the pulsed light 6 at a distance of approximately 7.5 mm (denoted by symbol L2) from the upstream side of the optical path. For example, the focal length of the objective lens 7 is approximately 50 mm, and the numerical aperture NA is approximately 0.1. The beam diameter of the pulsed light 6 downstream of the objective lens 7 in the optical path is approximately 10 mm immediately after the objective lens 7 and approximately 2 mm at the surface 2 a of the glass cell 2 .

[0023] Post-treatment of diamond particles After stirring the suspension 9 and irradiating the suspension 9 with the pulsed light 6 simultaneously, as an optional step, the diamond particles 1 can be removed from the suspension 9 and subjected to an additional thermal mixed acid treatment on the diamond particles 1. For example, the additional thermal mixed acid treatment applied to the diamond particles 1 as a post-treatment can be performed under the same process conditions as the thermal mixed acid treatment applied to the diamond particles 1 as a pre-treatment.

[0024] As described above, according to the NV center preparation method of one embodiment of the present invention, NV centers can be efficiently prepared in diamond particles. According to this method, while stirring a suspension 9 of diamond particles 1, pulsed light 6 from a pulsed laser 5 is irradiated onto the suspension 9. NV centers are prepared by irradiating the suspension 9 with the pulsed laser 5, thereby enabling the preparation of NV centers without emitting X-rays or other radiation. The diamond particles 1 are dispersed within the suspension 9, thereby reducing graphitization of the diamond particles 1. High-temperature annealing is also not required. Therefore, according to the NV center preparation method of one embodiment, graphitization of the diamond particles 1 can be reduced while overcoming the problem of emitting X-rays or other radiation, thereby enabling the efficient preparation of NV centers in the diamond particles.

[0025] [Measurement system used for evaluation] The fabricated NV centers can be evaluated by electron spin resonance (ESR) measurements and by measuring fluorescence intensity and fluorescence spectrum. For ESR measurements, a commercially available ESR measurement device can be used. Figure 2 shows a schematic diagram of the measurement system used for fluorescence measurements.

[0026] The produced NV center can be evaluated using, for example, a measurement system 20 shown in Fig. 2. Illustratively, the measurement system 20 can be configured using a known confocal fluorescence microscope.

[0027] For evaluation using the measurement system 20, a sample 19 containing NV centers is prepared. The sample 19 is prepared by dropping a suspension 9 irradiated with pulsed light 6 from a pulsed laser 5 onto a glass slide and then air-drying the suspension 9 using the NV center preparation method according to the embodiment described above, repeatedly. The excitation light 22 (output: approximately 100 μW) output from the excitation light source 21 is laser light with a wavelength of 532 nm (green) and is used to transition NV centers from the ground state to an excited state. The excitation light 22 is reflected by a dichroic mirror 23, focused by an objective lens 24A (numerical aperture NA: approximately 1.45), and applied to the sample 19. If NV centers are present in the sample 19, the NV centers transition from the ground state to an excited state and then relax to the ground state. During relaxation to the ground state, red fluorescence 25 with a wavelength of approximately 700 nm is emitted. The emitted fluorescence 25 is sent to a detector 27 through an optical system 26, and the intensity of the fluorescence 25 is measured by the detector 27. A photodiode for confocal image measurement or a spectrometer for fluorescence spectrum measurement can be used as the detector 27. In the illustrated embodiment, the optical system 26 includes focusing lenses 26A, 26C, and 26D and a pinhole 26B (hole diameter: approximately 30 μm).

[0028] A confocal image of the sample 19 can be acquired by a detector 27. If the sample 19 contains NV centers, the emission intensity of the confocal image will increase due to fluorescence 25 emitted from the sample 19. The position of the objective lens 24A is adjusted by a three-axis piezo stage 24B, allowing excitation light 22 to be focused and irradiated at different positions on the sample 19.

[0029] The following examples of the present invention will be presented to clarify the features of the present invention. Unless otherwise specified, the fabrication conditions, such as the laser wavelength, pulse width, repetition frequency, energy, and irradiation time, are the same in each example. [Example]

[0030] In Example 1, NV centers were created in nanodiamond particles according to the NV center creation method described in the above-mentioned embodiment. Powdered nanodiamond particles manufactured by a high-temperature, high-pressure method were prepared, and the prepared nanodiamond particles were subjected to two types of pretreatment. The pretreated nanodiamond particles were added to a dispersion medium and mixed to create a suspension of nanodiamond particles. Water (H2O) was used as the dispersion medium. While stirring the suspension of the created nanodiamond particles, pulsed light from a femtosecond laser was irradiated onto the suspension. The settings related to the femtosecond laser were the same as those in the above-mentioned embodiment.

[0031] The suspension was irradiated with pulsed light in three cases: Case 1 (no pulsed light irradiation), Case 2 (pulsed light irradiation), and Case 3 (pulsed light irradiation followed by an additional hot mixed acid treatment). Two types of samples were prepared for each of the suspensions in Cases 1 to 3, depending on the two types of measurements to be evaluated. Samples for the first measurement (ESR measurement) were prepared by freeze-drying the suspension and then powdering it. Samples for the second measurement (fluorescence measurement) were prepared by dropping the suspension (1 mg / mL, 5 μL) onto a glass slide and then air-drying it, repeating this process seven times. The following two types of measurements were performed on the prepared samples to verify whether NV centers were formed in the nanodiamond particles in the samples.

[0032] In the first measurement, the prepared sample was measured by electron spin resonance (ESR). The powdered sample prepared for the first measurement was placed in an ESR sample tube made of synthetic quartz. This sample tube was then placed in the cavity of a commercially available high-sensitivity ESR instrument (X-band, 9-10 GHz). Lock-in detection was performed while sweeping the magnetic field near the magnetic field strength at which a known NV center resonance signal was obtained using the ESR instrument, to confirm whether a NV center signal could be obtained from the sample. The ESR measurement results are shown in Figures 3 to 5. In the graphs shown in Figures 3 to 5, the vertical axis represents the signal intensity normalized per unit mass.

[0033] FIG. 3 is a graph illustrating the results of a comparison between the sample prepared in Example 1 and a sample for which the presence of NV centers is known. Measurement results 31, 32, and 33 for the sample prepared in Example 1 are shown in the upper graph, and measurement result 30 for the sample for which the presence of NV centers is known is shown in the lower graph. In the upper graph of FIG. 3, the graph indicated by reference numeral 31 is the measurement result for the sample of the first case, the graph indicated by reference numeral 32 is the measurement result for the sample of the second case, and the graph indicated by reference numeral 33 is the measurement result for the sample of the third case. The energy of the femtosecond laser was approximately 0.5 mJ, and the irradiation time for the suspension was approximately 1 hour.

[0034] As shown in graph 31, it was confirmed that a small number of NV centers existed even in samples that were not irradiated with pulsed light. As shown in graphs 32 and 33, signal peaks were confirmed when the suspension was irradiated with pulsed light while being stirred. Comparing this with graph 30, the signal peak positions of graphs 32 and 33 corresponded to the signal peak position of graph 30. From this, it was inferred that a larger number of NV centers were created in the samples of the second and third cases than in the sample of the first case, which was not irradiated with pulsed light.

[0035] Comparing graphs 32 and 33 confirmed that the signal shapes were roughly the same before and after the thermal acid mixing treatment. Graphs 32 and 33 also showed wider signal linewidths than graph 30. This suggests that the impact of femtosecond laser irradiation is stronger inside the nanodiamond particles than on their surfaces. Comparing graphs 32 and 33 confirmed that the signal peak intensity increased when the thermal acid mixing treatment was performed after pulsed light irradiation. Since the thermal acid mixing treatment itself has not been reported to have the ability to create NV centers, this increase in signal intensity is interpreted as a result of the reduction of impurities such as graphitized nanodiamond particles by performing the thermal acid mixing treatment again after femtosecond laser irradiation, resulting in a relative increase in the number of nanodiamond particles containing NV centers per unit mass, resulting in an increase in signal intensity.

[0036] 4 and 5 are graphs showing the results of ESR measurements on samples prepared by irradiating the suspension with a pulsed laser at various energies and irradiation times in Example 1. The energy of the femtosecond laser was varied in the range of about 0.3 mJ to about 0.5 mJ, and the time for irradiating the suspension with the femtosecond laser was varied in the range of about 0.5 hours to about 1 hour.

[0037] As shown in Figure 4, a significantly strong signal was measured when the femtosecond laser energy was approximately 0.5 mJ and the irradiation time was approximately 1 hour.

[0038] The dependence of the femtosecond laser pulse energy will be discussed with reference to FIG. 5(A). In FIG. 5(A), the graph indicated by reference numeral 51 shows the measurement results for a sample not irradiated with pulsed light. The graph indicated by reference numeral 52 shows the measurement results for a sample irradiated with a femtosecond laser with an energy of approximately 0.3 mJ. The graph indicated by reference numeral 53 shows the measurement results for a sample irradiated with a femtosecond laser with an energy of approximately 0.4 mJ. The graph indicated by reference numeral 54 shows the measurement results for a sample irradiated with a femtosecond laser with an energy of approximately 0.5 mJ. The femtosecond laser irradiation time was approximately 1 hour in all graphs indicated by reference numerals 52 to 54. As shown in FIG. 5(A), as the pulse energy was gradually increased, the strongest signal was measured when a femtosecond laser with an energy of approximately 0.5 mJ was irradiated. The change in signal intensity at this time was rapid.

[0039] The dependence of the femtosecond laser irradiation time will be discussed with reference to Figure 5(B). In the graph of Figure 5(B), the graph indicated by reference numeral 55 is the measurement result for a sample not irradiated with pulsed light. The graph indicated by reference numeral 56 is the measurement result for a sample irradiated with the femtosecond laser for approximately 0.5 hours, and the graph indicated by reference numeral 57 is the measurement result for a sample irradiated with the femtosecond laser for approximately 1 hour. The femtosecond laser energy was approximately 0.5 mJ in both graphs indicated by reference numerals 56 and 57. As shown in Figure 5(B), the irradiation time was gradually increased, and the strongest signal was measured when the femtosecond laser was irradiated for approximately 1 hour. The change in signal intensity at this time was rapid.

[0040] In the second measurement, the fluorescence intensity of the prepared sample was measured. The measurement results of the fluorescence intensity are shown in Figures 6 and 7.

[0041] Fluorescence intensity was measured using the measurement system shown in Figure 2. Confocal images were taken at multiple locations (9 locations in this example) on the sample. For each confocal image, the average pixel value of the luminescence intensity within the image was calculated, and the calculated pixel average values ​​for the multiple imaging locations were added together to calculate the average luminescence intensity per imaging location.

[0042] FIG. 6 shows the measurement results of the fluorescence spectrum for the sample prepared in Example 1. FIG. 6(A) is the fluorescence spectrum obtained by averaging five locations with weak emission intensity among multiple imaging locations on the sample, FIG. 6(B) is the fluorescence spectrum obtained by averaging five locations with high emission intensity among multiple imaging locations on the sample, and FIG. 6(C) is the fluorescence spectrum obtained by averaging ten imaging locations on the sample. FIG. 6(D) is a fluorescence spectrum shown for comparison, showing the NV center (NV - 6 shows the results of measuring the fluorescence spectrum of a bulk diamond substrate for which the presence of NV centers is known. As shown in Figure 6, it was confirmed that the fluorescence spectrum of the sample prepared in Example 1 closely matches the fluorescence spectrum of a substrate for which the presence of NV centers is known, regardless of the intensity of the emission light.

[0043] Figure 7 shows the results of comparing the fluorescence intensity before and after irradiation with a femtosecond laser in Example 1. Figure 7(A) shows the state before the sample was irradiated with a femtosecond laser, and Figure 7(B) shows the state after the sample was irradiated with a femtosecond laser.

[0044] (A1) is a photograph of the entire sample, and (A2) is a confocal image of a certain imaging point 71 on the sample. As shown in (A2), almost no bright spots were observed in the image before the sample was irradiated with the femtosecond laser. The average luminescence intensity in the confocal image shown in (A2) was approximately 130 kcps.

[0045] (B1) is a photograph of the entire sample, and (B2) is a confocal image of a certain imaging point 71 on the sample. As shown in (B2), after irradiating the sample with a femtosecond laser, many bright spots were observed in the image. The average luminescence intensity in the confocal image shown in (B2) was approximately 2600 kcps.

[0046] The average luminescence intensity in the confocal images (A2) and (B2) was compared, and it was confirmed that the average luminescence intensity in the image (B2) was approximately 20 times that in the image (A2).

[0047] [Other forms] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0048] In the above-described embodiment, the size of the diamond particles 1 is nano-sized, but as long as NV centers can be created, the size of the diamond particles 1 is not limited to nano-sized. The size of the diamond particles 1 may be micro-sized, with an average particle size of, for example, about 1 μm.

[0049] In the above-described embodiment, the pulse width of the pulsed light 6 output from the pulsed laser 5 is on the order of femtoseconds (fs), but the pulse width of the pulsed light 6 irradiated onto the diamond particles 1 in the suspension 9 is not limited to the order of femtoseconds. As long as NV centers can be created in the diamond particles 1, the pulse width may be on the order of femtoseconds (fs). -15 seconds), e.g., attoseconds (10 -18 The diamond particles 1 in the suspension 9 may be irradiated with pulsed light 6 having a pulse width on the order of 1000 s (seconds). [Explanation of symbols]

[0050] 1 diamond particles 2. Glass cell 3 Stirrer bar 4. Stirrer 5. Pulsed laser 6 Pulsed Light 7 Objective Lens 9. Suspension 10. NV center production device 19 Samples 20 Measurement System 21 Excitation light source 22 Excitation light 23 Dichroic mirror 24A objective lens 24B Piezo Stage 25 Fluorescence 26 Optical system (lens, pinhole) 27 Detector

Claims

1. A method for producing NV centers in diamond particles, comprising the step of irradiating a suspension of diamond particles with pulsed light from a pulsed laser while stirring the suspension.

2. The method according to claim 1 , wherein the dispersion medium of the suspension is a substance that absorbs heat generated in the diamond particles by irradiation with the pulsed light.

3. The method of claim 1 further comprising the step of pre-treating the diamond particles.

4. The method of claim 1, wherein the diamond particles are nanodiamond particles and the pulse width of the pulsed laser is on the order of femtoseconds.

5. The method of claim 1, wherein the energy of the pulsed laser is 0.5 mJ or more and the irradiation time is 1 hour or more.

6. Providing diamond particles; Creating NV centres in the diamond particles by a method according to any one of claims 1 to 5; A method for producing diamond particles having NV centers, comprising:

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