Luminescent diamond and method for producing same

Abstract

Luminescent diamond is produced by subjecting a volume of diamond abrasive grains and catalytic material to high pressure / high temperature (HPHT) conditions. The pressure device and / or pressure cell are specially configured to apply differential or asymmetric pressure to the diamond volume during HPHT conditions. This subjects the diamond abrasive grains to differential strain, which increases the degree of plastic deformation of the diamond grains and increases the formation of nitrogen vacancy centers. Diamond pellets formed by such a process and subjected to differential pressure can have an aspect ratio or aspect ratio change greater than 1. The temperature of the HPHT process, at or below 1,800°C, promotes the desired nitrogen mobility and preferentially promotes the formation of NV centers over NVN and N3 centers within the diamond pellets, resulting in greater luminescence in the red wavelength spectrum than diamond pellets formed by any other HPHT process.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of and priority to U.S. Patent Application No. 63 / 287,341, filed December 8, 2021, and U.S. Patent Application No. 63 / 374,035, filed August 31, 2022, which are incorporated herein by reference in their entireties. [Background technology]

[0002] Laser injection fluorescence is a known technique employed to better understand how biological systems function at the cellular, subcellular, or molecular level through individually probing tissues, cells, and biomolecules for observation. In one example, laser injection fluorescence can be applied to image and track single molecules or particles in living cells, etc., such as in vivo biosensors for organ mapping, cell imaging, etc. One type of material used in laser injection fluorescence is luminescent nanodiamonds, which are nano-sized diamond particles or abrasives that are developed to emit light when excited by a light source within the desired wavelength required for the end application. Summary of the Invention

[0003] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0004] The luminescent diamond disclosed herein may be made by placing a volume of precursor diamond abrasive grains and catalytic material in a pressure cell, and subjecting the pressure cell to high pressure / high temperature (HPHT) conditions.In one example, the pressure device is specially configured to apply differential pressure or asymmetric pressure on the diamond volume during HPHT conditions, so that when the diamond abrasive grain undergoes differential strain, the differential strain acts to increase the plastic deformation of the diamond abrasive grain, thereby increasing the formation of nitrogen vacancy centers.In one example, the pressure cell is specially configured to apply differential pressure or asymmetric pressure on the diamond volume during HHT conditions, so that when the diamond abrasive grain undergoes differential strain, the differential strain acts to increase the plastic deformation of the diamond abrasive grain, thereby increasing the formation of nitrogen vacancy centers.

[0005] In one example, diamond pellets formed by such a process and subjected to a pressure differential have been shown to have an aspect ratio or undergo a change in aspect ratio greater than 1. In one example, it has been shown that when a cell or pressure device is configured to apply a pressure force in the axial direction that is greater than the radial direction, the diamond abrasive grains experience a negative strain in the axial direction and a positive strain in the radial direction, and the resulting diamond pellets and / or pressed diamond material experience a change in aspect ratio greater than 1 when measured between the axial and radial directions.

[0006] In one example, during the receiving step, the temperature of the HPHT process is about 1,800°C or less to promote the desired nitrogen migration and preferentially promote the formation of nitrogen vacancy (NV) centers in the diamond pellets. In one example, the diamond volume may have an optimized diamond content of about 75-80 wt%, based on the total weight of the diamond abrasive grains and the catalyst material. In one example, the diamond volume may have an optimized diamond content of about 70-100 wt%, 80-95 wt%, greater than 80 wt%, and in certain examples, about 85 wt%. In one example, the catalyst material is a non-metallic solvent catalyst, such as sodium carbonate. In one example, the resulting diamond pellets have a majority of NV centers when compared to bonded dinitrogen vacancy (NVN) centers and when compared to vacancy centers surrounded by three nitrogen atoms (N3). With a majority of the NV population, the resulting diamond pellets have greater emission in the red wavelength spectrum than diamond pellets formed by conventional HPHT processes, i.e., where the diamond grains are subjected to uniform or symmetric pressure, which pressure does not impose differential strains, does not promote increased plastic deformation, and does not promote the formation of nitrogen vacancy centers.

[0007] In one example, the luminescent diamond disclosed herein formed by HPHT processing may be reduced in size to nano-sized luminescent diamond particles useful for forming an aqueous suspension of nano-sized luminescent diamond particles. In one example, the luminescent diamond used to form such a suspension may have an increased diamond content as disclosed above, such as about 70-100 wt%, 80-95 wt%, greater than 80 wt%, and in certain examples, about 85 wt%. In one example, the nano-sized luminescent diamond particles may have an average particle size of about 100 nanometers. In one example, the nano-sized particles may be washed and heat treated prior to forming the aqueous suspension. In one example, the nano-sized diamond particles may be heat treated at a temperature of about 400-550°C. In one example, the aqueous suspension may have a nano-sized luminescent diamond particle content of about 0.1 wt%, based on the total weight of the suspension. In one example, the suspension may have an optical emission intensity of greater than about 10,000 arbitrary units (au) and greater than about 12,000 au in the green wavelength spectrum under the excitation of a 473 nanometer laser, depending on the diamond wt% content.

[0008] These and other features and aspects of the luminescent nanodiamonds and methods for making same disclosed herein will be understood as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1-1] FIG. 1 is a schematic cross-sectional side view of a standard cell structure used for subjecting diamond abrasive grains to high pressure / high temperature processing conditions according to some embodiments of the present disclosure.

[0010] [Figure 1-2]FIG. 1-3 is a schematic cross-sectional side view showing the deformation of diamond abrasive grains using the standard cell structure of FIG. 1-1 and the resulting formation of diamond pellets according to some embodiments of the present disclosure, the resulting diamond pellets being shown to be not subjected to differential strain and to have an aspect ratio of about 1.

[0011] [Figure 2-1] FIG. 2 is a schematic cross-sectional close-up of a conventional mixture of diamond abrasive grains and catalytic material prior to high pressure / high temperature treatment according to some embodiments of the present disclosure, showing the presence of nitrogen atoms therein.

[0012] [Figure 2-2] FIG. 2-2 is a schematic cross-sectional close-up of the mixture of FIG. 2-1 during a first stage of a conventional high pressure / high temperature process that causes deformation and associated nitrogen vacancy centers when subjected to equal, uniform, or symmetric pressure forces, according to some embodiments of the present disclosure.

[0013] [Figure 2-3] FIG. 2-2 is a schematic cross-sectional close-up of the mixture of FIG. 2-1 during a second stage of a conventional high pressure / high temperature process at a temperature below 1800° C. illustrating nitrogen diffusion to form NV centers, according to some embodiments of the present disclosure.

[0014] [Figure 2-4] FIG. 2-2 is a schematic cross-sectional close-up of the mixture of FIG. 2-1 during the second stage of a conventional high pressure / high temperature process at temperatures between 1800-2300° C. illustrating nitrogen diffusion to form NVN centers, according to some embodiments of the present disclosure.

[0015] [Figure 2-5] FIG. 2-2 is a schematic cross-sectional close-up view of the mixture of FIG. 2-1 during the second stage of a conventional high pressure / high temperature process at a temperature above 2300° C. illustrating nitrogen diffusion to form N centers, according to some embodiments of the present disclosure.

[0016] [Figure 3-1]FIG. 2 is a schematic cross-sectional close-up of a mixture of diamond abrasive grains and catalytic material as disclosed herein prior to high pressure / high temperature treatment, showing the presence of nitrogen atoms therein, in accordance with some embodiments of the present disclosure.

[0017] [Figure 3-2] FIG. 3-2 is a schematic cross-sectional close-up of the mixture of FIG. 3-1 during a first stage of the high pressure / high temperature process disclosed herein, which, when subjected to a differential or asymmetric pressure force as disclosed herein, causes deformation, differential strain, and associated formation of nitrogen vacancy centers, according to some embodiments of the present disclosure.

[0018] [Figure 3-3] FIG. 3-2 is a schematic cross-sectional close-up of the mixture of FIG. 3-1 during the high pressure / high temperature second stage disclosed herein at a temperature below 1800° C. to limit nitrogen diffusion to form primarily NV centers, according to some embodiments of the present disclosure.

[0019] [Figure 4-1] FIG. 1 is a schematic cross-sectional side view of an exemplary cell structure disclosed herein configured to promote differential strain in the formed diamond pellets by increasing the degree of diamond abrasive grain deformation in the radial direction during high pressure / high temperature processing conditions according to some embodiments of the present disclosure.

[0020] [Figure 4-2] FIG. 4-2 is a schematic cross-sectional side view showing the deformation of diamond abrasive grains using the exemplary cell structure of FIG. 4-1 and the resulting formation of diamond pellets according to some embodiments of the present disclosure, the resulting diamond pellets being shown to be subjected to differential strain and having an aspect ratio greater than 1.

[0021] [Figure 5-1]FIG. 1 is a schematic cross-sectional side view of an exemplary cell structure disclosed herein configured to promote the formation of diamond pellets undergoing differential strain by providing greater radial diamond grain deformation during high pressure / high temperature processing conditions according to some embodiments of the present disclosure.

[0022] [Figure 5-2] FIG. 5-2 is a schematic cross-sectional side view showing the deformation of diamond abrasive grains using the exemplary cell structure of FIG. 5-1 and the resulting formation of diamond pellets according to some embodiments of the present disclosure, the resulting diamond pellets being shown to be subjected to differential strain and having an aspect ratio greater than 1.

[0023] [Figure 6-1] FIG. 1 is a schematic cross-sectional side view of a standard cell structure used by a standard pressure device to apply equal, uniform, or symmetrical axial and radial pressures to the cell structure to subject diamond abrasive grains within the cell structure to high pressure / high temperature processing conditions according to some embodiments of the present disclosure.

[0024] [Figure 6-2] FIG. 6-1 is a schematic cross-sectional side view showing the deformation of diamond abrasive grains using the standard pressure apparatus and standard cell structure of FIG. 6-1 and the resulting formation of diamond pellets according to some embodiments of the present disclosure, the resulting diamond pellets being shown to be not subjected to differential strain and to have an aspect ratio of about 1.

[0025] [Figure 7-1] FIG. 1 is a schematic cross-sectional side view of a standard cell structure used by an exemplary pressure device disclosed herein, configured to apply differential pressure to the cell in the axial and radial directions to promote differential strain formation of diamond pellets due to greater radial diamond grain deformation during high pressure / high temperature processing conditions, according to some embodiments of the present disclosure.

[0026] [Figure 7-2] FIG. 7-2 is a schematic cross-sectional side view showing the deformation of diamond abrasive grains using the exemplary pressure apparatus of FIG. 7-1 and the resulting formation of diamond pellets, which are shown to be subjected to differential strain and have an aspect ratio greater than 1, in accordance with some embodiments of the present disclosure.

[0027] [Figure 8] 1 is a graph showing the light emission intensity of photoluminescent diamond as a function of diamond content according to some embodiments of the present disclosure.

[0028] [Figure 9] 5A-5C are photographs of luminescent diamond pellets sintered at the same temperature and having different diamond content, according to some embodiments of the present disclosure.

[0029] [Figure 10-1] 4 is a graph showing optical emission intensity versus wavelength for a material with 85% diamond content that was then heat treated at 515° C.

[0030] [Figure 10-2] 1 is a graph showing the emission intensity of luminescent diamond as a function of diamond content according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Some embodiments of the present disclosure relate to luminescent diamond, which may also be referred to as photoluminescent diamond. In some additional embodiments, methods and devices useful for producing luminescent diamond are described, including producing diamond pellets with enhanced plastic deformation and increased amount of nitrogen vacancy center (NV, NVN, or N3). The increase in nitrogen vacancy center can increase the luminescence in one or more spectra. For example, the increase in luminescence can occur in the red wavelength spectrum.

[0032] In some embodiments, the luminescent diamonds (e.g., photoluminescent diamonds) and methods of making them disclosed herein are designed in a way that increases production efficiency and production volume, thereby improving the availability and usability of the material in end uses, including but not limited to biological applications. Luminescent diamonds, in such embodiments, can be produced with less cost, energy, time, or any combination thereof, potentially increasing the usability of such luminescent diamonds.

[0033] Furthermore, in some embodiments, luminescent diamond prepared according to the principles disclosed herein exhibits similar or higher levels of luminescence intensity than conventional luminescent diamond, thereby presenting an opportunity to expand the range of potential end-use applications of such materials. For clarity, in some embodiments, the luminescent diamond of some embodiments herein is first formed by compaction deformation and consolidation of existing diamond abrasive grains to form a luminescent active sintered body or slug (characterized by a high degree of intercrystalline diamond bonding) or to form a mechanically bonded semi-sintered body or slug (characterized by a low degree or substantially no intercrystalline diamond bonding). In such conditions, the compacted material is referred to herein as luminescent diamond. During subsequent processing, the luminescent diamond can be heat treated and / or reduced to a size required by a particular end-use application, and in some embodiments, the resulting diamond grain or abrasive grain can be nanoscale in size. In some examples, the reduced size luminescent diamond may be only nano-sized grains or may include a combination of nano-sized grains and coarser diamond grains. The term "nanodiamond" as used herein is understood to refer to luminescent diamond, including nano-sized diamond particles, for example having an average size of up to 1000 nm (e.g., between 1 nm and 1000 nm).

[0034] In some embodiments, the luminescent diamond disclosed herein may be formed by combining a volume of precursor diamond abrasive grains, which may be in the form of natural and / or synthetic diamond abrasive grains, and placing the volume of diamond abrasive grains in a cell, can, or container that is conventionally used for compaction transformation of diamond abrasive grains. In one example, the diamond abrasive grains may have an average particle size of 1 μm to 1000 μm, 1 μm to 100 μm, or 10 μm to 50 μm. In other embodiments, the size of the initial diamond abrasive grains or powders may extend into the submicron or nano diamond range, as described herein. In some embodiments, nano-sized powders formed by either mechanical crushing of conventional diamond powders or detonation processes may be used in a similar manner. Conventional diamond powders can be either synthetic or natural, but in some cases, synthetic diamond powders have a higher intrinsic nitrogen content that makes the diamond luminescence active with adjacent vacancy centers. In one example, the starting diamond material has an intrinsic amount of nitrogen impurity consistent with that found in diamond designated as Type 1b (e.g., 50 ppm or more nitrogen). Nanopowders synthesized by shock synthesis can also have a high intrinsic nitrogen content.

[0035] In an exemplary embodiment, the cell, can, or container (cell or pressure cell, respectively) is specially configured to apply differential or asymmetric pressure, e.g., axial pressure different from radial pressure, to its contents when undergoing a high pressure / high temperature (HPHT) compaction deformation process using conventional press equipment to make polycrystalline diamond. As described in more detail herein, the differential pressure applied by the cell disclosed herein can increase the degree of plastic deformation, resulting in a higher number of nitrogen vacancy centers, which are useful for increasing the amount of NV centers formed in the resulting luminescent diamond pellet, and correspondingly increase the amount of light emission in the red wavelength spectrum. In an exemplary embodiment, the press equipment or device used to apply pressure to the cell, can, or container may be specially configured to apply differential or asymmetric pressure (e.g., axial pressure different from radial pressure) to the cell and the contents therein when undergoing a HPHT compaction deformation process using such specially configured press equipment to make polycrystalline diamond. As described in more detail herein, the differential pressure applied by the pressing apparatus disclosed herein can result in a greater degree of plastic deformation, resulting in a greater number of nitrogen vacancy centers available to increase the amount of NV centers formed in the resulting luminescent diamond pellet, thereby increasing the amount of light emitted (in the red wavelength spectrum).

[0036] In another exemplary embodiment, the pressure difference is at least 5%. For example, the axial pressure applied by the press instrument or by the pressure cell may be at least 5%, 10%, 15%, 25%, 50%, 100%, or 200% (or any value therebetween) greater than the radial pressure applied by the press instrument or by the pressure cell. In other embodiments, the radial pressure applied by the press instrument or by the pressure cell may be at least 5%, 10%, 15%, 25%, 50%, 100%, or 200% (or any value therebetween) greater than the axial pressure applied by the press instrument or by the pressure cell.

[0037] In an exemplary embodiment, a volume of diamond abrasive grains is placed in a cell, can, or container, which may or may not be sealed, and placed in a HPHT press and subjected to the desired sintering pressure and temperature conditions. In some embodiments, the HPHT process temperature may be in the range of 1300-2500°C, and the process pressure may be about 3.0 GPa to about 10 GPa. In examples where it is desirable to increase the amount of NV centers formed in the luminescent diamond during the HPHT process, it may be desirable to limit the rate of nitrogen diffusion and control nitrogen migration to vacancy sites by controlling the HPHT process temperature to about 1800°C or less (e.g., in the range of 1500°C to 1800°C, in the range of 1350°C to 1600°C), and in some cases below 1500°C (e.g., 1300°C to 1500°C). With less nitrogen migration, NV centers can be preferentially created over other nitrogen vacancy centers (e.g., NVN or N3 centers) that may have more nitrogen atoms available.

[0038] NV centers luminesce in the red wavelength spectrum. In particular, in the red wavelength spectrum, the luminescence may have a wavelength between 620 nm and 700 nm, between 630 nm and 700 nm, and / or a peak centered between 650 nm and 680 nm (e.g., 660 nm or 675 nm). In some embodiments, NV centers can be preferentially generated over other nitrogen vacancy centers. For example, NV centers can be preferentially generated over NVN centers that luminesce in the green wavelength spectrum (e.g., having a wavelength between 495 nm and 570 nm, with a peak centered at 525 nm). To preferentially create NV centers, or even to create mainly or only NV centers, nitrogen diffusion can be somewhat suppressed, since the aforementioned nitrogen concentration (e.g., >50 ppm) can always be higher than the NV concentration (e.g., between 1 ppm and 3 ppm in some commercial materials). In some embodiments and methods, suppression of nitrogen diffusion may be required to preferentially or predominantly generate NV centers.

[0039] In one example, the diamond grain volume may be substantially free of catalytic material, so that the diamond material resulting from the HPHT process is not fully sintered, but rather in the form of a semi-sintered slug or semi-sintered body that includes diamond grains mechanically bonded together by frictional contact, cold welding, diamond self-diffusion, etc. In one example, the diamond grain volume may include some amount of catalytic material, and the type of catalytic material may vary (e.g., the catalytic material may be a metal solvent catalyst as described herein or a non-metal solvent catalyst). In one example, the diamond grains are combined with a non-metal solvent material. In some embodiments, the feature of producing a diamond material that is not fully sintered (i.e., semi-sintered and not characterized by a network of diamond grains bonded together using a conventional metal solvent catalyst) may increase its transparency relative to that of a polycrystalline diamond fully sintered body, which may improve the intensity of the light emitted therefrom. There may also be graphite formed within the porous regions of the semi-sintered body, which may reduce the intensity of the light emitted. In such cases, it may be desirable to partially or completely remove the graphite material as part of the manufacturing process.

[0040] It has been found that during HPHT process, at least a part of the volume of precursor diamond grain can undergo plastic deformation.In some embodiments, the degree of HPHT compaction deformation process is such that it causes sufficient plastic deformation and nitrogen diffusion in diamond grain to create nitrogen vacancy centers (e.g., containing one or both of nitrogen vacancy (NV) or dinitrogen vacancy (NVN) centers) and / or creates optical centers in which three nitrogen atoms surround a vacancy (N3) center in diamond grain, which act to activate the luminescence of diamond grain.The results of the inventors' tests show that the plastic deformation of diamond grain during HPHT creates vacancy centers when deformation mechanisms such as crystal dislocation motion become active, and these vacancies are then known to combine with nitrogen impurities to form vacancy centers containing one or more of NV centers, NVN centers, or N3 optical centers, which cause desired luminescence activity. In some embodiments, this occurs during conventional sintering of polycrystalline diamond with metal catalysts (e.g., cobalt, which acts to promote intercrystalline diamond bonding during the HPHT process) or non-metal catalysts / pressure transfer media (e.g., carbonates and chlorides, which do not promote intercrystalline diamond bonding during the HPHT process). In other embodiments, the diamond abrasive grains obtained from the HPHT process can be plastically deformed to intentionally create a greater range of NV and / or NVN centers and / or N3 centers while inducing weaker diamond-diamond bonds compared to solvent-catalyzed bonded polycrystalline diamond. For example, in some embodiments, it is desirable to subject the diamond abrasive grains to plastic deformation during the HPHT process that causes luminescence activity without resulting in a fully sintered body, so that downstream processes such as particle size classification of the diamond abrasive grains by a crushing process are easier and less energy consuming. For example, instead of other and additional actions, it may be necessary to only break and separate the mechanically bonded diamond abrasive grains.

[0041] In some embodiments, the luminescent diamond disclosed herein may be formed in a similar manner by subjecting a volume of diamond precursor abrasive grains to a HPHT process in the presence of a catalytic material. In such embodiments, the type of catalytic material used may be selected from a group including, but not limited to, Co, Fe, Ni, carbonates, or combinations thereof, for the production of polycrystalline diamond (PCD) products. In some embodiments, Si may be added and used to create reaction-bonded silicon carbide PCD products. In some embodiments, HPHT processing conditions for cobalt PCD may be within a temperature of 1300°C to 1500°C and a pressure of 5.0GPa to 7.5GPa. Additionally, cobalt PCD may be heat treated in vacuum at a temperature of 600°C to 700°C. The amount of catalytic material used can and will vary depending on factors such as the type of catalyst used, the amount of light emission desired, and the particular end use. In biological end uses, the presence of metallic materials within the luminescent diamond may be undesirable and / or unacceptable for biocompatibility reasons, in which case it may be desirable to use a non-metallic catalyst. In some embodiments, the use of non-metallic catalysts results in a PCD body that has relatively high transparency or is less opaque than PCDs formed using metal solvent catalysts. In some embodiments, non-metallic catalysts useful for making luminescent diamonds disclosed herein include carbonate catalysts such as magnesium carbonate, sodium carbonate, calcium carbonate, etc., which result in the formation of carbonate PCD (CPCD).

[0042] FIG. 1-1 illustrates a conventional or standard cell or container 10 used to form polycrystalline diamond by the HPHT process. In such an example, the cell 10 includes one or more internal chambers 12 configured to accommodate a volume of diamond abrasive grains therein, which may be a mixture of diamond abrasive grains and catalytic material. In such an example, the cell includes axial elements 14, 16, and 18 formed from pressed disks of sodium chloride, cesium chloride, or the like, and radial elements 20 and 22 in the form of rings formed from pressed sodium chloride, cesium chloride, or the like. The exemplary cell 10 is configured to receive an equal, uniform, or symmetrical pressure (equal pressure in the axial and radial directions) applied to the cell by a pressing device, and to transmit and apply the uniform or symmetrical pressure to the volume of diamond abrasive grains in the chamber 12. A cell such as that shown in FIG. 1-1 is useful for forming luminescent diamond during HPHT processing at pressing temperatures between 1800°C and 2300°C, and the resulting luminescent diamond may have some NVN centers (emitting in the green wavelength spectrum) and a smaller number of NV centers (emitting in the red wavelength spectrum), resulting in a relatively low overall emission due to luminescence in the red wavelength spectrum. This relatively low number of NV centers is believed to be due to the relatively high amount of nitrogen present to migrate to and fill the nitrogen centers during the HPHT process, as well as the relatively low amount of plastic deformation that takes place. The high amount of available nitrogen and the low amount of nitrogen vacancies favor the formation of NVN centers in the luminescent diamond produced in such a manner. Below 1800°C, it has been observed that primarily NV centers are formed, but the NV centers may not be formed in a high enough concentration to give emission intensities comparable to commercially available NV nanodiamond materials. This is believed to be due to insufficient plastic deformation of diamond and formation of vacancy centers at temperatures below 1800°C. FIG. 1-2 illustrates diamond abrasive grains 24 that may be configured to apply an even force during the HPHT process using cell 10.As shown, the resulting diamond abrasive grain is uniformly strained and has an aspect ratio measured between its width and height dimensions that is approximately 1.

[0043] Figures 2-1-2-5 show a volume of a conventional mixture of diamond powder catalyst material when subjected to a HPHT process to form diamond pellets as described with respect to Figures 1-1 and 1-2. Figure 2-1 shows a volume 200 of a conventional mixture of diamond powder and catalyst material before undergoing HPHT treatment, showing nitrogen atoms 202 present in the mixture. Figure 2-2 shows a diamond volume 204 after undergoing a first stage of HPHT treatment in which a press device uses a cell to apply equal, equal, or symmetric pressure to the volume, where the diamond volume is subjected to pressure without significantly increasing the temperature. After this initial pressurization, heat can be increased inside the cell to increase the temperature within the volume. Since the HPHT cell is designed to provide uniformity in the applied pressure, any diamond plastic deformation is due to distortion of the randomly oriented diamond crystals in response to the applied heat and pressure. The combination of heat and pressure with the randomly oriented diamond crystals induces plastic deformation in the diamond crystals, thereby creating vacancies 206 in the diamond lattice.

[0044] FIG. 2-3 shows a diamond volume 208 after undergoing a second stage of the described HPHT process with equal axial and radial pressures, where equal, equal or symmetric pressures are maintained and the temperature is increased to a temperature below 1800° C., whereby nitrogen atoms 202 diffuse and migrate into the vacancies 206 to form nitrogen vacancy centers including NV centers 210. FIG. 2-4 shows a diamond volume 212 after undergoing a second stage of the described HPHT process, where equal, equal or symmetric pressures are maintained and the temperature is increased to between 1800° C. and 2300° C., whereby a larger amount of nitrogen atoms 202 (compared to that of FIG. 2-3) diffuse and migrate into the vacancies 206 to form nitrogen vacancy centers including NVN centers 214. FIG. 2-5 shows a diamond volume 216 after undergoing a second stage of the described HPHT process, whereby the same, equal or symmetric pressure is maintained and the temperature is increased to above 2300° C., causing a greater amount of nitrogen atoms 202 (compared to that of FIG. 2-4) to diffuse and migrate into the vacancies 206, thereby forming nitrogen vacancy centers, including N3 centers 218.

[0045] Thus, as shown in Figures 2-1 to 2-5, the diamond volume of conventional diamond powder can contain a relatively large number of nitrogen atoms available for diffusion and migration during the second stage of HPHT processing to form NV, NVN, and N3 centers depending on the specific HPHT temperature conditions. In general, the presence of a relatively large number of nitrogen atoms combined with the HPHT process with the same, equal, or symmetric pressure conditions results in a relatively small amount of nitrogen vacancies being formed (during the first stage of HPHT processing) and a relatively large amount of nitrogen being available for diffusion and migration to combine with vacancies to promote the formation of nitrogen vacancy centers, including NVN or N3 centers, over NV centers. NV centers may be desirable in some applications to provide luminescence in the red wavelength spectrum.

[0046] 3-1 and 3-2 show a volume 220 of a mixture of diamond powder catalyst material disclosed herein when subjected to the HPHT process disclosed herein to form diamond pellets that emit light primarily in the red wavelength spectrum. FIG. 3-1 shows a volume 220 of a mixture of diamond powder and catalyst material disclosed herein before undergoing the HPHT process disclosed herein, the volume 220 including nitrogen atoms 222 present in the mixture, less nitrogen atoms 222 present than the volume of the more conventional diamond powder and catalyst material shown in FIG. 2-1. It may be desirable to have fewer nitrogen atoms present in the volume 220 to promote the formation of NV centers by limiting the amount of nitrogen present to form NVN and N3 centers by reducing the amount of nitrogen present for diffusion and migration during HPHT processing. In some embodiments, low nitrogen content diamond is less than 50 ppm, and optionally less than 25 ppm. To achieve this low concentration, a nitrogen "getter" such as aluminum or titanium powder can be used in the diamond powder synthesis process.

[0047] FIG. 3-2 shows a diamond volume 224 after undergoing a first stage of the HPHT process disclosed herein, where a differential or asymmetric pressure is applied to the volume by a specially configured press device and / or a specially configured cell, and in such a first stage, the diamond volume is subjected to a differential pressure. During the pressing and initial heating of the HPHT process disclosed herein, the diamond volume 224 can undergo an increased degree of plastic deformation (compared to the example shown in FIG. 2-2) that creates a diamond pellet in which the volume is subjected to a differential stress and the number or concentration of vacancies 226 is increased (compared to the example shown in FIG. 2-2). FIG. 3-3 shows a diamond volume 228 after undergoing a second stage of the HPHT process disclosed herein, where a differential or asymmetric pressure is applied / maintained and the temperature is optionally changed. For example, the temperature can be changed or increased to a temperature below 1800° C. (or below 1500° C.) so that the nitrogen atoms 222 can diffuse and migrate to the vacancies 226 and form nitrogen vacancy centers, including NV centers 230. Thus, in some embodiments, when voids 226 are created by a pressure differential, the pressure and / or temperature conditions may not be maintained.

[0048] Thus, as shown in Figures 3-1 to 3-3, by controlling the number of nitrogen atoms in the volume of diamond powder, the amount of nitrogen present for diffusion and migration during the HPHT process can be controlled. The pressure applied to the volume during the HPHT process can also be differential or asymmetric pressure, with the purpose of increasing the degree of plastic deformation and / or differential stress on the volume. Such a difference can result in an increase in the number or concentration of vacancies in the diamond pellet. Also, the temperature can be controlled during the HPHT process to control the number of nitrogen atoms available for diffusion and migration, which can encourage the preferential formation of NV centers over NVN and / or N3 centers, resulting in the formation of diamond pellets that emit predominantly in the red wavelength spectrum.

[0049] FIG. 4-1 shows an exemplary cell 30 according to an embodiment disclosed herein, which is specially configured to receive a uniform force from a HPHT press apparatus and apply a differential or asymmetric pressure to a volume of diamond abrasive grains contained therein to increase the amount of plastic deformation of the diamond abrasive grains and thereby increase the amount of nitrogen vacancy centers formed therein. In one example, the cell 30 is configured to have one or more internal chambers 32 configured to accommodate a volume of diamond abrasive grains or a mixture of diamond abrasive grains and catalytic material therein. The cell 30 can include axial elements 34, 36, and 38 (e.g., formed from a press disk of cesium chloride powder) for transmitting the force of the axial pressure from the press apparatus to the diamond volume in the internal chamber 32. The cell 30 can also include radial elements 40 and 42 (e.g., formed from a material configured not to transmit the full radial pressure of the press apparatus to the volume of diamond abrasive grains). In one example, the radial elements can be formed from loose cesium chloride powder, cesium chloride pressed components that are compacted at a low density, and the like.

[0050] When configured in this manner and subjected to the uniform pressure of the press during the HPHT process, the cell 30 operates to apply a differential or asymmetric pressure to the volume of diamond abrasive grains. In this example, the cell 30 applies a greater pressure in the axial direction (y direction in FIG. 4-1) than in the radial direction (x direction in FIG. 4-1). Although the exemplary cell 30 is configured to apply a greater pressure in the axial direction than in the radial direction, the cells disclosed herein may be configured to apply a greater pressure in the radial direction than in the axial direction, or to apply a differential or asymmetric pressure in other directions, and all such cells configured to apply a differential or asymmetric pressure in different directions to the volume of diamond abrasive grains are understood to be within the scope of the present disclosure.

[0051] FIG. 4-2 shows diamond grain 44 deformed by applying differential force during HPHT process using cell 30. As shown, the resulting diamond grain is subjected to differential strain, with the strain being positive in one direction and negative in another direction. The diamond pellet resulting from such differential strain is shown to have an aspect ratio greater than 1 when measured between the width and height dimensions. With reference to FIG. 4-2, the aspect ratios illustrated in schematic form show the difference between the original (pre-pressed) shape (see, for example, diamond grain 24 in FIG. 101) and the resulting (pressed) shape (see diamond grain 44). It should be understood that the original diamond grain may be generally symmetrical or have an aspect ratio of about 1, but this is not required. Alternatively, the pre-pressed diamond grain may have an aspect ratio less than 1 or greater than 1. As a result, the aspect ratios described may be the aspect ratios observable in the physical structure when subjected to the HPHT process, but may instead be reflected as changes in aspect ratio from the original pre-press shape.

[0052] Thus, in some embodiments, the aspect ratio or change in aspect ratio is between greater than 1 and 2 (e.g., greater than 1.1 and 2, or greater than 1.25 and 1.75).As shown in FIG. 2-2, the pressure differential applied to the diamond grains acts to increase the degree of plastic deformation between the diamond grains, thereby creating a greater number of nitrogen vacancy centers therein, as compared to using a symmetric cell 10 during HPHT processing as discussed with respect to FIG. 1-1.

[0053] In some embodiments, rather than describing the aspect ratio or aspect ratio change with respect to shape with reference to the diamond abrasive grain, the aspect ratio and aspect ratio change can be reflected in the combination of diamond abrasive grains that are pressed. For example, a billet may be formed from the diamond abrasive grains and the billet may be pressed under HPHT conditions as described herein. The billet may then undergo a shape change, and in some embodiments, the aspect ratio change is greater than 1. For example, a billet having a rectangular cross-sectional shape (see FIG. 9) may undergo HPHT processing, and in some embodiments, the aspect ratio change of the billet may be greater than 1.

[0054] Although the cell 30 disclosed herein can be operated to increase the degree of plastic deformation and the resulting nitrogen vacancy centers to encourage the formation of a greater amount of nitrogen vacancy centers in the resulting luminescent diamond (e.g., increased creation of NV centers to encourage red luminescence), the HPHT process can be performed using a controlled temperature (e.g., about 1800°C or less), so that the rate of diffusion of nitrogen for migration to locations adjacent to the vacancies is somewhat controlled. This allows NV centers to be preferentially created over NVN centers and / or N3 centers. Thus, in some embodiments, it is desirable for the HPHT process temperature to be about 1800°C or less (e.g., between 500°C and 1800°C, or between 1200°C and 1800°C), about 1500°C and 1800°C, or less than about 1500°C (e.g., between 500°C and 1500°C, or between 1200°C and 1500°C). In some cases, it may be beneficial to heat treat the material following the HPHT process at a temperature to enhance and potentially maximize the luminescence intensity. For example, the material may be heat treated in a standard vacuum furnace at temperatures up to 1300° C., although other heat treatment methods or temperatures may be used (e.g., above or below 1300° C.).

[0055] FIG. 5-1 shows an exemplary cell 50 according to some embodiments, which is specially configured to receive a uniform force from a HPHT press and apply a pressure differential to a volume of diamond abrasive grains contained therein to increase the amount of plastic deformation of the diamond abrasive grains, thereby increasing the number or concentration of nitrogen vacancy centers formed therein. In one example, the cell 50 is configured to have one or more internal chambers 52 configured to accommodate a volume of diamond abrasive grains or a mixture of diamond abrasive grains and catalytic material therein. The cell 50 includes axial elements 54 and 56 that are axially offset from each other on the top and bottom of the cell, respectively. In some embodiments, the axial elements 54, 56 are formed from a high density material with minimal porosity. The cell 50 of FIG. 5-1 also includes radial elements 55 and 57 that are optionally formed from a low density material with high porosity. In one example, the low density material can be a low density solid such as MgO and / or ZrO2, such as not sintered to true density, including significant porosity, and combinations thereof. Although separate radial elements 55, 57 are shown in some embodiments, radial elements 55, 57 may be a unitary piece formed, for example as a cylinder that extends completely or partially around chamber 52.

[0056] The cell 50 may also include one or more intermediate axial elements 58, 60, and 62. In the illustrated embodiment, the axial element 58 is disposed between the axial element 54 and the top of the first internal chamber 52, the axial element 60 is disposed between the first and second internal chambers 52, and the axial element 62 is disposed between the axial element 56 and the bottom of the second internal chamber 52. In an exemplary embodiment, the intermediate axial elements 58, 60, and 62 are at least partially formed from an incompressible material. In one example, the incompressible material may be a fluid, such as a liquid metal, such as iron, nickel, cobalt, or a combination thereof. These metals may be confined in a refractory metal container to control the position of the material within the cell as melting occurs. The cell may also be constructed using cermets containing these metals, such as WC-Co, WC-Ni, WC-Fe, or the like, or a combination thereof.

[0057] When configured in this manner and subjected to the uniform pressure of the press during the HPHT process, the cell 50 can operate to apply a differential pressure to the volume of diamond abrasive grains. In this example, the cell 50 applies a greater pressure in the axial direction than in the radial direction (due to the presence of the incompressible intermediate axial elements 58, 60, and 62). The pressure difference can cause the diamond abrasive grains to undergo different strains, for example, negative axial and positive radial strains, increasing the degree of plastic deformation of the diamond abrasive grains. Although the exemplary cell 50 is configured to apply a greater pressure in the axial direction than in the radial direction, the cells disclosed herein may be configured to apply a greater pressure in the radial direction than in the axial direction, or to apply a differential or asymmetric pressure in other directions, and it is understood that all such cells configured to apply a differential or asymmetric pressure in different directions to the volume of diamond abrasive grains for the purpose of increasing the plastic deformation of the diamond abrasive grains are within the scope of the present disclosure.

[0058] FIG. 5-2 shows diamond grain 64 deformed by applying differential force during HPHT process to the diamond grain to cause the diamond grain to undergo differential strain. As shown, the resulting diamond grain is shown to have an aspect ratio, measured between width and height dimensions, greater than 1. The differential pressure applied to the diamond grain can act to cause the diamond grain to undergo differential strain, which increases the degree of plastic deformation between the diamond grains, thereby causing a higher number or concentration of nitrogen vacancy centers therein, as compared to using the symmetric pressure of cell 10 of FIG. 1-1 during HPHT processing discussed herein. Cell 50 can also operate to promote the creation of NV centers in luminescent diamond during HPHT process under the same or similar temperature conditions described with reference to cell 30 shown in FIG. 4-1.

[0059] Figure 6-1 shows a cell 70 that may be used with a conventional pressing apparatus configured to apply uniform force (i.e., equal force in axial direction 71 and radial direction 73) on the cell 70 during the HPHT process used to form the luminescent diamond. Thus, the cell 70 may be similar to the cell 10 of Figure 1-1.

[0060] As shown, the pressure applied to the cell 70 by the pressing device is the same in the radial and axial directions, so that the diamond grain undergoes uniform strain, which limits plastic deformation. Figure 6-2 shows diamond grain 72 deformed by applying uniform force during the HPHT process using the standard cell 70. As shown, the resulting diamond grain undergoes uniform strain and is shown to have an aspect ratio measured between the width and height dimensions that is about 1. As described herein, at symmetrical HPHT process pressures and temperatures, luminescent diamonds created by the HPHT process using such a cell 70 and pressing device can create a larger amount of NVN centers than desired, and potentially more NVN centers than NV centers, thereby emitting a quantity of light emission in the red wavelength spectrum, which may not be sufficient or desirable for certain end uses, i.e., those that require a large amount of light emission in the red wavelength spectrum.

[0061] FIG. 7-1 illustrates an exemplary press apparatus 80 configured to apply a differential or asymmetric pressure to cells 82 and containing a volume or mixture of diamond abrasive grains in one or more internal chambers 84 during HPHT processing. In one example, the press apparatus 80 can be of any type capable of applying a differential or asymmetric pressure to cells 82 in an axial direction more than a radial direction. In one example, the press apparatus 80 can be a conventional or proprietary cube press, a solid frame press, a belt press, or the like. In the illustrated example, the press apparatus 80 is configured to apply a differential pressure to cells 82 that is greater in an axial direction 83 than in a radial direction 85, thereby subjecting the diamond abrasive grains to differential strain as described above. It should be understood that the press apparatus disclosed herein may alternatively be configured to apply a pressure to cells 82 that is greater in a radial direction than in an axial direction. It is therefore understood that the pressing devices disclosed herein may be configured to apply greater pressure in the radial direction than in the axial direction, or to apply differential or asymmetric pressure in other directions, and all such pressing devices configured to apply differential or asymmetric pressure to cells in different directions for the purpose of increasing plastic deformation are understood to be within the scope of the present disclosure.

[0062] In one example, the cell 82 may be a standard cell configured to not create a pressure differential between the pressing apparatus and the volume of diamond abrasive grains in the internal chamber 84. Alternatively, the cell may be an exemplary cell disclosed above configured to contribute to the pressure differential applied by the pressing apparatus, e.g., while the pressing apparatus applies a pressure differential, the cell itself may operate to increase the pressure differential applied to the diamond volume. In one example, the pressing apparatus 80 operates during the HPHT process under the same or similar temperature conditions as described herein to promote increased formation of NV centers in the resulting luminescent diamond.

[0063] FIG. 7-2 shows a diamond grain 86 deformed by using a press device 80 and a cell 80, which applies a differential force on the cell during the HPHT process. As shown, the diamond grain undergoes a differential strain that produces a diamond grain that is shown to have an aspect ratio, measured between the width and height dimensions, greater than 1. As shown in FIG. 5-2, the differential pressure is transmitted by the cell and applied onto the diamond grain, which increases the degree of plastic deformation between the diamond grains and creates a higher number or concentration of nitrogen vacancy centers therein, compared to using a standard press device configured to apply an even or symmetric pressure to the cell during HPHT processing as described above.

[0064] Some features of the cells and presses disclosed herein are the ability to apply dynamic or asymmetric pressure to the diamond grain during HPHT treatment. The ability of diamond to plastically deform can also be enhanced by applying higher temperatures. Thus, various structures and components described herein can be used as a means to apply asymmetric pressure to the diamond grain or internal chamber during HPHT treatment. Exemplary means may include cells including structures that apply asymmetric pressure to the internal chamber of the cell using symmetric pressure on the exterior of the cell (e.g., Fig. 4-1 and Fig. 5-1), presses including structures that apply different pressures in different directions (e.g., Fig. 7-1), or combinations thereof. In some embodiments, HTHP treatment at the temperature conditions described herein serves to increase the degree or amount of plastic deformation in the diamond grain, thereby increasing the number or concentration of vacancies relative to a controlled amount of available nitrogen (by the controlled temperature of the HPHT process), forming NV centers at a concentration that is opposite or exceeds the concentration of NVN centers. Thus, luminescent diamond formed in this manner may emit more light in the red wavelength spectrum than luminescent diamond formed using HPHT processing cells and / or pressing apparatus under more conventional diamond sintering HPHT temperatures or other processes that produce a more significant number or concentration of NVN centers.

[0065] In an exemplary embodiment, the diamond abrasive grains are combined with a non-metallic solvent catalyst that is a carbonate, such as sodium carbonate. In one example, the amount of sodium carbonate used may be sufficient to form a fully sintered carbonate PCD (CPCD) body, for example up to 5% by weight based on the total weight of the carbonate catalyst and diamond abrasive grains. It is believed that the billet made with sodium carbonate is inherently less dark than cobalt PCD, which contributes to the higher levels of luminescence emission and intensity, as dark materials exhibit visible light absorption. In some embodiments, it may be desirable to use less amount of catalyst material than is useful for forming a fully sintered PCD body, for example less than 5% by weight catalyst (relative to the total weight of the diamond layer or PCD body). In these and other such embodiments, it may be desirable to produce a partially sintered or semi-sintered body of PCD, which contains both intercrystalline bonded diamond and free diamond abrasive grains, for the purpose of facilitating downstream processes of particle size classification of the PCD body into nano-sized diamond flakes or abrasive grains, as better described below.

[0066] When diamond grains are consolidated under HPHT conditions, plastic deformation can occur due to shear stress caused by point contacts between diamond grains or particles. It may be useful to heat diamond grains to create a large number or high concentration of voids, but the high temperature of HPHT can also cause diamond graphenization because most of the diamond particle surface (voids in the compact) is not subjected to pressure. These voids on the diamond surface in the compact may require or benefit from the application of pressure to avoid diamond graphenization. In an attempt to minimize unwanted diamond graphenization while maintaining the desired amount of plastic deformation to create nitrogen centers or vacancies, it is useful to use an optimal range of catalyst materials, such as sodium carbonate. A range of catalyst materials is developed to balance the shear stress applied by point contacts between particles to create plastic deformation and voids, and the hydraulic pressure from the catalyst material melt located between diamond particles to limit or even prevent diamond graphenization.

[0067] FIG. 8 is a graph 90 showing the effect of luminescent diamond having optical emission intensity in the green wavelength spectrum excited by a 473 nm laser as a function of diamond content for diamond pellets formed by sintering 12 μm-22 μm diamond abrasive grains and sodium carbonate at about 2200° C. As shown in the graph, the optical emission intensity of the luminescent diamond decreases when the diamond abrasive grains or particles are mixed with more than about 30 wt% sodium carbonate. Sodium carbonate melts at temperatures above 1400° C. at sintering pressures between about 5 GPa and 7 GPa. When sodium carbonate content is used above about 30 wt%, the diamond particles are completely surrounded by the sodium carbonate melt, resulting in fewer direct diamond / diamond point contacts during HPHT sintering. This results in fewer nitrogen vacancy centers being created inside the diamond lattice due to less shear stress being applied to the diamond particles for plastic deformation. Fewer nitrogen vacancy centers also result in fewer NVN optical centers inside the diamond particles, which explains the decrease in green optical emission intensity within increased sodium carbonate content. A significant drop in green light emission intensity also occurs when the sodium carbonate content is less than about 20 wt%. At low sodium carbonate content, more direct diamond / diamond grain point contact occurs, but there is not enough sodium carbonate to cover the diamond pressure free surface during HPHT sintering. Therefore, the uncovered diamond surface is more likely to be graphenized after sintering.

[0068] FIG. 9 shows the fracture surfaces of sintered diamond pellets 100, 102, 104, 106, and 108 formed by the method described above with reference to FIG. 8, with different diamond (diamond grit and sodium carbonate) contents. Diamond pellet 100 has a diamond content of 70 wt% or 30 wt% sodium carbonate, diamond pellet 102 has a diamond content of 75 wt% or 25 wt% sodium carbonate, diamond pellet 104 has a diamond content of 80 wt% or 20 wt% sodium carbonate, diamond pellet 106 has a diamond content of 85 wt% or 15 wt% sodium carbonate, and diamond pellet 108 has a diamond content of 90 wt% or 10 wt% sodium carbonate. As shown, as the diamond content increases, the color of the diamond pellets becomes darker. This is related to the graphenization of diamond described above. When the diamond content is 85 wt%, the sintered diamond pellets 106 are gray in color, which corresponds to the identified drop in luminescence intensity for diamond at 85 wt% diamond content shown in Figure 8. Therefore, based on this information, the optimum composition range is between about 75 wt% and 80 wt% diamond content, although such composition may vary based on several factors, including desired luminescence, catalyst materials, etc.

[0069] The manner in which the diamond particles and sodium carbonate are bonded can also play a role, as the emission intensity can also be relied upon to limit how much diamond graphenization is prevented and how much shear stress the diamond particles are subjected to during HPHT sintering. In one example, it may be desirable to have a uniform mixture between the diamond abrasive or particles and the sodium carbide material based on the total weight of the diamond abrasive and sodium carbonate (e.g., a non-uniform mixture may function to shift the optimal composition window from the desired diamond content (e.g., 75wt%-80wt%)). In most cases, more sodium carbonate may be required to prevent diamond graphenization in situations where the combination or mixture of diamond abrasive and sodium carbonate is less uniform. It should be understood that although a particular optimal diamond content window is provided, the use of different types of non-catalytic solvents (e.g., other than sodium carbonate) will also have different optimal sintering compositions.

[0070] In one example, the luminescent diamond produced by the HPHT process disclosed herein may have a diamond content of 70-100 wt%, 80-95 wt%, greater than 80 wt%, and in a particular example, about 85 wt%, based on the total weight of diamond and catalyst material (e.g., sodium carbonate), optimizing the diamond content to provide a desired amount of green light emission intensity. In one example, the light emission intensity is determined from the luminescent diamond provided in the form of a suspension of the luminescent diamond in water, such a form may be related to a particular use application, such as a medical diagnostic application. In such an example, it has been found that the luminescent diamond having a higher diamond content (e.g., greater than about 80 wt%) as described above provides a desired higher amount of light emission intensity when provided in the form of a suspension.

[0071] In one example, luminescent diamonds containing increased diamond content, for example above about 80 wt%, are formed using a mixture of diamond abrasive grains having an average particle size of 12 μm to 22 μm combined with a carbonate catalyst such as sodium carbonate. The mixture is subjected to the above HPHT processing conditions with or without the introduction of asymmetric or differential pressure through the cell or press. In one example, the HPHT process used is a process carried out at a temperature of about 2200° C. and without the application of asymmetric or differential pressure. The resulting luminescent diamond is provided in the form of pellets containing the luminescent diamond. The luminescent diamond pellets are washed to remove sodium carbonate for the purpose of preparing the desired luminescent diamond suspension. In one example, the material used to wash the pellets depends on the type of catalyst present in the luminescent diamond pellets and the type of catalyst that solubilizes the catalytic material for removal from the luminescent diamond pellets. In one example, where the catalyst is sodium carbonate, water is used to wash the luminescent diamond pellets to remove the sodium carbonate. In one example, the luminescent diamond pellets are placed in heated or boiling water during the washing process. The washed luminescent diamond pellets are then milled or otherwise reduced in size to produce nano-sized luminescent diamond particles. In one example, the luminescent diamond particles are size-classified to particles having an average particle size of about 100 nanometers. Although specific particle sizes are disclosed, it is understood that the luminescent diamond particles may be size-classified to particles larger or smaller than 100 nanometers with similar characteristics in photoluminescence and maintain the desired brightness. In one example, the nano-sized luminescent diamond particles are heat-treated at a temperature of about 400-550°C in an air environment. The heat-treatment temperature will vary depending on the specific particle size of the luminescent diamond particles, for example, larger particle size luminescent diamond particles may be heat-treated at a higher temperature than smaller particle size luminescent diamond particles.In one example, where the luminescent diamond particles have an average particle size of about 100 nanometers, the heat treatment temperature may be about 500-525°C.

[0072] FIG. 10-1 is a graph 110 of the optical emission response 112 of 100 nanometer luminescent diamond irradiated with a 473 nm laser in a 0.1 wt% suspension in deionized water. The nanodiamond material was created by HPHT treating a mixture of about 85% 12-22 μm diamond and about 15% sodium carbonate, followed by rinsing to remove the sodium carbonate, milling the diamond to about 100 nm, and heat treating at about 515° C. The maximum optical emission intensity 114 was observed at wavelengths between about 520-550 nm.

[0073] FIG. 10-2 is a graph 120 showing the effect of luminescent diamond having a maximum light emission intensity in the green wavelength spectrum excited by a 473 nm laser for the 100 nm luminescent diamond particles disclosed above given in the form of an aqueous suspension. The luminescent diamond materials were made by HPHT treatment of various compositions of 12-22 μm diamond and sodium carbonate, which were about 70%-100% diamond and the remainder sodium carbonate. In one example, a luminescent diamond suspension was prepared by dispersing 100 nm luminescent diamond particles in deionized water to form a 0.1 wt% suspension (i.e., containing 0.1 wt% 100 nm luminescent diamond particles based on the total weight of the particles and water). As shown in graph 120, the light emission intensity of the luminescent diamond solution appears to improve as the diamond content increases from about 70 wt% during the HPHT treatment, reaching a maximum light emission intensity at about 85 wt%. All samples had maximum emission intensities between about 520 and 550 nanometers, similar to those shown in FIG. 10-1 above.

[0074] The light emission intensity of two different luminescent diamond suspensions is shown in FIG. 10-2, one suspension 122 contains diamond particles heat treated at about 500° C., and another suspension 124 contains diamond particles heat treated at about 515° C. As shown, the luminescent diamond suspension with about 85 wt. % diamond heat treated at about 515° C. exhibits higher light emission intensity than the luminescent diamond suspension with about 85 wt. % diamond heat treated at a lower temperature of about 500° C. This result shows the beneficial effect of heat treatment at higher temperatures on increasing light emission intensity. However, it is significant that the heat treatment temperature may cause the luminescent diamond to graphenize, which in turn acts to reduce or lower the light emission intensity. Therefore, it is desirable that the nano-sized luminescent diamond particles provided in the suspension are heat treated within the disclosed temperature ranges in order to optimize the light emission intensity and not cause unwanted diamond graphenization. Indeed, in some embodiments, the temperature of heat treatment can be important to obtain the desired light emission intensity. Also, if the diamond particles are dark in color (i.e., due to graphite) before heat treatment, heat treatment in the temperature range disclosed above serves to burn out (e.g., burn out) the graphite layer and increase the light emission intensity. However, in at least some embodiments, it is desirable that the heat treatment temperature is not too high to prevent the diamond particles from burning out. Thus, the heat treatment temperature range provided above serves to balance the potential advantage of obtaining increased light emission intensity without the potential disadvantage of having diamond weight loss due to diamond burning out. In one example, a heat treatment temperature of about 500°C provides this balance, while ensuring that the diamond particles do not darken (i.e., do not graphitize) during the heat treatment process or cycle.

[0075] As shown in graph 120 of Fig. 10-2, the light emission intensity of luminescent diamond suspension starts to decrease when diamond content exceeds about 85wt%.However, the light emission intensity of luminescent diamond suspension with 90wt% and even 100wt% is shown to be greater than the light emission intensity of luminescent diamond suspension with only 70wt% diamond.Therefore, this graph 120 helps to explain the positive effect that increasing diamond content, for example above about 80wt%, leads to the increase in the light emission intensity of nano-sized luminescent diamond disclosed herein that is provided in the form of suspension.

[0076] Any suitable method may be used in measuring the light emission intensity. For example, time resolved photoluminescence may be used to excite the sample with a light pulse and measure the decay over time. The peak intensity over the measurement period may be used. Of course, other methods may also be used. In some embodiments, the intensity may be a unitless measurement or may be normalized so that it is unitless.

[0077] Although some exemplary embodiments of luminescent diamond have been described in detail above, those skilled in the art will easily understand that many modifications are possible in the exemplary embodiments without substantially departing from the scope of the claims and the present disclosure. For example, the luminescent diamond disclosed herein is presented in the context of biological end-use applications. It should be understood that the luminescent diamond disclosed herein may be used in end-use applications other than biological applications where a desired improved level of luminescence intensity is useful or beneficial. Other potential applications of luminescent diamond (e.g., those containing nitrogen vacancy centers) include, but are not limited to, magnetic sensors, high resolution thermography, microscopic sensor arrays, anti-counterfeiting measures, ion concentration monitoring, membrane potential measurement, optical traps, and strain / pressure sensors. It is therefore understood that the luminescent diamond disclosed herein is not intended to be limited to one particular end-use application.

[0078] In other embodiments, the HPHT conditions described are merely exemplary, since different HPHT conditions may be used. For example, the materials described herein may be formed using different pressing techniques, in the presence of different catalyst materials, or with a myriad of other variations. Thus, pressure or temperature conditions may vary in different embodiments. For example, one HPHT press design may use different conditions than a different HPHT press design. Thus, variations in the process and end use applications of luminescent diamond are intended to be included within the scope of the present disclosure, as defined in the following claims.

[0079] In the description herein, various relational terms may be used to facilitate understanding of various aspects of some embodiments of the present disclosure. Relational terms such as "top", "bottom", "upper", "lower", "left", "right" and the like may be used to describe various components, including their operational or illustrated positions relative to one or more other components. The relational terms do not dictate a particular orientation for each embodiment within the scope of the present specification or claims, but are intended as a convenience in facilitating reference to the various components. Thus, aspects of such relations may be reversed, inverted, rotated, moved in space, placed in a diagonal orientation or position, placed horizontally or vertically, or similarly altered.

[0080] A particular description or designation of an element as a "first," "second," "third," etc. may be used in the specification or claims to distinguish between identical elements or elements that are similar in use, structure, or operation. Such language is not intended to limit the element to a singular designation or to require a plurality of elements. Thus, an element referred to herein as a "first" element may be the same as or different from an element referred to in a claim as a "first" element, and a claim may include a "first" element without requiring the presence of a "second" element.

[0081] Furthermore, the specification or claims may refer to "additional" or "other" elements, features, aspects, components, etc., without excluding the presence of a single or multiple elements of the additional elements. When a claim or the specification refers to "a" or "an" element, such reference is not to be construed as referring to only one of that element, but instead encompasses other components and is understood as "at least one" of that element. When a component, feature, structure, function, or characteristic is described herein as "may include," "may include," "can include," or "potentially include," that particular component, feature, structure, or characteristic is provided in one particular embodiment, but is optional in other embodiments of the disclosure. The terms "couple," "coupled," "connect," "connected," "connected," "connected with," and "connecting" refer to "directly connected with" or "connected with via one or more intermediate elements or members." "Integral" or "integrally" formed components include components made from the same piece or set of materials, such as by being generally molded or cast from the same material in the same molding or casting process, or generally machined from the same stock material. It is also understood that components that are "integral" are "bonded" together.

[0082] Furthermore, it should be understood that references to "one embodiment," "one embodiment," or "one example" in the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments or examples that also incorporate the recited features. For example, any element described in connection with an embodiment herein may be combinable with any element of any other embodiment described herein.

[0083] Any number, percentage, ratio, or other value described herein is intended to include not only that value, but also other values ​​that are "about" or "approximately" the described value, as understood by those of ordinary skill in the art, that are encompassed by the embodiments of the present disclosure. Thus, the described value should be interpreted broadly enough to encompass values ​​that are at least close enough to the described value to perform the desired function or achieve the desired result. The described value includes at least expected variation during a suitable manufacturing or production process, and may include values ​​within 5%, within 1%, within 0.1%, or within 0.01% of the described value.

[0084] As used herein, the terms "approximately," "about," and "substantially" refer to an amount that is close to a stated amount, within standard manufacturing or process tolerances, or that still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," and "substantially" may refer to an amount that is within less than 5%, within less than 1%, within less than 0.1%, and within less than 0.01% of a stated amount. Furthermore, any directions or frames of reference in the foregoing specification should be understood to be relative directions or movements only. For example, any reference to "top" and "bottom," or "above" or "below" merely describes the relative location or movement of the associated elements.

[0085] Although various exemplary embodiments have been described in detail herein, those skilled in the art will readily appreciate in view of the present disclosure that many modifications are possible in the exemplary embodiments without substantially departing from the present disclosure. Any such modifications are therefore intended to be included within the scope of the present disclosure. Similarly, although the present disclosure herein contains many details, these details should not be interpreted as limiting either the scope of the present disclosure or the scope of the appended claims, but merely as providing information regarding one or more specific embodiments that may be included within the scope of the present disclosure and the scope of the appended claims. Any described features from the various disclosed embodiments may be used in combination.

[0086] In the claims, means-plus-function clauses are intended to cover equivalent structures, as well as the structures described herein as performing the described function, and structural equivalents. Thus, while nails and screws may not be structural equivalents in that nails use cylindrical surfaces to fasten wooden pieces together, whereas screws use helical surfaces, in the context of fastening wooden pieces, nails and screws may be equivalent structures. It is Applicant's express intent not to invoke the claimed means-plus-function type for any limitation of any of the claims herein, except where the claim expressly uses the words "means for" with the relevant function.

[0087] The Abstract at the end of this disclosure is provided to enable the reader to quickly grasp the general nature of some embodiments of the disclosure, and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. 1. A method of making a luminescent diamond, comprising: placing a volume of precursor diamond abrasive grains and catalytic material into a pressure cell; subjecting the pressure cell to high pressure / high temperature conditions to form one or more diamond pellets subjected to differential strain; A method comprising:

2. subjecting the pressure cell to high pressure / high temperature conditions includes applying axial and radial pressure to the volume of precursor diamond abrasive grains and catalytic material; The axial pressure is different from the radial pressure and imparts the differential strain on the one or more diamond pellets.

2. The method of claim 1 .

3. the axial pressure is greater than the radial pressure; The resulting one or more diamond pellets have a negative strain in the axial direction and a positive strain in the radial direction.

3. The method of claim 2.

4. the radial pressure is greater than the axial pressure; The one or more diamond pellets have a negative strain in the radial direction and a positive strain in the axial direction.

3. The method of claim 2.

5. The one or more diamond pellets have an aspect ratio, measured between their radial and axial dimensions, greater than 1 or experience a change in aspect ratio due to the pressure cell being subjected to high pressure / high temperature conditions.

2. The method of claim 1 .

6. Subjecting the pressure cell to high pressure / temperature conditions includes using the pressure cell to apply an axial pressure on the volume of the precursor diamond abrasive grains and catalytic material that is different from the radial pressure.

3. The method of claim 2.

7. subjecting the pressure cell to high pressure / temperature conditions includes applying a pressure force to the pressure cell using a pressure device; The pressure device is configured to apply an axial pressure on the pressure cell that is different from a radial pressure.

3. The method of claim 2.

8. The step of subjecting the pressure cell to high pressure / high temperature conditions is carried out at a temperature of 1,800° C. or less.

2. The method of claim 1 .

9. subjecting the pressure cell to high pressure / high temperature conditions includes subjecting the diamond abrasive grains to plastic deformation to create vacancies that promote the formation of nitrogen vacancy centers; The resulting diamond pellets have greater luminescence in the red wavelength spectrum than diamond pellets that have been subjected to non-differential strain during high pressure / high temperature conditions.

2. The method of claim 1 .

10. A diamond pellet, a volume of precursor diamond abrasive grains and catalytic material is subjected to high pressure / high temperature conditions to form the diamond pellet under differential strain; and nitrogen vacancy centers having a greater number or concentration of NV centers compared to NVN centers, N3 centers, or a combination of NVN centers and N3 centers. Diamond pellets characterized by:

11. The diamond pellet has a positive strain taken along one of the axial or radial dimensions and a negative strain taken along the other of the axial or radial dimensions.

11. The diamond pellet according to claim 10.

12. The diamond pellet has an aspect ratio, measured between its radial and axial dimensions, greater than 1.

12. The diamond pellet according to claim 10 or 11.

13. The diamond pellets emit with greater luminance in the red wavelength spectrum than in the green wavelength spectrum.

12. The diamond pellet according to claim 10 or 11.

14. 1. A method for making diamond pellets, comprising: subjecting a volume of diamond abrasive grains and catalytic material to a high pressure / high temperature process to produce said diamond pellets; During the high pressure / high temperature process, the volume of diamond abrasive grain and catalytic material is subjected to a pressure differential comprising an axial pressure that is different from a radial pressure; The pressure differential induces a greater degree of plastic deformation in the diamond pellet than in a high pressure / high temperature process where the axial and radial pressures are approximately equal. A method characterized by:

15. The pressure differential subjects the diamond pellet to a differential strain that is positive in one dimension and negative in another dimension.

15. The method of claim 14.

16. The diamond pellet has a greater number or concentration of NV centers than NVN centers, N3 centers, or both NVN centers and N3 centers.

15. The method of claim 14.

17. The diamond pellets emit a greater amount of light in the red wavelength spectrum than in the green wavelength spectrum.

15. The method of claim 14.

18. The volume of diamond abrasive and catalytic material is within a pressure cell configured to provide the pressure differential.

15. The method of claim 14.

19. The volume of diamond abrasive grains is in a pressure cell contained in a pressure device; The pressure device is configured to provide at least a portion of the pressure differential.

15. The method of claim 14.

20. The diamond pellet has an aspect ratio or undergoes an aspect ratio change greater than 1 measured between the vertical dimensions of the diamond pellet.

15. The method of claim 14.

21. 1. A pressure cell for use in a high pressure / high temperature press, comprising: at least one axial component; at least one radial component; an interior chamber defined by the at least one axial component and the at least one radial component; Equipped with The at least one axial component and the at least one radial component are configured to generate asymmetric axial and radial pressures on the interior chamber from symmetric pressures on outer surfaces of the at least one axial component and the at least one radial component. A pressure cell characterized by:

22. The at least one axial component comprises an incompressible material.

22. The pressure cell of claim 21.

23. The at least one radial component comprises a loose powder or granulated material.

23. A pressure cell according to claim 21 or claim 22.

24. 1. A high pressure / high temperature press comprising: a pressurizing component configured to apply asymmetric pressure on a pressure cell within the press such that an axial pressure is different from a radial pressure; A high pressure / high temperature press characterized by:

25. The pressurizing component comprises: Anvil, heating unit, or power supply, Contains at least one of 25. The high pressure / high temperature press of claim 24.

26. temperature sensors, pressure sensor, or a controller configured and arranged to control at least one of the pressure or temperature within said pressure cell; Further comprising at least one of 26. A high pressure / high temperature press according to claim 24 or claim 25.

27. 1. A method of making a luminescent diamond pellet, comprising: placing a volume of precursor diamond abrasive grains and catalytic material into a pressure cell; subjecting the pressure cell to high pressure / high temperature conditions to form one or more luminescent diamond pellets, the luminescent diamond pellets having a diamond content greater than about 80 wt%; A method comprising:

28. The luminescent diamond pellets have a diamond content of about 80-95 wt %.

28. The method of claim 27.

29. The luminescent diamond pellets have a diamond content of about 85 wt%.

29. The method of claim 28.

30. reducing the luminescent diamond pellets to nano-sized luminescent diamond particles having an average particle size of about 100 nanometers or less.

28. The method of claim 27 further comprising:

31. washing the nano-sized luminescent diamond particles in a solution. Further provided with The solution solubilizes and removes the catalytic material therefrom.

31. The method of claim 30.

32. The aqueous suspension has a maximum light emission intensity between about 520 and 550 nanometers in the green wavelength spectrum.

32. The method of claim 31 .

33. heat treating the washed nano-sized luminescent diamond particles at a temperature of about 400-550°C.

31. The method of claim 30 further comprising:

34. forming an aqueous suspension of said nano-sized luminescent diamond particles; Further provided with the aqueous suspension comprising approximately 0.1 wt % luminescent diamond based on the total weight of the suspension; The suspension has a maximum light emission intensity in the green wavelength spectrum under excitation of a 473 nanometer laser that is greater than about 510 nanometers.

31. The method of claim 30.

35. 1. A method for making an aqueous suspension of nanometer-sized luminescent diamond particles, comprising: reducing the size of luminescent diamond pellets formed by a high pressure / high temperature process to luminescent diamond particles having an average particle size of nanometer size, said luminescent diamond pellets having a diamond content of 80-95 wt % based on the total weight of diamond and catalyst material used to make said luminescent diamond pellets; washing the nanometer-sized luminescent diamond particles with a material that solubilizes the catalytic material for removal; heat treating the washed nanometer-sized luminescent diamond particles; combining an amount of the heat-treated nanometer-sized luminescent diamond particles with water to form an aqueous suspension of nanometer-sized luminescent diamond particles; A method comprising:

36. During the reducing step, the luminescent diamond pellets are reduced to luminescent diamond having an average particle size of about 100 nanometers or less.

36. The method of claim 35.

37. The luminescent diamond pellets have a diamond content of about 85 wt%.

36. The method of claim 35.

38. During the heat treatment step, the nanometer-sized luminescent diamond particles are subjected to a temperature of 400-550°C.

36. The method of claim 35.

39. the catalytic material is sodium carbonate; The washing step comprises exposing the luminescent diamond particles to water.

36. The method of claim 35.

40. The aqueous suspension of nanometer-sized luminescent diamond particles comprises about 0.1 wt % of nanometer-sized luminescent diamond particles based on the total weight of the aqueous suspension.

36. The method of claim 35.

41. The aqueous suspension has a maximum light emission intensity in the green wavelength spectrum under excitation of a 473 nanometer laser, greater than about 510 nanometers.

41. The method of claim 40.

42. The aqueous suspension has a maximum light emission intensity of about 520 to 550 nanometers within the green wavelength spectrum.

42. The method of claim 41 .

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