Nanodiamond with vacancy defect and quantum dot luminescence

Abstract

Luminescent diamond is made by subjecting a volume of diamond grains to high pressure / high temperature conditions with or without a catalyst or pressure transfer medium to undergo plastic deformation of the grains to create internal vacancy defects, thereby increasing the luminescent activity / strength of the resulting diamond material. The luminescent material is then subjected to a further treatment to produce quantum dots on the surface of the diamond particles. Quantum dot formation may include placing the diamond particles in a liquid, and subjecting the particles to laser pulses. The consolidated diamond material may be treated to further increase luminescent activity / intensity, including reduction of the consolidated diamond material to diamond particles, heat treatment in vacuum, and / or air heat treatment. The resulting luminescent diamond particles exhibit a higher luminous intensity level than that of conventional luminescent nanodiamonds, and can be functionalized for use in biological applications.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 366,434, filed on June 15, 2022, entitled “NANODIAMOND WITH VACANCY DEFECT AND QUANTUM DOT LUMINESCENCE,” the disclosure of which is hereby incorporated by reference into this document. Background Art

[0003] Laser injected fluorescence is a known technique used to better understand how biological systems function at the molecular level by probing biological molecules individually for observation. In examples, laser injected fluorescence can be applied to imaging and tracking individual molecules or particles in biological cells and the like, for example, in vivo biosensors for internal organ mapping, cell imaging, and the like. One substance used for laser injected fluorescence is luminescent nanodiamonds, which are nanometer-sized diamond particles or grains that have been developed to emit light when excited by a light source within the desired wavelength required by the end-use application. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] These and other features and advantages of the luminescent nanodiamonds and methods of making the same as disclosed herein will be appreciated as they will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0005] Figure 1 is a schematic diagram of a diamond nanoparticle having nitrogen vacancy centers and quantum dot light emitting sites according to an embodiment of the present disclosure; and

[0006] Figure 2 Quantum dot fabrication using femtosecond laser pulses and a carbon source in liquid according to an embodiment of the present disclosure is schematically illustrated. DETAILED DESCRIPTION

[0007] In some embodiments, luminescent diamonds (e.g., photoluminescent diamonds) and methods of making the same as disclosed herein are designed in a manner that increases the luminescence and functional utility of nanodiamonds. Luminescent diamonds prepared according to the principles disclosed herein may exhibit luminescence intensity levels similar to or higher than those of conventional luminescent diamonds, thereby providing an opportunity to expand the potential end-use application range of such materials. In some embodiments, luminescent diamonds are initially formed by consolidation and compaction of pre-existing diamond grains, forming a luminescent active sintered body or block (characterized by a high degree of intercrystalline diamond bonding) or forming a mechanically combined semi-sintered body or block (characterized by essentially no intercrystalline diamond bonding). In this case, the consolidated material may be referred to as luminescent diamond. During subsequent procedures, the size of the luminescent diamond may be reduced according to the requirements of a particular end-use, and in some embodiments, the size of the resulting diamond particles or grains is nanoscale. In some embodiments, the size-reduced luminescent diamond may be only nano-sized particles or may include a combination of nano-sized particles and coarser diamond particles. As used herein, the term "nanodiamond" is understood to refer to luminescent diamond comprising nano-sized diamond particles (ie, having an average size between about 1 and 1000 nm).

[0008] In other embodiments, compacted and consolidated diamond (before or after particle size reduction) may also be modified using processes such as laser irradiation to produce luminescent centers on the surface of these materials. Laser irradiation may follow the so-called quantum carbon dot method, in which carbon-based materials can produce luminescence. The production of quantum carbon dots may include subjecting compacted and consolidated diamond materials containing nitrogen vacancies to high-energy laser pulses. These laser pulses produce active luminescent centers on the surface of the nanodiamond, while the nitrogen vacancy centers are dispersed throughout the interior (and possibly the surface) of the nanodiamond. The number and size of the quantum dots and the parameters of the laser treatment may provide added luminescent intensity benefits beyond those produced by nitrogen vacancy centers or quantum carbon dots alone.

[0009] In some embodiments, luminescent diamonds as disclosed herein may be formed by combining a volume of precursor diamond grains, which may be in the form of natural and / or synthetic diamond grains, and placing the volume of diamond grains in a can or container conventionally used for diamond grain consolidation. In some embodiments, the diamond grains may have an average grain size of about 1 μm to 1000 μm, about 1 μm to 100 μm, or about 10 μm to 50 μm. In other embodiments, the initial diamond grain or powder size may extend to the submicron or nanodiamond range. In some embodiments, nano-sized powders formed by mechanical crushing or detonation processes of conventional diamond powders may be employed in a similar manner.

[0010] Conventional diamond powders may be of synthetic or natural origin, however, synthetic diamond powders typically have a higher intrinsic nitrogen content, which together with adjacent vacancies renders the diamond luminescently active. In some embodiments, it is desirable that the starting diamond material have an intrinsic amount of nitrogen impurities consistent with the amount found in diamonds designated as type 1b, for example, about 50 ppm nitrogen or more. Nano-sized powders synthesized by impact synthesis also typically have a higher intrinsic nitrogen content. In some embodiments, the container and its contents are subjected to a high pressure / high temperature (HPHT) consolidation process using conventional pressing equipment for making polycrystalline diamond. In some embodiments, the volume of diamond grains is placed in a can or container. The can or container may be sealed or unsealed, placed in an HPHT press, and then subjected to the desired sintering pressure and temperature conditions.

[0011] In some embodiments, the HPHT process temperature may be in the range of about 1300°C to 2500°C, and the process pressure may be about 3.0 GPa to about 10 GPa. In some embodiments, the volume of diamond grains is substantially free of any catalyst material, such that the diamond material produced by the HPHT process is not fully sintered, but is in the form of a semi-sintered mass or body comprising diamond grains mechanically held together by frictional contact, cold welding, diamond self-diffusion, or the like. In some embodiments, an incompletely sintered (i.e., semi-sintered and not characterized by a network of diamond grains bonded together using a conventional metal solvent catalyst) diamond material is produced that has an improved relative transparency compared to a sintered polycrystalline diamond body. The transparency of the diamond material may increase the intensity of the luminescent emission therefrom. There may also be graphite formed in porous regions of the semi-sintered body, which may reduce the luminescent intensity. In such cases, it is desirable that the graphite material be partially or completely removed as part of the manufacturing process.

[0012] During the HPHT process, it has been found that at least a portion of the volume of precursor diamond grains undergoes plastic deformation. In some embodiments, the extent of the HPHT consolidation process is such that sufficient plastic deformation is induced in the diamond grains to produce nitrogen vacancy (NV and / or NVN) defects and / or N3 optical centers in the diamond grains for rendering the diamond grains luminescently active. Plastic deformation of the diamond particles during HPHT is believed to produce vacancies because deformation mechanisms such as crystal dislocation motion become active. Vacancies, in turn, may combine with nitrogen impurities to form nitrogen vacancy (NV and / or NVN) defects and / or N3 optical centers that produce the desired luminescent activity. In some embodiments, this occurs during conventional sintering of polycrystalline diamond with a metal catalyst such as cobalt that acts to promote intercrystalline diamond bonding during the HPHT process or a non-metallic catalyst / pressure transmission medium such as carbonates and chlorides that do not promote intercrystalline diamond bonding during the HPHT process. In some embodiments, diamond grains produced by the HPHT process may undergo severe plastic deformation, with extensive NV and / or NVN defects and / or N3 optical centers, and weak diamond-diamond bonding compared to solvent catalyst bonded polycrystalline diamond. For example, in some embodiments, it is desirable for the diamond grains to induce such plastic deformation that produces luminescence activity during the HPHT process without producing a fully sintered body. By avoiding a fully sintered body, downstream processes such as sizing the diamond grains by a crushing process become easier and less energy intensive, as only mechanically bonded diamond grains need to be separated.

[0013] In some embodiments, luminescent diamond as disclosed herein may be formed in a similar manner by subjecting a volume of diamond or other superhard precursor grains to an HPHT process, wherein the precursor material has an inherent amount of silicon impurities. In this case, luminescent diamond may be formed by silicon vacancies and optical centers used to render the diamond grains luminescently active. Other impurities that may produce vacancies that produce luminescence in a suitable spectrum (e.g., visible, ultraviolet, infrared, near infrared, etc.) may also be used.

[0014] In some embodiments, luminescent diamond as disclosed herein may be formed in a similar manner by subjecting a volume of diamond precursor grains to an HPHT process in the presence of a catalyst material. In such embodiments, the type of catalyst material used may be selected from the group including, but not limited to, Co, Fe, Ni, carbonates, Si, and combinations thereof, for forming polycrystalline diamond (PCD). In some embodiments, HPHT treatment conditions for cobalt PCD may be within a temperature of about 1300° C. to 1500° C. and a pressure of about 5.0 GPa to 7.5 GPa. In addition, cobalt PCD is typically heat treated in a vacuum at a temperature of 600° C. to 700° C. (e.g., after PCD formation, before sizing, and / or after). The amount of catalyst material used may and will vary depending on factors such as the type of catalyst used, the desired amount of luminescence, and the particular end-use application.

[0015] In biological end-use applications, the presence of metallic materials in the luminescent diamond may not be desired and / or permitted for biocompatibility reasons, in which case it may be desirable to use a non-metallic catalyst. In some embodiments, the use of a non-metallic catalyst results in a PCD body having relatively higher transparency or reduced opacity compared to PCD formed using a metal solvent catalyst. In some embodiments, non-metallic catalysts that can be used to make luminescent diamond as disclosed herein include carbonate catalysts, such as magnesium carbonate, calcium carbonate, etc., resulting in the formation of carbonate PCD (CPCD). In some embodiments, the amount of such carbonate catalyst can be an amount sufficient to form a fully sintered carbonate PCD body, for example, up to about 5% by weight based on the total weight of the carbonate catalyst and diamond grains. Carbonate PCD appears to be inherently brighter / more transparent than cobalt PCD, which is believed to contribute to higher luminescent emission and intensity levels. In some embodiments, HPHT treatment of carbonate PCD can be carried out at a temperature of about 1700°C to 3000°C and a pressure greater than about 7.0 GPa. In addition, carbonate PCD may be heat treated in an inert or vacuum environment to a temperature of about 500°C to 1300°C (e.g., after CPCD formation, before and / or after sizing). As with the previously described embodiments, HPHT treatment of CPCD produces plastic deformation in the diamond grains, thereby producing vacancies or optical centers (e.g., nitrogen, silicon, etc.) that cause increased levels of luminescence activity / intensity compared to the precursor diamond grains. Some of the vacancies formed during HPHT may not combine with nitrogen, silicon or other impurities during the plastic deformation process, and may migrate to the vicinity of the site during the heat treatment, thereby producing additional vacancies or optical sites. The higher processing temperature and pressure conditions involved in carbonate PCD may produce a higher degree of plastic deformation in the diamond grains, and therefore produce higher luminescence activity. The use of higher heat treatment temperatures may also promote the generation of additional defects or optical centers, and therefore promote higher luminescence activity.

[0016] Figure 1 Schematically illustrates a diamond nanoparticle 100 that can provide luminescence from vacancies 102, surface quantum dots 104, or a combination thereof. In particular, nitrogen, silicon, or other vacancies or optical centers can be dispersed throughout the body 106 of the diamond nanoparticle 100. Additionally or alternatively, quantum dots 104 can be formed on the surface of the body 106 of the diamond nanoparticle.

[0017] This hybrid method including vacancy / optical center and quantum dot can be used to increase luminescence.For example, as particle becomes smaller, luminescent nanodiamond may lose considerable intensity.For example, a particle size less than 100nm, less than 50nm or less than 35nm may need higher luminous intensity in some applications, and may benefit from polytype luminescence.Therefore, luminescence from two independent mechanisms may have the potential to increase the overall intensity of nanoparticles, and make it more visible in biological or other applications.

[0018] Figure 2 Schematically illustrated is a method for producing quantum dots, wherein quantum dot fabrication includes placing a carbon source 208 in a liquid at 210 and subjecting the carbon source 208 to a laser pulse 212. In some embodiments, the laser pulse is a femtosecond laser pulse and has different intensities, wavelengths, etc., depending on the desired properties for a particular application or end use. The carbon source 208 may include diamond nanoparticles, diamond chunks, or other materials including nitrogen vacancies (e.g., NV, NVN, N3), silicon vacancies, or other types of luminescent vacancy centers as discussed herein. In other embodiments, the carbon source 208 may include diamond particles that have not been treated to form vacancies. Quantum dots may be produced, and the particles may then be consolidated and compacted (e.g., using a HPHT process) to form vacancy centers.

[0019] The claims and all exhibits are incorporated herein as part of this disclosure. All features described in this disclosure (including exhibits and claims) may be combined with any other features or components unless expressly described as mutually exclusive. Systems and methods for making luminescent diamonds are described in U.S. Patent Application Publication US2022 / 0056337, U.S. Patent Application No. 18 / 005,115, International Patent Application PCT / US2022 / 052223, and International Patent Application PCT / US2023 / 023697, each of which is incorporated herein by reference in its entirety for all purposes.

[0020] For use of luminescent diamonds as disclosed herein in certain downstream applications (such as biological uses), it may be desirable to further treat or functionalize the luminescent diamond particles (e.g., nanodiamonds) to adapt the material for its intended use. The treatment regime and type that may be used to functionalize the luminescent diamond material as disclosed herein should be understood to vary depending on the specific end-use application. However, an exemplary functionalization process may be one involving oxygen termination along the diamond surface to render the diamond surface hydrophilic, and may be established through a series of surface oxidation processes. Such oxygen-terminated functionalization may include providing a mixture of =O, -OH, -COOH, or -COC- groups on the surface. Other surface terminations may include hydrogen termination, halogenation, thermal annealing to produce double bonds, and reduction to OH termination. Another type of functionalization may involve grafting or attaching certain molecules to a treated diamond surface such as treated in a manner to promote such attachment, wherein such molecules are selected to readily react with different biomolecules. Yet another type of functionalization may include biomarkers, which may occur through electrostatic (non-covalent) or covalent binding attachment between diamond particles and biomolecules. These are just a few of the ways in which luminescent diamonds as disclosed herein may be functionalized for use in biological applications, and it will be appreciated that other known methods and techniques that may be used to functionalize luminescent diamonds for specific biological uses are within the scope and spirit of the present disclosure.

[0021] Although only a few example embodiments of luminescent diamonds are described in detail above, it will be readily apparent to those skilled in the art that many modifications may be made in the example embodiments without substantially departing from the present invention. For example, luminescent diamonds as disclosed herein have been presented in the context of biological end-use applications. It should be understood that luminescent diamonds as disclosed herein can be used in end-use applications other than biological, where the desired improved level of luminescence intensity is useful or beneficial. Other potential uses of luminescent diamonds include, but are not limited to, for magnetic sensors, high-resolution thermal imaging, microscopic sensor arrays, anti-counterfeiting measures, ion concentration monitoring, membrane potential measurement, optical trapping, and strain / pressure sensors. Therefore, it should be understood that luminescent diamonds as disclosed herein are not intended to be limited to a particular end-use application. It should be understood that reference to "one embodiment", "embodiment", "example", etc. of the present disclosure is not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the stated features. For example, any element or feature described with respect to the embodiments herein may be capable of being combined with any element or feature of any other embodiment described herein.

[0022] Therefore, all such modifications and end-use applications of the luminescent diamond are intended to be included within the scope of the present disclosure as defined in the appended claims. In the claims, means-plus-function clauses are intended to cover structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, while a nail and a screw may not be structural equivalents because a nail employs a cylindrical surface to fasten wooden parts together while a screw employs a helical surface, in the context of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to impose any limitation on any claim herein by invoking a means-plus-function requirement unless the claim expressly uses the words 'means for' and the associated function.

Claims

1. A luminescent diamond material, comprising: Diamond particles, the diamond particles comprising: Internal vacancy defects; and Surface quantum dots, The internal vacancy defects and the surface quantum dots produce luminescence in one or a combination of the visible, ultraviolet, infrared or near-infrared spectra.

2. The luminescent diamond material of claim 1, wherein the internal vacancy defect is a nitrogen defect.

3. The luminescent diamond material of claim 2, wherein the nitrogen defects comprise NV defects, NVN defects, N3 optical centres or combinations thereof.

4. The luminescent diamond material of claim 1, wherein the diamond particles exhibit a higher visible luminescence intensity level in one or a combination of the blue, violet-blue, red or green wavelength spectrum than a precursor diamond material used to form the luminescent diamond material.

5. The luminescent diamond material of claim 1, wherein the diamond particles are mechanically interlocked together and combined with a pressure transmitting medium, wherein the luminescent diamond material is made by a high pressure / high temperature process, and wherein the diamond particles comprise diamond grains that have undergone plastic deformation.

6. Luminescent diamond material according to claim 5, wherein the pressure transmitting medium is selected from a material that does not promote intergranular bonding of precursor diamond grains during the high pressure / high temperature process.

7. The luminescent diamond material of claim 5, wherein the pressure transmitting medium is selected from the group consisting of carbonates, nitrates, sulfates, phosphates, chlorates, perchlorates, acetates, chromates, oxalates, sulfides, ammonium compounds, hydroxides, oxides, cyanides, cyanates, dichromates, halides, and combinations or mixtures thereof.

8. The luminescent diamond material of claim 5, wherein the pressure transmitting medium is selected from the group consisting of: a water soluble material, an acid soluble material or an alkali soluble material.

9. The luminescent diamond material of claim 5, wherein the pressure transmitting medium is a chloride.

10. The luminescent diamond material of claim 1, wherein the diamond particles are free of intercrystalline bonded diamond.

11. The luminescent diamond material of claim 1 , wherein the diamond particles exhibit quantum dots only on the surface, and wherein the internal vacancy defects are dispersed throughout the diamond particles and on the surface.

12. The luminescent diamond material of claim 1, comprising greater than 20 volume % diamond and greater than 5 volume % pressure transmission medium, based on the total volume of the luminescent diamond material.

13. The luminescent diamond material of claim 1, comprising greater than 50 volume % diamond and greater than 10 volume % pressure transmission medium, based on the total volume of the luminescent diamond material.

14. The luminescent diamond material of claim 1 comprising a total graphite content of less than 15 wt%, less than 10 wt% or less than 5 wt% without further processing after being produced by a high pressure / high temperature process.

15. A method for making a luminescent diamond, comprising: subjecting a volume of precursor diamond grains to high pressure / temperature conditions at an elevated temperature greater than 900° C. in the presence of a pressure transmitting medium and thereby causing the diamond grains to undergo plastic deformation to produce internal vacancy defects in the diamond grains; subjecting the plastically deformed diamond grains to laser pulses and thereby forming quantum dots on surfaces of the diamond grains, The resulting diamond material exhibits a luminescence intensity level in one or a combination of the visible, ultraviolet, infrared or near infrared spectra that is higher than the luminescence intensity level of the precursor diamond grains.

16. A method according to claim 15, wherein the resulting diamond material is free of intercrystalline bonded diamond.

17. The method of claim 15, wherein the internal vacancy defect is one or more of a nitrogen vacancy defect or a silicon vacancy defect.

18. The method of claim 15, wherein subjecting the plastically deformed diamond grains to laser pulses comprises placing the plastically deformed diamond grains in a liquid.

19. The method of claim 15, wherein the laser pulses are femtosecond laser pulses.

20. The method of claim 15, wherein the pressure transmitting medium is selected from materials that do not promote intercrystalline diamond bonding during the high pressure / high temperature conditions and includes one or more of the following: carbonates, nitrates, sulfates, phosphates, chlorates, perchlorates, acetates, chromates, oxalates, sulfides, ammonium compounds, hydroxides, oxides, cyanides, cyanates, dichromates, halides, or combinations thereof.

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