Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/87—Investigating jewels

Definitions

• the present invention relates to a method of and apparatus for testing whether a natural diamond has had a layer of synthetic diamond deposited thereon. This is of particular importance in testing whether the diamond is wholly natural or whether any part of it comprises CVD diamond material and al ⁇ o in locating such material if present.
• Synthetic diamond material may be deposited on an uncut or part processed natural diamond which is then worked, for example, into a round brilliant cut.
• the synthetic diamond material coating may be deposited onto a fully fashioned brilliant stone after working of the stone.
• the thickness of the synthetic diamond material layer may be very thin (it could be in the range from 5 microns to 10 microns) but the present invention may also be used to detect thicker layers.
• the value of a diamond is in part dependent upon its weight. Accordingly, synthetic diamond material may be deposited onto natural gem diamonds, before or after cutting of the diamond, to increase the weight of the finished product. However, the value of a diamond also reside ⁇ in its qualities of authenticity and uniqueness and in the fact that it is an entirely natural (i.e. mined) product. Thus, a diamond that has not been enlarged by deposition of ⁇ ynthetic diamond material has a value over a diamond which has.
• CVD chemical vapour deposition
• CVD diamond material a low pressure technique involving deposition of synthetic diamond (referred to as CVD diamond material in this specification) onto a substrate from a gas.
• CVD is the most likely way in which synthetic diamond will be deposited on a diamond, although alternative techniques such as physical vapour deposition have been proposed.
• a diamond artificially enlarged by deposition of CVD or similar diamond material is referred to in this specification as a "CVD/natural diamond doublet".
• CVD diamond material may be deposited on a non-diamond or diamond substrate. In the latter case, the CVD diamond material can replicate the structure of the diamond substrate (referred to as "homoepitaxial growth").
• the CVD/natural diamond doublet produced can be identical in appearance, density and other common physical properties to an entirely natural stone and there may be a problem in identifying such a CVD/natural diamond doublet.
• the apparatus should be simple and may be put into operation by a person with relatively little training.
• the method and apparatus should be capable of being operated reliably and consi ⁇ tently by a practised jeweller who has no training in laboratory gemological analysis.
• the method and apparatus should be ⁇ uitable for screening large number ⁇ of stones, one at a time, and should be ⁇ uitable for automation.
• the whole diamond is irradiated and the pattern observed by eye through magnifying means or on a screen via a CCD camera.
• the pre ⁇ ent invention provide ⁇ a method of te ⁇ ting whether a diamond has had a layer of ⁇ ynthetic diamond deposited thereon, comprising observing a plurality of zones of the surface of the diamond, each zone being ob ⁇ erved by irradiating the zone with high energy radiation to excite or ⁇ timulate emi ⁇ ion of luminescence and as ⁇ e ⁇ ing the inten ⁇ ity of the luminescence.
• the pre ⁇ ent invention further provide ⁇ an apparatu ⁇ for te ⁇ ting whether a diamond has a layer of synthetic diamond depo ⁇ ited thereon, compri ⁇ ing a mounting mean ⁇ , a support for a diamond, movably mounted on the mounting means, means for irradiating a diamond supported in the support with high energy radiation to excite or stimulate emi ⁇ ion of lumine ⁇ cence, and mean ⁇ for providing a signal dependent upon the intensity of lumine ⁇ cence produced when a diamond mounted on the ⁇ upport is irradiated.
• Means for driving the support with re ⁇ pect to the mounting mean ⁇ may be provided.
• the mounting mean ⁇ may be fixed with re ⁇ pect to the irradiating means.
• the invention further provide ⁇ an apparatu ⁇ for te ⁇ ting whether a diamond ha ⁇ had a layer of synthetic diamond deposited thereon, comprising an integrating enclosure having a support for a diamond, means for irradiating a zone of a diamond mounted on the support, and means for giving a signal dependent upon the flux intensity of luminescence m the integrating enclosure, produced when a diamond in the integrating enclosure is irradiated.
• the support for the diamond may be movable with respect to the integrating enclosure and may be driven by drive means.
• luminescence is meant emitted radiation of a wavelength generally different to the irradiating radiation which causes it.
• the luminescence intensity is preferably measured.
• a signal dependent upon the intensity of luminescence from each zone is produced.
• the surface of the diamond may be scanned by a beam of irradiating radiation, any significant change m intensity of luminescence between one zone and the next being detected.
• the diamond may be irradiated with ultraviolet radiation of suitable wavelength. Substantially all natural diamonds will luminesce if irradiated with radiation of wavelength less than 225 nm. It is accordingly preferable to use radiation of wavelength le ⁇ than or approximately equal to 225 nm.
• the irradiating radiation may be substantially monochromatic or it may comprise a range or a ⁇ et of wavelength ⁇ .
• This is becau ⁇ e layers of synthetic diamond material may be relatively thin. f the irradiating radiation penetrates to a depth significantly greater than the thickness of the thin layer of ⁇ ynthetic diamond material, lumine ⁇ cence could be produced from underlying natural diamond material which would confuse or swamp out the lumine ⁇ cence from the ⁇ ynthetic diamond layer.
• the diamond is irradiated with radiation of wavelength less than or approximately equal to 225 nm which is very ⁇ trongly absorbed by all types of diamond. This i ⁇ de ⁇ cribed in more detail in British patent application number 9404309.8.
• the irradiating radiation may include radiation of wavelengths greater than 225 nm. Certain radiation band ⁇ of wavelength greater than 225 nm have different absorption characteri ⁇ tics in different types of diamond. Accordingly, such radiation could penetrate the layer theoretically being studied and cause luminescence in other areas of the diamond, which could confuse the results. Irradiating radiation of wavelength much greater than 225 nm may be confused with luminescing radiation. It is desirable that radiation of wavelength greater than 225 nm should be sufficiently low in intensity that lumine ⁇ cence from parts of the diamond apart from the zone of interest does not swamp out or reduce the contrast in observations of lumine ⁇ cence. Preferably at lea ⁇ t 50% of the irradiation energy i ⁇ at wavelength ⁇ le ⁇ s than 225nm. Preferably, however, radiation of wavelengths greater than 225 nm should be ⁇ ub ⁇ tantially excluded by a suitable filter.
• the diamond may alternatively be irradiated with a beam of electrons of suitable energy, but the apparatus would then be complicated.
• the irradiating radiation must be of intensity sufficient to generate observable lumine ⁇ cence.
• the irradiating radiation may be generated by any suitable means, for example a la ⁇ er or other ⁇ ource.
• the irradiating radiation may be directed onto the gem ⁇ tone by any suitable means.
• the attenuation of short wavelength ultraviolet radiation by normal optics is high and it is preferred to use optical equipment which has a high tran ⁇ mis ⁇ ivity at short ultraviolet wavelengths.
• Radiation of wavelengths shorter than 180 nm is attenuated by normal ON optics and by oxygen in air and is effectively filtered out by the apparatus.
• the radiation is focu ⁇ ed onto the diamond. More preferably, the radiation is focused onto an area of the diamond which is ⁇ maller than the total pre ⁇ ented ⁇ urface area of the diamond. Mo ⁇ t preferably the radiation i ⁇ focused to a small spot and scanned over the surface of the diamond.
• the lumine ⁇ cence band ⁇ ob ⁇ erved for various types of diamond fall within a wide range of wavelengths, generally in the visible part of the ⁇ pectrum.
• a signal dependent upon intensity of luminescence falling in a relatively narrow band or a relatively wide band may be given. In the latter case, it is preferable to provide a cut-off filter to exclude the irradiating radiation.
• a synthetic diamond layer depo ⁇ ited upon a natural diamond may be identifiable if the lumine ⁇ cence thereof i ⁇ a different colour to the lumine ⁇ cence of the natural part of the diamond or, more importantly, of a different inten ⁇ ity to the lumine ⁇ cence of the natural part of the diamond. Accordingly, when the plurality of zone ⁇ are te ⁇ ted, ⁇ ignificant differences (for example, the lower signal being of the order of 80%, preferably 50%, or les ⁇ of the higher), in the intensity of luminescence produced by different zone ⁇ of the diamond will ⁇ ugge ⁇ t a CVD/natural diamond doublet. It i ⁇ po ⁇ ible that difference ⁇ in luminescence intensity do not originate in a layer of synthetic diamond.
• the present invention provides a useful guide. However, further testing may be beneficial.
• the intensity of radiation may, in the method of the invention, be assessed by eye.
• means should be provided for exluding the hazardous ultraviolet radiation from the observer. If the luminescence is as ⁇ e ⁇ ed by eye, it is not necessary to form an image of the zone irradiated if the irradiating radiation can be confined to the zone of interest and irradiation of other zones avoided. In that case, the luminescence, rather than the diamond will be observed in effect.
• the observed radiation comprises no irradiating radiation.
• a small amount of irradiating radiation may be tolerated in the ob ⁇ erved radiation if it doe ⁇ not ⁇ wamp out luminescence.
• the luminesced radiation may be detected by any suitable mean ⁇ .
• a beam splitter may be placed in the path of the irradiating radiation, being configured to direct luminesced radiation from the diamond to a detector.
• a filter for filtering out irradiating radiation may be provided for the detector.
• the diamond may be placed in an integrating enclo ⁇ ure and a zone of the diamond irradiated with irradiating radiation.
• the integrating enclo ⁇ ure i ⁇ provided with a detector for giving a signal dependent upon the intensity of lumine ⁇ cence in the integrating enclosure produced when the given zone is irradiated.
• the detector may include a filter for filtering out irradiating radiation.
• the integrating enclosure comprise ⁇ an integrating ⁇ phere.
• the zone of the diamond of intere ⁇ t must be irradiated and ⁇ ub ⁇ tantially no other zone ⁇ .
• the diamond may be irradiated using a beam of confined dimension ⁇ which may be produced, for example, by an aperture between the diamond and the radiation ⁇ ource.
• a single zone of the diamond is irradiated at any one time and a plurality of such zones are irradiated sequentially.
• a plurality of different zones of the diamond may be independently irradiated simultaneou ⁇ ly and signals dependent upon the intensity of lumine ⁇ cence produced by each re ⁇ pective zone provided, in ⁇ ucce ⁇ sion or simultaneously, the observations being subsequently compared.
• the diamond may be placed with the zone of interest in contact with the aperture, to reduce the inclusion of light from other parts of the diamond. This arrangement is particularly suitable if a beam splitter is provided in the irradiation path for passing luminescence to a detector.
• the confined beam may be of variable dimension or of fixed dimension. It may correspond in ⁇ ize to a facet of a worked diamond or to a part of a facet. Preferably, the confined beam i ⁇ smaller than the maximum dimension of the diamond, or is adjustable in size to allow this.
• the aperture may be of size 1 - 15 mm acros ⁇ , preferably 5 - 10 mm. An iris aperture may be provided, adjustable in size for best results.
• the beam may be focus ⁇ ed to a ⁇ mall ⁇ pot of ⁇ ize 1 micron - 1 mm across, preferably 5 - 100 microns, and preferably scanned acros ⁇ the diamond.
• Radiation emanating from the diamond may be pas ⁇ ed to the detector through a filter.
• the filter is a cut-off filter for filtering out the irradiating radiation.
• a further filter may be provided for passing selected luminescence bands. For example, a number of interchangeable filters could be used, each pa ⁇ ing light of a different wavelength.
• the beam is preferably scanned (ie moved continuou ⁇ ly or semi continuously) over the surface of the diamond.
• Means for scanning the beam may be provided in the form of means for moving the beam with respect to the diamond.
• the diamond may be rotated about an axis not coincident with the beam of radiation.
• the axis is normal to the beam of radiation.
• Means may be provided for moving the diamond linearly with respect to the beam of radiation, for example in two directions normal to the beam of radiation.
• Means may be provided for giving a signal if the intensity of radiation emitted by the diamond changes by an amount exceeding a predetermined value. This is particularly useful if the diamond i ⁇ scanned continuously. It allows changes in surface composition to be readily identified.
• the signal giving means may co pri ⁇ e mean ⁇ for giving a ⁇ ignal dependent upon inten ⁇ ity of radiation and ⁇ ignal generating means for giving a change signal if the intensity of radiation changes by a given amount.
• the change signal may be given if the inten ⁇ ity of radiation measured change ⁇ by 5%, preferably by more than 10%, preferably by greater than 20%.
• the ⁇ ignal generating mean ⁇ may compri ⁇ e a timer ⁇ o that a change ⁇ ignal is only given if the intensity of radiation changes by a predetermined amount within a predetermined period of time. Means may be provided for altering the period of time and/or the amount by which the signal must change before a ⁇ ignal is given.
• the diamond is placed in a rotatable mount and rotated continuou ⁇ ly, whil ⁇ t the intensity of lumine ⁇ cence i ⁇ measured.
• a noisy or modulated DC ⁇ ignal variants in intensity of lumine ⁇ cence being cau ⁇ ed by naturally occurring slight local differences in diamond compo ⁇ ition, and internal reflection and refraction
• a much broader pul ⁇ e of higher or lower inten ⁇ ity will suggest a CVD/natural diamond doublet.
• the diamond i ⁇ rotated a plurality of times in order to give a plurality of readings which may be combined stati ⁇ tically to give a ⁇ tatistically improved reading.
• the invention is preferably used with fluorescence - that is, luminescence produced effectively instantaneously by a zone of a diamond when it is irradiated with an electron beam or high energy ultraviolet radiation.
• the apparatus of the invention is preferably confined in a light-tight box. Thi ⁇ i ⁇ to exclude radiation from external sources from reaching the detector and to prevent the potentially harmful high energy ultraviolet radiation escaping and causing damage to skin and eyes.
• Figure 1 i ⁇ a ⁇ chematic illu ⁇ tration of apparatu ⁇ for carrying out the invention, according to a first embodiment
• Figure 2 is a schematic illu ⁇ tration of apparatus for carrying out the invention according to a second embodiment
• Figure 3 show ⁇ a diagram of the signal output obtained.
• a diamond 2 i ⁇ mounted in or on a mounting 3 which i ⁇ rotatable and which i ⁇ tran ⁇ parent to ⁇ hortwave ultraviolet light and to visible light.
• the diamond is irradiated with ultraviolet radiation of wavelength les ⁇ than 225 nm.
• the radiation i ⁇ generated by a ⁇ ource 4 ( ⁇ uch a ⁇ a Xenon fla ⁇ h lamp, deuterium lamp or ultraviolet la ⁇ er).
• Irradiating radiation i ⁇ filtered through a cut-off filter 5 which remove ⁇ visible radiation, in order to improve the contra ⁇ t of the luminescence observed. Radiation is focu ⁇ ed onto a small zone of the diamond by a lens 6.
• the small zone of the diamond will be caused to luminesce, generating luminescence of intensity and colour dependent upon the local composition of the zone irradiated. Some of this luminescence passes ⁇ back down the direction of irradiation to beam ⁇ plitter 7 which pa ⁇ e ⁇ lumine ⁇ cence through a lens sy ⁇ tem 8 having a filter 9 for removing radiation of wavelength les ⁇ than 225 nm, the luminescence being focused onto a photomultiplier tube 10.
• the photomultiplier tube 10 i ⁇ connected to a proce ⁇ or 11 and monitor 12 to di ⁇ play a ⁇ ignal dependent upon the lumine ⁇ cence produced.
• a plurality of zones of the diamond are irradiated by fixing the diamond with respect to rotatable mount 3 and rotating the mount (and the diamond) with respect to the rest of the apparatus ⁇ o that the point of contact of the radiation move ⁇ over the ⁇ urface of the diamond.
• the mount i ⁇ al ⁇ o movable in a direction normal to the beam and to the axis of rotation so that the full height of the stone can be scanned by repeated rotations.
• the diamond 2 shown in Figure 1 is a CVD/diamond doublet, with a layer of CVD synthetic diamond material on the table of the diamond.
• the signal from the photomultiplier tube 10 displayed on monitor 12 a ⁇ the diamond 2 is rotated will be a "noisy DC" signal as the irradiating radiation pas ⁇ es over the natural part of the ⁇ tone, followed by a relatively broad dip to a lower (or higher) noi ⁇ y DC ⁇ ignal as the focus of the irradiating radiation moves over the synthetic part of the stone, cau ⁇ ing luminescence of a different intensity.
• the "noise” will be due to small local variations in diamond composition, external and internal reflection and refraction etc.
• the apparatus of Figure 1 is not intended to detect the colour of the luminescence, though it may be modified to do so by providing a number of exchangeable coloured filters in front of the detector.
• the optic ⁇ used in Figure 1 are UN tran ⁇ mitting optic ⁇ such as those manufactured by Spindler & Hoyer.
• FIG. 2 shows a schematic apparatus for carrying out a method according to a second embodiment of the invention.
• a diamond 13 which i ⁇ a CVD/natural diamond doublet, is mounted on a rotatable mount similar to the mount 3 shown in Figure 1.
• the mount and the diamond are placed inside an integrating sphere 15 which is lined with a material with good reflectance in the visible range.
• the diamond is irradiated using a UN source 16.
• Light from the source is passed through a filter 17 to remove light of wavelengths greater than 225nm and is focused by a lens 18 onto the surface or near the ⁇ urface of the diamond 13.
• the irradiating radiation i ⁇ of wavelength le ⁇ than 225 nm and therefore causes luminescence.
• a filter 20 i ⁇ provided for filtering out the irradiating radiation and a baffle 21 i ⁇ provided in the integrating ⁇ phere 15 to ensure that the radiation passing to the photomultiplier tube 19 is representative of the luminous flux den ⁇ ity in the ⁇ phere.
• a processor 22 and monitor 23 is provided for ⁇ howing the ⁇ ignal produced by the photomultiplier tube 19.
• the signal produced by the photomultiplier tube 19 when the mount 14 and diamond 13 are rotated is similar to that shown by the monitor in Figure 1.
• Figure 3 show ⁇ in more detail a signal produced by the photomultiplier tube 19 or 10 of Figure 2 or 1 respectively.
• Fluctuation ⁇ in the ⁇ ignal (“noise") due to natural variations in the diamond are distinct from change ⁇ in the ⁇ ignal due to layer ⁇ of synthetic diamond in that fluctuations are lower in intensity and extend over smaller ranges of angles of rotation.
• the proce ⁇ or 22 or 11 may be programmed to mea ⁇ ure the rate of change of the ⁇ ignal received from the photomultiplier tube 19 or 10.
• the proce ⁇ or 11 or 22 may be connected to mean ⁇ for rotating the mount 3 or 14 re ⁇ pectively.
• the rate of change of the ⁇ ignal with re ⁇ pect to time or with respect to position of the mount 3 or 14 may be mea ⁇ ured.
• the proce ⁇ ing means 11 or 22 may be programmed to give a signal if the rate of change of the signal from the photomultiplier tube 10 or 19 exceeds a given value.
• a signal is then given, for example on monitor 12 or 23 to indicate that a "jump" in the emission of the diamond had been detected.
• Such a "jump" in emi ⁇ ion can be correlated with the pre ⁇ ence of a synthetic diamond layer.

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• General Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Luminescent Compositions (AREA)

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• 1995
  • 1995-07-24 GB GB9515143A patent/GB2303698A/en not_active Withdrawn
• 1996
  • 1996-07-22 JP JP9506452A patent/JPH11509629A/ja active Pending
  • 1996-07-22 KR KR1019980700497A patent/KR19990035837A/ko not_active Application Discontinuation
  • 1996-07-22 CN CN96196962A patent/CN1196120A/zh active Pending
  • 1996-07-22 AU AU65271/96A patent/AU702792B2/en not_active Ceased
  • 1996-07-22 CA CA002227472A patent/CA2227472A1/en not_active Abandoned
  • 1996-07-22 WO PCT/GB1996/001751 patent/WO1997004302A1/en not_active Application Discontinuation
  • 1996-07-22 RU RU98103246/28A patent/RU2175125C2/ru not_active IP Right Cessation
  • 1996-07-22 EP EP96925014A patent/EP0840890A1/en not_active Withdrawn
  • 1996-07-22 EP EP01117365A patent/EP1158293A3/en not_active Withdrawn
  • 1996-07-23 ZA ZA9606245A patent/ZA966245B/xx unknown
  • 1996-07-23 IL IL11892296A patent/IL118922A/xx not_active IP Right Cessation
  • 1996-08-07 TW TW088202318U patent/TW433463U/zh unknown
• 2002
  • 2002-01-21 HK HK02100462.7A patent/HK1041047A1/zh unknown

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