Coloured diamond

a technology of coloured diamonds and diamonds, applied in the direction of condensed vapor transportation, crystal growth process, transportation and packaging, etc., can solve the problems of limited colours and uniformity that can be produced, and the method is not readily applicable to brown single crystal cvd diamonds, etc., to increase the purity of colour, increase the lightness, remove, reduce or modify the effect of absorption

Inactive Publication Date: 2007-04-12
TWITCHEN DANIEL JAMES +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0029] The coloured CVD diamond crystal of the invention preferably has a desirable hue. The hue angle for a particular hue can be found by extending the line back from the point representing that hue on the a*b* colour plot as described more fully hereinafter, and shown on FIG. 4. The hue angle of the CVD diamond after heat treatment will typically be less than 65° or less than 60° or less than 55° or less than 50°. It is well known that pink diamonds are much admired and highly prized by jewellers, collectors and consumers because of their universally acknowledged great beauty and rarity (Pink Diamonds, John M. King et al., Gems and Gemology, Summer 2002). In the diamond industry green diamonds are also highly valued and greatly admired (Collecting and Classifying Coloured Diamonds, Stephen C. Hofer, 1998, Ashland Press Inc. New York). In general, pink and green diamonds are more prized the purer the colour and the weaker the influence of secondary colour modifiers. Heat treatment or annealing conditions of the invention can increase the purity of the colour by increasing, removing, reducing or modifying absorption that contributes to colour modification. At the same time, annealing or heat treatment can increase the lightness by reducing the concentration of defects that reduce absorption over wide regions of the spectrum.

Problems solved by technology

However, there are limitations to the colours and uniformity that can be produced as a consequence of competitive defect formation and because of the strong growth sector dependence associated with the concentration of defects such as nitrogen in diamond.
This method is therefore not readily applicable to brown single crystal CVD diamond.

Method used

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Examples

Experimental program
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Effect test

example 1

[0107] A 3.2 mm thick CVD layer was grown on an HPHT synthetic diamond substrate. The surface of the substrate on which growth was to take place was prepared according to the method described in WO 01 / 96634.

[0108] This substrate was mounted on a tungsten substrate using a high temperature braze suitable for diamond. This was introduced into a microwave reactor, an etch and growth cycle used to prepare the substrate surface, and then growth commenced. More particularly: [0109] 1) The reactor was pre-fitted with point of use purifiers, reducing nitrogen levels in the incoming gas stream (excluding the N2 dopant line) to below 80 ppb, as determined by the modified GC method described above. [0110] 2) An in situ oxygen plasma etch was performed using 30 / 150 / 1200 sccm (standard cubic centimetre per second) of O2 / Ar / H2 at 235×102 Pa and a substrate temperature of 840° C. [0111] 3) This moved without interruption into a hydrogen etch at 850° C. with the removal of the O2 from the gas flow...

example 2

[0118] A 3.1 mm thick CVD layer was grown on an HPHT synthetic diamond substrate using a process similar to that set out in Example 1. The single substitutional nitrogen concentration in this sample was estimated to be approximately 0.5 ppm from the strength of the 270 nm feature in the absorption spectrum.

[0119] The layer was polished into a round brilliant of 0.49 carats that was graded as light brown, VS1. It was then annealed at 2100° C. for twenty-four hours under diamond stabilising pressure of approximately 7.5×109 Pa (75 kbar). After repolishing to 0.44 carats, it was then graded as fancy light greyish green, VS1.

[0120] The culet of the round brilliant was then enlarged to allow an absorption spectrum to be recorded. By itself, the absorption spectrum was insufficient to explain the green hue of the stone. Photoluminescence spectra (with a HeCd laser or Xe lamp excitation) showed strong green luminescence from defects (H3 and other unidentified defects) that were formed by...

example 3

[0121] A 3.10 mm thick CVD layer was grown on an HPHT synthetic diamond substrate in a process similar to that set out in Example 1. The single substitutional nitrogen concentration in this sample was estimated to be approximately 0.5 ppm from the strength of the 270 nm feature in the absorption spectrum. The absorption spectrum also contained broad bands centred at approximately 360 nm and 515 nm and a general rise (ramp) in absorption coefficient from the red to the ultra-violet.

[0122] The layer was polished into a round brilliant of 0.51 carats that was graded as light brown, I3. It was then annealed at 1700° C. for twenty-four hours under diamond stabilising pressure of approximately 6.5×109 Pa (65 kbar). Without any further processing it was graded as light orangish pink, I3.

[0123] The culet of the round brilliant was then enlarged to allow an absorption spectrum to be recorded. This indicated no significant change in concentration of single substitutional nitrogen. The stren...

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Abstract

A method of producing a single crystal CVD diamond of a desired colour which includes the steps of providing single crystal CVD diamond which is coloured and heat treating the diamond under conditions suitable to produce the desired colour. Colours which may be produced are, for example, in the pink-green range.

Description

[0001] This is a continuation application of U.S. application Ser. No. 10 / 655,040, filed Sep. 5, 2003.BACKGROUND OF THE INVENTION [0002] This invention relates to a method of producing coloured diamond and more particularly coloured single crystal chemical vapour deposition (hereinafter referred to as CVD) diamond that is suitable, for example, for ornamental purposes. [0003] Intrinsic diamond has an indirect band gap of 5.5 eV and is transparent in the visible part of the spectrum. Introducing defects or colour centres, as they will be called hereinafter, which have associated energy levels within the band gap gives the diamond a characteristic colour that is dependent on the type and concentration of the colour centres. This colour can result from either absorption or photoluminescence or some combination of these two. One example of a common colour centre present in synthetic diamond is nitrogen which, when on a substitutional lattice site in the neutral charge state, has an asso...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C30B23/00C30B25/00C30B28/12C30B28/14C01B31/06C30B29/04C30B33/00
CPCC30B29/04C30B33/00Y10T428/2982C30B33/02C01B32/28
Inventor TWITCHEN, DANIEL JAMESMARTINEAU, PHILIP MAURICESCARSBROOK, GEOFFREY ALAN
Owner TWITCHEN DANIEL JAMES
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