JP2571797B2 - Blue-green diamond and method for producing the same - Google Patents

Description

The present invention relates to a blue-green diamond and a method for producing the same,
In particular, the present invention relates to a blue-green diamond suitable for use in decorative applications and a method for producing the same.

[Prior Art] Conventionally, blue-green colored diamonds have been produced by irradiating a natural rough with an electron beam.

The cause of the blue-green coloration is that a lattice defect is formed in the crystal by electron beam irradiation, and this defect causes the absorption wavelength to be 550 nm to 7 nm.
This is because the 40nm GR1 color center is created. For details on the fabrication method and optical characteristics of this color center, refer to Diammond Research (1) by CDCLARK and J. WALKER.
972), pp. 2-5.

In the case of coloring blue-green, not only the conditions for producing the GR1 center by electron beam irradiation, but also the color of the base of the rough stone are important. In the case of natural gemstones, there are gemstones of various colors, from colorless and transparent gemstones to pale yellow, yellow, brown and brown. In order to color blue-green, it is necessary to use a colorless transparent or pale yellow raw stone among the above-mentioned raw stones. With other rough stones, the rough stone itself becomes darker and blue-green cannot be obtained. It is the N3 center found in most natural roughs that makes the rough yellow. N3 Center is 3
This is the color center formed when the nitrogen atoms are aggregated, and its absorption is around 400 nm. The absorption near this is purple, and the complementary yellow color enters the human eye. Since this wavelength range is close to the human visual limit wavelength (380 nm), N3
When the center is small, it looks almost transparent, and when it is large, it looks pale yellow. ATCollin
s New Diammond, Vol. 3, No. 2 (translated by Yoichiro Sato) has a detailed description.

In addition, as a diamond exhibiting a blue color, there is a IIa type diamond containing boron in a crystal. But,
This is distinctly different in tone from the blue-green diamond according to the present invention and is not included in the scope of the present invention.

[Problems to be Solved by the Invention] The conventional blue-green diamond has the following disadvantages.

i) When heated to 600 ° C., yellow color increases and discoloration occurs.

ii) When exposed to sunlight, it emits blue fluorescent light (luminescence) and changes its color.

The cause of i) is that there are many nitrogen atoms in natural diamond. Lattice defects created by electron beam irradiation combine with these nitrogen atoms by heating to form a new color center. These color centers are called H3, H4, NV centers, which cause the crystals to exhibit yellow and reddish colors. Regarding the production method and optical characteristics of each color center,
ports on Progress in Physics, John Walker, Chapter 42
Volume (1979).

The cause of ii) is the N3 center present in most crystals in natural rough. Since the absorption at the N3 center is near 400 nm, which is close to the visual limit wavelength, it looks transparent even if it exists a little. However, N3 center is strong blue (400-470nm)
The diamond emits blue light when exposed to sunlight, causing it to turn blue.

An object of the present invention is to provide a blue-green diamond having a stable color tone which does not discolor even when heated to 600 ° C. or more and exposed to sunlight.

[Means for Solving the Problems] The blue-green diamond according to the present invention has an absorption coefficient at 650 nm of the GR1 center in the crystal of 0.3 to 8 cm ⁻¹ ,
Absorption coefficient due to other absorption within the wavelength range of 80 nm to 780 nm
0.2 cm ^-1 or less, and the Ib type nitrogen content in the crystal is 5 × 10
It is characterized by being ¹⁷ atoms / cm ³ or less.

The method for producing a blue-green diamond according to the present invention includes the following steps.

An artificially synthesized diamond crystal having a content of Ib type nitrogen in the crystal of 5 × 10 ¹⁷ atoms / cm ³ or less, 2-4 MeV
Irradiating an electron beam with an acceleration voltage of 5 × 10 ¹⁶ to 2 × 10 ¹⁸ electrons / cm ² .

Then, annealing at 550 to 600 ° C. for 30 minutes or more under a vacuum of 10 Torr or less.

[Explanation of Means] (I) Blue-green diamond (1) Nitrogen content: When natural gemstones are used as in the conventional method, when heated to 600 ° C, yellow or reddish color increases and discoloration occurs. Further, there has been a problem that when exposed to sunlight, blue fluorescent light is emitted and discolored. This is due to the large amount of nitrogen present in natural diamond. In addition, among natural gemstones, those having a very low nitrogen content are directly used as decorative diamonds, and are too expensive to be industrially processed and used, so that it is difficult to put them into practical use.

In the present invention, the problem has been solved by using artificial synthetic diamond containing almost no nitrogen. Specifically, if the nitrogen content is 5 × 10 ¹⁷ atoms / cm ³ or less,
Even if heated to 600 ° C., a yellow or red color center (NV center) is hardly formed, and the diamond does not change color. Such a diamond having a low nitrogen content can be produced by a known method using a getter such as Ti, Al, Zr, and Hf. Also, in artificial synthetic diamond
The problem of the absence of the N3 center and the emission of blue fluorescence is resolved. However, in the case of artificially synthesized diamond, as the nitrogen content increases, an S3 center with absorption near 500 nm is formed. For this reason, there is a new problem that when exposed to strong light, yellow-green fluorescence is emitted and the color changes. But,
This fluorescence is not so intense and is not a problem when the nitrogen content is 1.7 × 10 ¹⁹ atoms / cm ³ or less. Therefore, when the nitrogen content is 5 × 10 ¹⁷ atoms / cm ³ or less as in the present invention, the discoloration due to the fluorescence does not cause any problem.

Even if it is a natural gemstone, it contains almost no nitrogen in the crystal
Diamonds called type IIa are rarely produced, but the proportion is less than 1%. Therefore, it is extremely difficult to supply a large amount of blue-green diamond using this rough. Also, natural IIa type rough is more than 10 times more expensive than colored diamond, so that blue-green diamond using this rough cannot be supplied practically.

(2) Regarding the absorption coefficient: One of the greatest features of the present invention is that the absorption coefficient of the GR1 center is found to be correlated with the decorative value, and the optimal value of the absorption coefficient is set to the range of 0.3 to 8 cm ^-1 . It is in the point which did. If the absorption coefficient of the GR1 center is less than 0.3 cm ^-1, it will not show bluish green. On the other hand, when it exceeds 8 cm ⁻¹ , the crystal loses its transparency and has no decorative value.

Another feature of the present invention is that it has been found that other absorption based on H2 center or the like reduces the transparency of the color of the crystal, and the optimum value of the absorption coefficient is set to 0.2 cm ^-1 or less. It is in. When this value is 0.2 cm ^-1 or less, it has no effect on the crystal clearness.

(II) Manufacturing Method Another major feature of the present invention is that blue-green diamond can be manufactured by a special manufacturing method.

(1) Regarding artificial synthetic diamond: This requirement is as described in the above item (I) (1).

(2) Regarding electron beam irradiation: The electron beam irradiation is performed at an accelerating voltage of 2 to 4 MeV and 5 × 10 ¹⁶ to 2
It is performed under the condition of × 10 ¹⁸ electrons / cm ² . If the acceleration voltage in electron beam irradiation is less than 2 MeV, the GR1 color center cannot be formed uniformly in the crystal. Above 4 MeV, there is a possibility of activation. If the irradiation dose is less than 5 × 10 ¹⁶
A GR1 center with an absorption coefficient of 0.3 cm ^-1 or more cannot be manufactured. If it exceeds 2 × 10 ¹⁸ electrons / cm ² , the absorption coefficient becomes 8c
exceeds m ^-1 .

(3) Annealing: Annealing is performed at 550-600 ° C under a vacuum of 10 Torr or less.
Perform for 30 minutes or more.

By annealing at 550-600 ° C for 30 minutes, GR
Absorption at other than one center can be reduced sufficiently. Five
Below 50 ° C., other absorptions cannot be reduced sufficiently. Above 600 ° C, the GR1 center begins to decrease rapidly. Annealing for less than 30 minutes makes it difficult to reduce other absorptions sufficiently. When annealing is performed in an atmosphere exceeding 10 Torr, the diamond surface may be graphitized.

Example 1 Six artificially synthesized diamonds (nitrogen content: 2 × 10 ¹⁷ atoms / cm ³ ) synthesized by the temperature difference method were applied to ³ MeV, 1 × 10 ^{16 to} 5 ×.
After irradiating with an electron beam under the condition of 10 ¹⁸ electrons / cm ² , annealing was performed at a temperature of 600 ° C. under a vacuum of 1 Torr for 10 minutes to 1 hour.

The obtained sample was analyzed by an ultraviolet-visible spectrophotometer.
The GR1 center and other absorption coefficients were measured.

Also, the obtained sample was brilliant cut to a size of 0.8 to 1.0 carats / piece. And, to evaluate the value as a decorative application, randomly selected from 18 to 65 years old
We asked 100 women to observe the sample and asked questionnaires for the following items. Table 1 shows the results. In Table 1, the questionnaire results indicate the number of persons who answered "yes".

Is there a sense of transparency? Is it a vivid color? Is it decorative? Example 2 Two artificial synthetic diamonds (nitrogen content: 5 × 10 ¹⁷ to 1 × 10 ¹⁸ atoms / cm ³ ) and three natural diamonds (nitrogen content: 2.2 × 10 ¹⁹ to 3.4 × 10 ²⁰
Atomic atoms / cm ³ ) were irradiated with an electron beam under the conditions of ² MeV, 7 × 10 ¹⁷ electrons / cm ² . After that, only artificial synthetic diamond, 10 Torr
Annealing was performed at 600 ° C. for 30 minutes under a vacuum of.

The obtained sample was analyzed by an ultraviolet-visible spectrophotometer.
The absorption coefficient was measured by GR1 center and other absorption.

Thereafter, each sample was exposed to sunlight to determine whether it emitted blue fluorescence. After heating at 600 ° C. for 10 minutes, it was examined whether discoloration occurred. Table 2 shows the results.

Example 3 Four synthetic diamonds (nitrogen content: 3 × 10 ¹⁷ atoms / cm ³ ) synthesized by a temperature difference method were applied to 4 MeV, 1 × 10 ¹⁸ electrons / c.
After performing electron beam irradiation under the condition of m ² , annealing treatment was performed at 500 to 650 ° C. for 30 minutes under a vacuum of 10 Torr.

The obtained sample was analyzed by an ultraviolet-visible spectrophotometer.
The absorption coefficient was measured by GR1 center and other absorption.

In addition, the obtained sample was brilliant cut to a size of 0.5 to 0.6 carats / piece. In order to evaluate the value as a decorative use, it was evaluated in the same manner as in Example 1. Table 3 shows the results. The results of the questionnaire in Table 3 indicate the number of people who answered "yes".

[Effects of the Invention] As described above, according to the present invention, a blue-green diamond having a stable color tone that does not discolor even when heated at 600 ° C or exposed to sunlight can be obtained. The diamond according to the present invention is particularly effective when used for decorative applications.

Claims (3)

(57) [Claims] 1. A absorption coefficient in 650nm of GR1 centers in the crystal is 0.3～8Cm ^-1, the absorption coefficient due to other absorbent in the wavelength range of 380nm~780nm is at 0.2 cm ^-1 or less, in the crystal A blue-green diamond having an Ib type nitrogen content of 5 × 10 ¹⁷ atoms / cm ³ or less. 2. The blue-green diamond according to claim 1, wherein the color tone does not change even when heated to 600 ° C., and the color tone does not emit blue fluorescence even when exposed to sunlight. . 3. An artificial synthetic diamond crystal having a content of Ib type nitrogen in the crystal of 5 × 10 ¹⁷ atoms / cm ³ or less,
Irradiating an electron beam with an acceleration voltage of 2 to 4 MeV and 5 × 10 ¹⁶ to 2 × 10 ¹⁸ electrons / cm ² , and thereafter, at 550 to 600 ° C. under a vacuum of 10 Torr or less.
Performing a anneal for 30 minutes or more.