RU204985U1 - Gemstone Identification Device - Google Patents

Abstract

The proposed utility model relates to the field of identification of precious stones, first of all, diamonds. To solve the problem of how to distinguish between natural, synthetic, refined diamonds and polished diamonds. Gemstones suitable for analysis include colorless and colored, cut and rough diamonds. The device described is also suitable for the analysis of other gemstones that give off luminescence when exposed to UV radiation. The technical result is to improve the accuracy of identification of different in nature and origin of precious stones with the possibility of simultaneous analysis of a large number of products based on the photoluminescence pattern under UV excitation. This technical result is achieved by the fact that the device for identifying precious stones includes devices located in a darkened case: a power supply, transmitting a video camera with a lens for transmitting an image to a visual display device, a source of exciting radiation in the form of a group of long-wave UV LEDs with a wavelength of 300 nm to 380 nm and a group of short-wave UV LEDs with a wavelength of 240 nm to 300 nm and a control unit for switching LEDs and adjusting their brightness to ensure the accuracy of identifying gemstones of different nature and origin based on an analysis of the photoluminescence pattern under UV excitation. 8 p.p. f-ly, 1 dwg.

Description

The utility model relates to the field of identification of precious stones, first of all diamonds. It is designed to solve the problem of how to distinguish between natural, synthetic, refined diamonds and polished diamonds. Gemstones suitable for analysis include colorless and colored, cut and rough diamonds. The device described is also suitable for the analysis of other gemstones that give off luminescence when exposed to UV radiation.

Modern gemology of precious stones, especially diamonds, has faced new challenges:

the quality has improved, the size has increased and the cost of synthetic diamonds has decreased. Diamonds from them, officially or unofficially, appeared on the jewelry market;

the technology of upgrading low-grade brown natural crystals using high-temperature annealing has been developed.

As a result, the need for the development of methods and devices operating on their basis for the identification and differentiation of natural, synthetic and refined gem-quality diamonds has increased. The task of determining the origin of a diamond is usually entrusted to the diamond appraiser or gemologist during the preparation of the certification or appraisal certificate. The origin of a diamond is a key factor in its market value and is of paramount importance.

Currently, gem-quality diamonds are produced artificially by two methods: high pressure and high temperature (HPHT) and chemical vapor deposition (VPCO). The impurity and defect composition of these crystals can be very different. Advances in synthesis technology have made it possible to control impurities well, making it possible to grow pure colorless crystals. These crystals are not inferior to the best natural ones. They are transparent to electromagnetic radiation with wavelengths greater than 225 nm and contain a negligible amount of impurities (less than 0.1 ppm nitrogen). The best examples of such diamonds have few defects and are free from internal stresses.

There are many physical characteristics that distinguish natural diamonds from synthetic and refined diamonds. But the wide range of characteristics of both natural and synthetic diamonds makes this task difficult.

The main distinguishing property of crystals of different origins is the composition and concentration of nitrogen and nitrogen-vacancy defects. This difference underlies the generally accepted classification of diamonds: IaA (nitrogen, type A aggregates dominate), IaB (nitrogen, dominate aggregates of type B1 and B2), IIa (low nitrogen), Ib (contain nitrogen in single substitutional positions - C defect), IIb (boron impurity dominates). The main difference between synthetic and refined natural diamonds from purely natural diamonds is the length of time they stay in high temperature conditions. Natural crystals grow and are exposed to relatively low temperatures (<1400 ° C) for millions of years, while the processes of diamond synthesis and / or its thermobaric treatment last hours, maximum hundreds of hours. With such a duration, complete transformation of nitrogen defects is impossible.

The most informative methods of gemological analysis of diamonds are optical methods, such as optical absorption in the UV, visible and IR ranges, Raman scattering, etc. But the most sensitive method is luminescence. Luminescence is the emission of visible (as well as near UV and IR) light that occurs when the action of an excitation source (laser, UV lamp, X-ray tube, electron gun, etc.) pulls out electrons in the volume of a solid from their stable “basic "States and translates into" excited "states. When the electron returns to its normal, ground state, energy is released, often in the form of visible light. For gemological analysis, it is most convenient to use photoluminescence excited by a light source, usually in the UV range. Almost always, the emitted light quanta have less energy in the electromagnetic spectrum (that is, longer wavelengths) than the light from the excitation source. Luminescence is divided into fast (fluorescence) and slow (phosphorescence) according to the emission time.

On the market there are devices of various levels of complexity that allow, with a greater or lesser degree of reliability, to solve the problem of determining the origin and history of a diamond. Many of these devices use diamond photoluminescence.

In mineralogy and gemology, a mercury-quartz lamp, usually of low pressure, is widely used to excite the photoluminescence of crystals. It produces light in a wide range of radiation - from the hard UV to the near-IR ranges. However, its use has several disadvantages:

1.To ignite the discharge in the lamp and for its operation, a high voltage is required, which is inconvenient in portable devices and poses a threat of electric shock to personnel;

2. The efficiency of a mercury-quartz lamp is low. In addition, of the total electromagnetic radiation of the lamp, the UV range accounts for a small part of the energy. To isolate it, you have to use a UV filter;

3. It takes about 1 minute for the lamp to light up. During this time, mercury evaporates into its volume. This reduces the efficiency of the device. After turning off the lamp, it emits light for some time. This makes it difficult to implement the observation of phosphorescence - you have to use a fast-closing shutter;

4. the discharge in the lamp burns unstably, which leads to fluctuations in the excitation intensity;

5.Lamps have a limited lifespan, usually around 1000 hours, especially if they are turned on and off frequently. Environmentally friendly disposal of used lamps is required. International environmental legislation is gradually tightening the requirements for the use of mercury lamps up to their complete ban;

6. The emission spectrum of a low-pressure lamp contains both a continuous component and several narrow lines of mercury (578, 546, 436, 405, 365, 254, 185 nm). To isolate narrow-band radiation (for example, lines at 365 and 254 nm), one has to use expensive narrow-band filters. The selection of narrow bands at other wavelengths (where there are no narrow lines of mercury) gives a very low radiation intensity;

7. operation of the lamp in air leads to the formation of a poisonous gas ozone;

8. It is practically very difficult to electrically control the intensity of the lamp glow within a wide range;

9. the size of the luminous area in the lamp is large, which makes it difficult to focus its radiation.

Meanwhile, in recent years, there has been rapid progress in the field of UV LEDs. It is based on the development and improvement of the technology of semiconductor compounds GaN, AlGaN, InGaN, InAlGaN. GaN-based LEDs with a maximum emission at 365 nm (refers to the UV-A range) are characterized by compact dimensions, low cost, high luminous power, and high efficiency. There is rapid progress in the advancement of UV LEDs to short wavelengths (UV-B and even UV-C ranges) through the use of the AlGaN compound. Such LEDs are becoming more powerful, cheaper, and more efficient.

The closest analogue to the claimed solution is a device for measuring parameters of precious stones RU 2 664 910 C2. It describes all possible options for measuring the optical transmission and photoluminescence of diamonds. LEDs in the UV range from about 300 nm to about 520 nm and various lasers are used as excitation light sources. Radiation is fed to the crystal from below through a bundle of optical fibers tightly pressed against it. Registration of transmitted radiation and photoluminescence is also carried out mainly through optical fibers. In different versions of the device, the spectral composition of light is measured using spectrometers.

The main disadvantage of the device described in patent RU 2 664 910 C2 is the impossibility of regulating a wide range of luminescence intensities of different diamonds, the impossibility of working immediately with a group of stones. In addition, the use of light sources with wavelengths less than 300 nm is not envisaged.

The task to which the stated solution is directed is the elimination of these shortcomings.

The technical result is to improve the accuracy of identification of different in nature and origin of precious stones with the possibility of simultaneous analysis of a large number of products based on the photoluminescence pattern under UV excitation.

This technical result is achieved by the fact that the device for identifying precious stones includes devices located in a darkened case, a power supply, transmitting a video camera with a lens for transmitting an image to a visual display device, a source of exciting radiation in the form of a group of long-wave UV LEDs with a wavelength of 300 nm up to 380 nm and a group of short-wave UV LEDs with a wavelength from 240 nm to 300 nm and a control unit for switching LEDs and adjusting their brightness, to ensure the accuracy of identifying gemstones of different nature and origin based on an analysis of the photoluminescence pattern under UV excitation ...

It is desirable that the UV LEDs are arranged symmetrically and alternately on a common holder around the camera and lens. This ensures uniform illumination of a large area of precious stones and / or jewelry of a large size.

It is preferable that LEDs for illumination of white (visible) light are additionally located in the body of the device.

Alternatively, the device additionally includes a retractable platform with a pallet for placing objects under study on it.

It is desirable that the surface of the camera and the pallet be covered with a dark, non-luminescent material.

As an option, UV LEDs are equipped with UV optical filters.

The brightness of the LEDs is controlled by changing the constant current or by pulse-width modulation of the current passing through them.

A schematic representation of the structure of one of the variants of the device is shown in Fig. 1 for the following device positions

1 - Retractable platform with pallet.

2 - LEDs for illumination.

3 - UVA LEDs with a set of optical filters.

4 - UVB LEDs with a set of optical filters.

5 - Transmitting video camera with a lens and a set of optical filters.

6 - The body of the device.

7 - Control unit for switching and dimming LEDs.

8 - Power supply unit.

9 - Receiving device (PC, tablet, mobile phone, etc.).

Observation of photoluminescence of diamonds is carried out in a closed, darkened housing 6, which houses a pull-out platform with a tray 1 with analyzed diamonds or jewelry containing diamonds or other precious stones. The surface of the pallet 1 and the inner walls of the housing 6 are covered with a dark, non-luminescent material. In the upper part of the body 6 there is a sensitive, color, digital video camera 5 with a lens aimed at the analyzed diamonds and a set of optical filters in the visible range. This video camera 5 records the image of luminescent diamonds in the visible range. The lens focuses on the analyzed crystals. Two groups of UV LEDs 3 and 4 are used as sources of photoluminescence excitation. In the described embodiment of the device, UV LEDs 3 and 4 are located symmetrically in the upper part of the camera on a common holder around the video camera 5 with a lens. Their radiation is directed to the tray 1 with the analyzed diamonds (or any other minerals). This ensures uniform illumination of the pallet 1 with diamonds. One group of LEDs 3 emits light in the long-wavelength range (300-380 nm), the other group of LEDs 4 emits light in the short-wavelength range (240-300 nm). Light from LEDs 3 and 4 can pass through optical filters of the UV range (not shown in the drawing). They do not transmit visible electromagnetic radiation, which could interfere with the observation of diamond luminescence, which improves identification accuracy. A digital video camera 5 transmits an image of luminescent diamonds via a communication channel (wired or wireless) to a computer (tablet, smartphone, etc.). Its screen displays the appearance and color of glowing diamonds. In the described embodiment, the device additionally contains a backlight LED 2 (or several LEDs) of white (visible) light. This illumination is used to produce visible light images of crystals on a pallet. Adjustment of the brightness of LEDs 3 and 4 is carried out by changing the control unit 7 direct current or by pulse-width modulation of the current passing through LEDs 3 and 4.

Due to the use of two groups of LEDs 3 and 4 with different radiation ranges and control of the switching unit 7 and LED brightness adjustment, various possible modes of checking gemstones are provided, which provides an analysis of a wide range of photoluminescence levels of gemstones, and therefore their accurate identification by composition, nature and origin with the possibility of simultaneous analysis of a large number of products.

The use of the described device makes it possible to quickly and accurately identify and distinguish between genuine natural diamonds, synthetic diamonds and refined diamonds, as well as other precious stones. Analysis methods include the study of fluorescence and phosphorescence of diamonds under the influence of UV radiation. As sources of excitation of photoluminescence of crystals, two groups of semiconductor LEDs are used - sources of long-wave UV (300-380 nm) and short-wave UV (240-300 nm) radiation. It is possible to adjust the excitation intensity by changing the LED current. The photoluminescence picture of the crystals is recorded by means of a digital video camera equipped with a lens. The luminescence pattern is displayed on a computer screen or other video surveillance device. The light detector is configured to reproduce the spectral sensitivity of human vision. The determination of the origin of the diamond is carried out by the operator of the device based on the analysis of the photoluminescence color.

The UV LEDs are located symmetrically at the top of the camera on a common holder around the camera and lens. The appearance and color of luminescent diamonds are displayed on the computer screen (tablet, smartphone). The digital camera control is configured to accurately reproduce the crystal luminescence color. LEDs of two UV ranges (long-wave UV (300-380 nm) and short-wave UV (240-300 nm)), which is used to compare luminescence patterns. By using several LEDs in each group, a uniform UV illumination of the tray with crystals is achieved. The number of LEDs can vary, depending on many factors, such as case size, LED power, camera capabilities, etc. By controlling the LED power supply current, UV excitation intensity is controlled to provide analysis of a wide range of photoluminescence levels of diamonds and other stones, for getting an accurate result. The need for such a control is caused by the fact that, other things being equal, the photoluminescence intensity of different diamond crystals can differ by several orders of magnitude. This is mainly determined by the large difference in the lifetime of nonequilibrium charge carriers due to the influence of various channels of nonradiative recombination, as well as by the difference in the concentrations of luminescent optical centers. The luminescence of strongly luminescent diamonds is more accurately observed at a low excitation level, and the luminescence of weakly luminescent diamonds - at a high excitation level.

It is desirable to observe visually the luminescence of diamond in conditions of strong shading and long-term adaptation of the user's vision. In addition, the dimensions of most jewelry crystals are several millimeters - it is difficult to see the details of the luminescent picture of the crystal with the naked eye. Therefore, implemented in the described device, the correct solution for observing photoluminescence is to use a highly sensitive, color, digital video camera equipped with a lens.

The image from the video camera is transmitted to a computer (tablet, smartphone ...) via a communication channel (wired or wireless in different versions of the device). The computer screen can additionally display an image of a tray with crystals in the visible range (when illuminated by a white light LED) for comparison with the luminescence pattern. Also on the screen as a help, you can display reference materials on the luminescence of crystals.

However, using a camcorder poses two problems. First, the camcorder must transmit the color of the luminescence to the computer screen without distortion - as they are perceived by the eye. This can be achieved in a variety of ways. The simplest is the software correction of the color sensitivity of the camera. The second problem is more complicated - the dynamic range of the camera's sensitivity (from noise level to saturation level) is much narrower than that of the human eye. It is limited by the capacity of its analog-to-digital converter and usually does not exceed two or three orders of magnitude. At the same time, the difference in the luminescence intensity of different crystals can be much larger. At a low excitation level, it can happen that the luminescence of a strongly luminous crystal fits into the dynamic range of the camera's sensitivity, but the luminescence of a weakly luminous crystal is not visible. And at a high level of excitation, the luminescence of a weakly luminous crystal will fit into the dynamic range of the camera's sensitivity, while the image of a strongly luminous crystal will be overexposed. With overexposure, the signal is saturated in all three multi-colored pixels of the triad, which appears in the image as white. That is, when overexposure, a distortion of the luminescence color occurs. This disadvantage is observed in most devices for detecting the photoluminescence pattern of crystals, including diamonds. In the case of analysis of a single crystal, this problem can be solved by choosing the exposure time. When analyzing a group of crystals that differ greatly in luminescence intensity, this approach is no longer suitable. In the proposed device, this problem is solved by adjusting the level of UV excitation. It is carried out by changing the current through the LEDs, since the glow intensity of UV LEDs is almost linearly dependent on the current through it. The user manually selects it so as to comfortably visualize the color picture of luminescence, but not bring it to overexposure. In different versions of the device design, either direct current regulation or its pulse-width modulation is performed. The LED current control knob is located on the device body. Also on the body of the device there is a power switch and a switch that allows supplying a supply current to: a) a white light LED, b) a group of long-wave UV (300-380 nm) LEDs, c) a group of short-wave UV (240-300 nm) LEDs.

The experience of observing the photoluminescence of a large number of diamonds under UV excitation has shown that practically all natural diamonds luminesce with violet, blue and blue light (short-wavelength photoluminescence - CFL), synthetic (HPHT, PFCO) diamonds either do not glow at all, or luminesce in green, yellow, orange or red light (long-wavelength photoluminescence - DPL). Refined natural and synthetic diamonds glow brightly with green, yellow, orange or red light (DPL). In addition, it was found that short-wave UV (240-300 nm) excitation usually causes effective photoluminescence of synthetic crystals, long-wave UV (300-380 nm) excitation usually causes effective photoluminescence of natural crystals. These features are determined by the difference in the impurity-defect structure of natural, synthetic and refined diamonds and the ability of UV radiation of different wavelengths to excite different impurity-defect optical centers.

Thus, the presence of diamond luminescence, its color and comparative intensity upon excitation in the long-wavelength UV (300-380 nm) and short-wavelength UV (240-300 nm) ranges allows, in accordance with the algorithm presented in Table. 1, to separate natural diamonds from synthetic (HPVT, PFKHO) and refined diamonds. Table 1 shows all possible combinations of the results of a luminescence study upon excitation of diamonds in the long-wavelength UV (300-380 nm) and short-wavelength UV (240-300 nm) ranges. Theoretically, combinations of results are possible when, upon excitation in these two ranges, luminescence of two different colors is observed: CPL (short-wavelength luminescence) and DPL (long-wavelength luminescence). In this case, such diamonds should be subjected to additional research using other methods of gemological research.

Table 1

Luminescence at long wavelength UV (300-380 nm) excitation Luminescence at short-wave UV (240-300 nm) excitation Diamond identification result CFL CFL Natural CFL Not Natural CFL DFL More research needed Not CFL Natural Not Not Synthetic Not DFL Synthetic or refined DFL CFL More research needed DFL Not Synthetic or refined DFL DFL Synthetic or refined

An additional identifying feature is the presence of phosphorescence (prolonged afterglow) of the diamond after turning off UV excitation. Phosphorescence is characteristic of synthetic diamonds.

In one embodiment, a diamond identification device operates as follows. Place diamonds or diamond jewelry on the pallet. The pallet is pushed into the darkened chamber of the device. Using a switch, a current is applied to the white light LED and a picture of the arrangement of the crystals on the tray is photographed. Then the switch is switched to the position of power supply of LEDs of the long-wave UV (300-380 nm) range. With the help of the current regulator, the LED power supply increases the excitation intensity. A picture of the photoluminescence of crystals located on the tray is observed on the screen of a computer (tablet, smartphone) connected to the device. When one of the crystals begins to luminesce, correlate it with the crystal in the image of the visible range, note the color of its luminescence, and determine which range it belongs to - CFL or DPL? This is done with all crystals located on the pan as the level of excitation increases. At the maximum excitation level, all non-luminescent crystals are noted. At the next stage, the switch is switched to the position of supplying the LEDs of the short-wave UV (240-300 nm) range. Repeat the above procedure, fixing the presence and color of luminescence or absence of luminescence. According to the algorithm described in table. 1 determine the origin of the diamonds. Thus, a large number of products are checked simultaneously and a high accuracy of identification of gemstones of different nature and origin is obtained on the basis of the photoluminescence pattern under UV excitation.

Claims (9)

1. Device for identifying precious stones, characterized by the fact that it includes devices located in the body: a power supply, a transmitting video camera with a lens for transmitting an image to a visual display device, a source of exciting radiation in the form of a group of long-wave UV LEDs with a wavelength of 300 nm up to 380 nm and a group of short-wave UV LEDs with a wavelength from 240 nm to 300 nm, as well as a control unit for switching LEDs and adjusting their brightness to ensure accurate identification of gems of different nature and origin based on analysis of the photoluminescence pattern under UV excitation ... 2. Device for identifying precious stones according to claim 1, characterized in that the UV LEDs are arranged symmetrically and in alternating order on a common holder around the video camera with the lens. 3. Device for identifying precious stones according to claim 1, characterized in that white light LEDs are additionally installed in the body of the device. 4. The device for identifying precious stones according to claim 1, characterized in that the device additionally includes a pull-out platform with a pallet for placing the objects under investigation thereon. 5. Device for identifying precious stones according to claims 1, 4, characterized in that the surface of the pallet and the inner walls of the housing are coated with a dark non-luminescent material. 6. The gemstone identification device according to claim 1, characterized in that the UV LEDs are equipped with optical filters in the UV range. 7. The device for identifying gemstones according to claim 1, characterized in that the brightness of the UV LEDs is controlled by varying a constant current. 8. Device for identifying gemstones according to claim 1, characterized in that the brightness of the UV LEDs is controlled by pulse-width modulation of the current passed through them. 9. Device for identifying precious stones according to claim 1, characterized in that after switching off the excitation source, phosphorescence is detected if the decay time of the radiation is on the order of seconds or longer.

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