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LiuLabs MDIS-f8 Multifunction Dual Integrating Sphere Spectrometer

LiuLabs MDIS-f8 multifunction dual integrating sphere spectrometer (US Patents 7,652,755, 7,388,656)

The LiuLabs MDIS-f8 multifunction dual integrating sphere (MDIS) spectrometer is the most advanced gemological instrument controlled by the artificial intelligence software with 8 functions of spectral measurement, color measurement, UV fluorescence measurement, photoluminescence (PL) measurement, color grading of gemstones, color grading of colored diamonds, color grading of jadeite, and alexandrite effect grading. The patented dual integrating sphere optical arrangement (Fig. 1) provides the best possible illuminating and viewing geometry under a controlled measurement environment for measuring the spectrum and color of faceted colored diamonds and gemstones.  The LiuLabs spectrometer is an essential instrument for gemological laboratories to do spectroscopy, UV fluorescence, photoluminescence, and colorimetry researches, and to grade color and identify gemstones, diamonds, and jadeite, as well as to grade alexandrite effect.

Figure 1. The dual integrating sphere optical arrangement.

The color grading software can simulate the human visual color grading method to grade the color by “considering” the parameters of faceted gemstones, such as shape, size, refractive index etc, through a neural network. The spectrometer is calibrated by a patented novel three-step method. The Gem spectrometer can accurately and precisely measure the spectral reflectance, calculate the CIELAB data, determine the average color grade, and then provide the true color grade by the fuzzy logical method. The average color represents the color of the gem material, and the true color represents the face-up color, i.e. the “Key color” for faceted colored gemstones, and the “Characteristic color” for colored diamonds.

The LiuLabs spectrometer is also designed to measure the color of any rough gemstones, minerals and crystals. In addition, the measured spectral reflectance can be used for spectroscopic research and gem identification.

The Liulabs spectrometer is a high precision instrument developed for laboratory applications, but designed in a compact size for portable applications. The compact design and universal power input make the spectrometer very versatile for being used by gemological researchers, gemologists, mineralogists, diamond and gemstone buyers in diamond and gemstone mines, jewelry markets, gemstone factories, trade shows, jewelry stores, and any place as long as where there is a power outlet. The spectrometer can be carried in a suitcase with all necessary accessories.

Figure 2 shows the measurement window of the Liulabs spectrometer. The measured spectrum of a faceted synthetic ruby has two bands centered at about 480 nm and 730 nm, and an absorption maximum at about 560 nm. The long wavelength band with the spectral peak at 693 nm is a fluorescence band caused by visible light. The calculate hue angle, saturation and lightness in the CIELAB color space are 355.870, 28.07 and 16.84.  The average color of the measured synthetic ruby is Fancy Purplish Brown, and the true color grade is Intense Purplish Pinkish Red.

Figure 2. The measurement window of the spectrometer; 1. Spectrum; 2. Shape, size, and RI; 3. Colorimetric data;  4. Color Monitor button; 5. Color Measurement button ; 6. Average Color Grade; 7. True Color Grade; 8. Fluorescence or photoluminescence base line adjustment.

A colored diamond color grading plug-in software is provided for the LiuLabs Spectrometer. The software can automatically calculate the “Characteristic color” for colored diamonds, and determines the “Fancy Color Grade” using the fuzzy logic algorithm and a look-up-table. The color grading accuracy and precision of colored diamonds by the spectrometer is much better than that by human color graders. Figure 3 shows a typical measurement window for color measurement and color grading of colored diamonds. 

The measured spectral reflectance is very useful for colored diamond identification. Depending on the color and the absorption peaks of the colored centers in the visible region, such as the N3, H3, H4, 550 nm, NV, SV, and GR1 centers, most colored diamonds can be identified as natural, synthetic, treated or other mixed types by this spectrometer.

 

Figure 3. The color measurement and color grading screen for colored diamonds. The average color of the diamond is Fancy Intense Greenish Blue, and the color grade is Fancy Vivid Greenish Blue.

 

UV Fluorescence and Photoluminescence Measurements

The Liulabs spectrometer can measure VU fluorescence and photoluminescence (see Figure 4). The radiation sources are light emitting diodes (LED) at 255 nm, 290 (310) nm and 365 nm for UV fluorescence measurement, and at 400 nm, 465 nm, 525nm and 585 nm for photoluminescence measurement. A 405 nm laser diode is also used for photoluminescence measurement. The plug-in software of the UV fluorescence and PL measurements provides high magnitudes of UV fluorescence or photoluminescence measurement at X1, X10, X100 and X1000  to enhance the measured UV fluorescence spectrum or PL spectrum. The UV fluorescence spectrum or PL spectrum of diamonds and gemstone is often enhanced, because UV fluorescence and PL of gemstones are usually very weak. Enhanced UV fluorescence or PL spectra of diamonds is particularly useful for identifying CVD and synthetic diamonds.

Figure 4 shows the UV fluorescence of a pink synthetic diamond under the 290 nm LED with the magnitude X100. The fluorescence band in the long wavelength range is caused by the N-V center, and the 575 nm peak is the zero phonon line of the N-V center. Except a very few natural type IIa pink diamonds with very low saturation have the N-V center, all natural pink diamonds do not have the N-V center, thus, the pink diamond can be identified as treated synthetic diamond. 

Figure 4. UV fluorescence measurement of a pink synthetic diamond under a 290 nm LED at the magnitude X100.

 

Identification and Color Grading of Jadeite

The LiuLabs spectrometer can be used to grade the color of jadeites, and to identify dyed only jadeites (C type) as well as impregnated and dyed jadeites (B+C type) (see Figure 5). Since FTIR cannot identify dyed jadeites, the LiuLabs spectrometer is more useful than a FTIR spectrophotometer, besides the LiuLabs spectrometer can grade the color of jadeite.

 

Figure 5. Spectra of dyed and natural green jadeites measured by the LiuLab Spectrometer.

Figure 6 shows the window of jadeite color grading  by both the Universal Color  System and the China Standard GB T23885-2009. The window of jadeite color grading allows an operator to adjust color area percentage and curve shape for accurate color grading in the color area. The surface of most jadeite jewels and carvings are curved, which shall be adjusted for accurate color measurement and grading. The window provides a scroll bar for adjusting the curve degree of a jadeite to input its curve shape for obtaining accurate color grade.

Figure 6. Color grading of jadeite.

 

Alexandrite Effect Grading


The Liulabs spectrometer has a function of grading the alexandrite effect among the CIE standard illuminants A, D65, F7 and F11 (see Figure 7). There are 6 alexandrite effects between different CIE standard illuminants, and 5 grades based on the hue angle differences in the CIELAB color space. The 5 grades of the alexandrite effect are None, Weak, Intense, Strong, and Vivid. The hue angle change ranges of the 5 alexandrite effect grades are:

Grade

Hue Angle Difference

None

< 20

Weak

>= 20 and < 40

Intense

>= 40 and < 60

Strong

>= 60 and < 80

Vivid

>= 80

 

Figure 7. Alexandrite effect grading by the Liulabs spectrometer.

 

The MDIS - f8 spectrometer is the most valuable multifunctional instrument for all gemological and mineralogical laboratories, gemologists, and mineralogists due to its multifunction of spectral measurement, UV fluorescence measurement, PL measurement, color measurement, color grading, and alexandrite effect grading of all colored diamonds and gemstones. The measured reflectance, UV fluorescence, and PL spectra are the key for gem identification and gemological research. It is the only spectrometer that can enhance UV fluorescence and PL spectra, and can grade the color of colored diamonds and gemstones, as well as jadeite. A gemological laboratory can do most, if not all, spectral measurement, UV fluorescence measurement, PL measurement, colorimetric measurement, color grading of colored diamonds, color grading of gemstones, alexandrite effect grading tasks by the MDIS - f8 spectrometer for gemological research, colored diamond and gemstone identification, color grading purposes without any other instruments, such as Roman spectrometer, FTIR spectrometer, XRF spectrometer, fluorescence spectrometer, colorimeter, and other more expensive instruments.

 

Specifications:

Wavelength Range:                  380-760 nm

Extend Wavelength Range:        230 -800 nm

Color Space:                            CIELAB

Spectral Calibration:                 Three-step method

Color Grading Terminology:        Universal Color Grading System

Input Parameters:                    Shape, size, and  RI

Spectrometer:                          CCD detector

Thermal Stabilizer:                   45 oC

Computer:                               Windows PC

Software:                                LiuLabs Spectrometer Version 1.6.8

Plug-in Software:                     Colored diamond color grading software 

                                             UV fluorescence and photoluminescence measurement software

                                             Jadeite color grading software

                                             Alexandrite effect grading software

UV Radiation Sources:              255, 290(310), and 365 nm LED with integrating hemisphere

PL Radiation Sources:               400, 465, 525, and 585 nm LED with integrating hemisphere

Size:                                      Potable 260 x 250 x 90 mm (9.85" x 10.24" x 3.55")

                                             Laboratory 470 x 300 x 90 mm (18.52" x 11.82 x 3.55")

Weight:                                  Portable 3 Kg (6 lb)

                                             Laboratory 4 Kg (8lb)

Power Requirements:                100-240 V, 50-60 Hz, 50 VA

                                             100-240 V, 50-60 Hz, 100 VA (with the thermal stabilizer)

 

 

References

1.      Y. Liu, Apparatus and method for color measurement and color grading of diamonds, gemstones and the like, US Patent No. 7,652,755, 2010.

2.      Y. Liu, Apparatus and method for color measurement and color grading of diamonds, gemstones and the like, US Patent Publication No. 2008/0204705.

3.      Y. Liu, Method and system for color grading of gemstones, US Patent No. 7,388,656, 2008.

4.      Y. Liu, Optical filter for CIE daylight simulator, US Patent No. 7,378,784, 2008.

5.      Y. Liu and K. Hurwit, The TrueGemColor system: A new computer color imaging system based on a uniform CIELAB color space for color grading of gemstone, Z. Dt. Gemmol. Ges. Vol. 57, No. 3-4, pp. 133-142, 2008.

6.      Y. Liu et al., Identification of dyed jadeite using visible reflection spectra, J. Gemmology, Vol. 31, No. 5-8, pp. 181-184, 2009.

7. Y. Liu et al., Color measurement of a ruby, Color Research and Application, http://onlinelibrary.wiley.com/doi/10.1002/col.21743/full.

 

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Last modified: 01/07/13.