Method for registration of absorption spectra of small luminescent specimens

FIELD: registration of absorption spectra of small luminescent specimens.

SUBSTANCE: the absorption spectrum of small luminescent specimens is determined according to relation of intensities of light fluxes that have passed and not passed through the specimen, the luminescence of the standard specimen is used as the specimen through which the radiation flux has not passed, and the luminescence of the examined is used as the specimen through which the radiation flux has passed, and the absorption spectrum of the examined specimen is calculated according to the respective mathematical formula.

EFFECT: expanded functional potentialities due to the increase of the range of specimens suitable for measurements without special preparation of them.

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The invention relates to the field of physico-chemical methods of analysis of small and hard-to-luminescent objects by the spectra of their optical absorption. The method can be used for analysis of liquid, amorphous and crystalline substances, such as diamonds small size, complex shape, or partially contained in the pot or rock that is necessary for their quality assessment, classification and sorting.

There is a method of determining the concentration of N3-defects in diamonds, which as the probing radiation is used rentgenolyuminestsentnye studied diamond, and the determination of the absorption coefficient is from the baseline, restored for a-band rentgenolyuminestsentnye on the wings of the analyzed lines (Vphotos, Uphow, Mfrow, X-ray method of determining the concentration of nitrogen defects in diamond; RF Patent №2215285, G 01 N 23/00, Application No. 200210652 from 13.03.2002,, publ. 27.10.2003). The method allows to avoid losses and errors in the scattering and reflection at the input radiation in the crystal, therefore, allows to determine the concentration of nitrogen defects in diamond arbitrary shape and small size.

The disadvantage of this method is the inability to obtain in this way the absorption spectrum. Determination of the absorption coefficient in this way is only on DL is not wave bisphenol line N3 centers (415.3 nm). In addition, the measurement accuracy of this method is low because the measurement error of up to 200%. In the description of the invention the authors rightly point out that the method is suitable only an approximate estimate of the concentration of N3 defects.

The closest in technical essence and the achieved result is a well-known method for recording absorption spectra passing through the investigated sample radiation from an external source. (See for example, ASI. Applied physical optics. M: Fizmatgiz, 1961, str-417, or Levshin L.V., A. M. Saletsky Luminescence and its measurement. - M.: Publishing house of Moscow state University, 1989, str-218). This method is implemented by sequential or simultaneous recording is not passed through the sample flow of radiation transmitted through the sample flow radiation and calculation of the absorption spectrum of the sample from the Bouguer law:

where- absorption spectrum (cm-1);

Io(λ) - the intensity of the failed sample radiation at a wavelength of λ ($);

I(λ) is the intensity transmitted through the sample radiation at a wavelength of λ ($);

d is the thickness of the sample is determined by the dimension (cm).

This method allows you to obtain the absorption spectra in a wide range, has high accuracy and is widely used.

Not the balance of the known method are restrictions on the size and the need for special preparation of samples for measurement. For measurements, the sample must be flat polished parallel surfaces, which is necessary to accurately determine the thickness of the sample and to reduce the effect of scattering and reflection on the accuracy of the measurements. In addition, the sample must be, first, the relatively large size (a few millimeters) for measurements, secondly, a sufficiently small size to place it in the spectrometer (a few centimeters). Many natural samples, such as diamonds, as a rule, are crystals of small size, flat faces are not always (figa), in crystals often cracks and inclusions, so measurements of the spectra of optical absorption is possible only in a limited number of large enough samples of the required forms. On the other hand, there is a need to investigate the absorption of the samples, which are partially enclosed in any larger object, extract from which is not feasible: for example, a diamond to be concluded in cutting tools, diamond enclosed in a piece of jewelry (figb), the diamond can be enclosed in the piece of rock (pigv). For such situations, the method is not applicable.

An object of the invention is to enhance the functionality of the method by increasing the range suitable for measurement of samples without aspecially training.

This objective is achieved in that in the method of determining the absorption spectra of small luminescent samples based on optical absorption relative intensities of failed and passed through the sample flows radiation, as not passed through the sample radiation flux is used, the luminescence of the reference sample, as transmitted through the sample radiation flux is used, the luminescence of the sample, and the absorption spectrum is calculated by the formula:

where:- absorption spectrum of the sample (cm-1);

d - the size of the sample (cm);

I(λ) - flow of rentgenolyuminestsentnye the sample at a wavelength of λ ($);

Io(λ) - flow of rentgenolyuminestsentnye reference sample at the wavelength (λ) (at. e);

k is a normalizing factor such that k=I(λ)/Io(λ) when

The invention is illustrated by the following considerations.

The intensity of the luminescence transparent (not absorbing) of the object is increased linearly with the increase of its thickness (figa, dependence b=0). If the crystal has an absorption, the dependence of the intensity of its luminescence from the size and rate of pogles the Deposit becomes non-linear (figa, according to b=1, b=2, b=5), and nonlinearity will be the greater, the larger the crystal size and the rate of its absorption. For large values of the absorption intensity of luminescence of the absorbing material generally ceases to depend on the sample thickness, as in this case is logged only the illumination of the surface layers (figa, dependence b=5). However, if the sample is small and has a relatively small indicators absorption, at a distance r1from him it can be considered isotropic point source, therefore, we can replace luminescense sample such point source with intensity of luminescence Io, placed in the centre of the sample. The emission of this source in the x direction will be attenuated according to the law of Bouguer absorbing layer is equal to half the thickness of the sample (figb).

Substituting in the law of Bouguer Io(λ) - measured intensity of the luminescence of the reference sample at a wavelength of λ, I(λ) - measured intensity of the luminescence of the sample at the same wavelength and half the thickness of the crystal (d/2), normalizing selection coefficient k obtained spectra so that the ranges without absorptionfind the absorption spectrum of the investigated crystal:

Thus, knowing the luminescence spectrum of the sample without being absorbed (standard) and the luminescence spectrum of the sample with absorption (sample), is calculated absorption spectrum of the sample from the Bouguer law, taking d half its thickness.

The source of excitation of luminescence choose depending on the analyte. Such a source may be, for example, laser, x-rays, electron beam, etc. the requirement of the source, is its ability to excite the luminescence of the reference sample.

The method is illustrated in figure 1, 2, 3, 4, 5.

Figure 1. (a) the Form of natural rough diamonds size 1-0 .5 mm. b) Diamond with a diameter of about 0.8 mm at the rim. in) Diamond size is about 1 mm in a piece of kimberlite.

Figure 2. a) the intensity of the luminescence of the absorbing sample, depending on its thickness and absorption coefficient. b) calculating the propagation of waves in an absorbing medium.

Figure 3. Installation scheme for the registration of the absorption spectra.

Figure 4. (a) Spectra of rentgenolyuminestsentnye studied diamonds, b) normalized spectrum of rentgenolyuminestsentnye one of the studied diamonds with absorption in comparison with the spectrum of the crystal reference.

Figure 5. Absorption spectra of diamonds obtained according to this method: (a) with N3 defects; b) H3 defects and pogashenie orange region of the spectrum.

Technical implementation of the method is demonstrated on the example of the study of small (1-0 .5 mm) diamond (figa), including the jewel in the frame (figb) and crystal diamond, partially enclosed in kimberlite (pigv). Luminescence was excited by x-ray radiation. Spectra were recorded with a fluorescent spectrometer, the scheme of which is shown in figure 3. The sample 1 was placed directly on the beryllium window of the source of excitation of luminescence 2 (portable x-ray equipment REIS). The condenser 3 radiation was collected on the entrance slit of the monochromator 4, then entered the photomultiplier tube 5 and through the interface block 6 were entered into the computer 7. Registration spectra rentgenolyuminestsentnye sample and crystal pattern made by standard methods of registration of luminescence spectra. The size of the investigated crystals (size (d) was measured by an optical micrometer. As the reference spectrum used range of diamond that does not have absorption in the investigated range, and with intensive rentgenolyuminestsentnye. This spectrum was recorded in the computer memory as a reference file.

Then recorded the luminescence spectra of the samples (figa). After registration these spectra selection factor k normalized so that they coincided with what pectrum rentgenolyuminestsentnye reference crystal on the spectrum, where absorption is negligible. An example of normalization (upper curve on figa) shown in figb. Normalization factor determined from the condition

k=I(λ)/Io(λ) when

Becausethen taking for Io(λ) the luminescence spectrum of the reference crystal, and I(λ) spectrum of the sample, by calculating the above formula for each wavelength, found a range of absorption coefficientsdefects.

On figa shows the absorption spectra obtained in the final result. As follows from figa, the spectra are dominated by absorption N3 defects (of 415.3 nm), observed characteristic features of N2 (345 nm) and N4 (474 nm) centers. The spectra correspond to the literature data about the absorption of diamonds.

On figb is obtained similarly absorption spectra of diamonds dominated by absorption H3 defects (maximum at 480 nm) and absorption in the orange region (550-650 nm).

A feature of this method is that its accuracy increases with decreasing sample size and decreasing the absorption coefficients. With increasing sample size and absorption coefficient in it the accuracy of the method decreases, but when the crystal size up to 5 mm and the absorption coefficient up to 5 cm-1the relative error of measurements is n the more ± 5%.

Method for recording absorption spectra of small luminescent samples relative intensities are not past and past through the sample flows radiation, characterized in that the quality is not passed through the sample radiation flux is used, the luminescence of the reference sample, as seen through the thread object radiation is used, the luminescence of the sample, and the absorption spectrum of the sample is calculated according to the formula ′α(λ)=(2/d)·Ln{k·lo(λ)/l(λ)},

where ′α(λ) - absorption spectrum of the investigated sample (cm-1);

d - the size of the investigated sample (sm);

I(λ) - the intensity of the luminous flux of rentgenolyuminestsentnye the sample at a wavelength of λ ($);

Io(λ) - the intensity of the luminous flux of rentgenolyuminestsentnye reference sample at the wavelength (λ) ($);

k is a normalizing factor such that k=I(λ)/Io(λ) when ′α(λ)=0.



 

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