RU2110059C1 - Luminescent method determining concentration of glow centers in oxygen-carrying materials - Google Patents

Abstract

FIELD: spectral analysis. SUBSTANCE: proposed method includes excitation of luminescent impurities and inherent defects by electron beam which duration amounts to 0.1 radiation time of life of most short-lived glow center, registration of luminescence, exposure of characteristic bands in spectrum of luminescence, identification of glow centers, measurement of intensities of standard and of characteristic bands, determination of concentration with usage of data on calibration samples. Fundamental wide-band glow of tested material which duration is less than radiation time of glow centers is chosen as internal standard of sensitivity. EFFECT: improved authenticity of method. 7 dwg , 1 tbl

Description

 The invention relates to methods for determining the concentration of impurity and intrinsic defects in oxygen-containing materials, in particular to a luminescent method for determining the concentration of glow centers, and can be used for technological control of substances and in ecology to control ice and water.

 A known luminescent method for determining the concentration of glow centers [1], in which one of the operations of the method is the standardization of measurements (ie, bringing the fluorimeter to the same sensitivity). To standardize the spectrofluorimeter, standards are produced, which are blocks of plastic matrices with the introduction of molecular organic substances in them.

 The disadvantage of this method is that an external standard is used in the standardization operation, i.e. it is necessary to change the standard and install the test sample in the measuring cell of the spectrometer. This reduces the accuracy of the measurements, and there are additional costs of working time and materials in the preparation of standards.

A known method of measuring the concentration of an impurity [2], in which the radiation of a sample excited by a light source, is fed to two photodetectors, the output signals of which are measured. The concentration of the object is determined by the calibration graph based on the measured signal ratio of both photodetectors. To eliminate the error due to changes in sensitivity, the ratio of the signals of the photodetectors is normalized to the ratio of the signals of the same photodetectors. Concentration is measured by the formula
C _x = C _e [U $\genfrac{}{}{0ex}{}{\text{uh}}{\text{2}}$ U $\genfrac{}{}{0ex}{}{\text{uh}}{}$$\genfrac{}{}{0ex}{}{}{\text{01}}$ / U $\genfrac{}{}{0ex}{}{\text{uh}}{\text{1}}$ U $\genfrac{}{}{0ex}{}{\text{uh}}{\text{02}}$ ] / [U ₁ U ₀₁ / U ₂ U ₀₂ ],
where u $\genfrac{}{}{0ex}{}{\text{uh}}{}$$\genfrac{}{}{0ex}{}{}{\text{01}}$ and U $\genfrac{}{}{0ex}{}{\text{uh}}{\text{1}}$ - signals of the main detector when measuring the standard; U $\genfrac{}{}{0ex}{}{\text{uh}}{\text{02}}$ and U $\genfrac{}{}{0ex}{}{\text{uh}}{\text{1}}$ - signals of the additional detector when measuring the standard; U ₀₁ , U ₁ and U ₀₂ , U ₂ - similar values for measurement with a sample.

The disadvantage of this method is the low sensitivity (10 ^-5 - 10 ^-7 %), as well as the complexity of the optical registration scheme.

The closest analogue is the luminescent method for determining the concentration of luminescence centers in oxygen- and fluorine-containing crystals [3]. The method includes sampling, excitation of luminescent impurities by an electron beam, the duration of which is 0.1 radiative lifetime (τ) of the shortest-lived luminescence center, registration of luminescence, identification of luminescence centers by the magnitude of the radiative time within the characteristic band, measurement of the standard intensity and characteristic bands and determination of concentration using data from calibration samples. A power density of at least 6 • 10 ³ W and a pulse duration of 0.1 radiative time provide a transition of the quantum system of impurity centers to a completely excited state, which makes it possible to increase the sensitivity of the analytical method for determining the concentration of impurity emission centers and extend the range of measured concentrations 10 ^-2 - 10 ^-11 %.

 One of the operations of the method consists in measuring a standard (sample with a predefined composition of defects) and in preparing a sample of the test substance for analysis. To do this, a crystal is cut out in the form of a plate with a cross-sectional area equal to the cross-sectional area of the standard. Due to the error in installing the crystal in the measuring cell and from pulse to pulse of the instability of the electron beam, approximately (5%) the measurement accuracy of the luminescent spectral-kinetic analyzer decreases to ± 10%. In addition, the disadvantage of this method is the cost of working time and materials for preparing the sample for analysis.

 The aim of the invention is to increase the accuracy of measurements while reducing measurement time and cost of sample preparation.

 This goal is achieved by the fact that in the known method, including the excitation of luminescent impurities by an electron beam, the duration of which is 0.1τ, registration of luminescence, identification of characteristic bands in the luminescence spectrum, identification of luminescence centers, measurement of reference intensities and characteristic bands, determination of concentration using data according to calibration samples, the internal standard of sensitivity choose their own fundamental broadband glow of the investigated material, the duration of which is less than the radiative time of the glow center.

 Due to the fact that the test sample and the standard are combined in one sample, that is, the intrinsic sensitivity standard is the intrinsic fundamental broadband luminescence of the studied material, the duration of which is less than the radiative time of the glow centers, the measurement accuracy is increased and the time spent on working and materials for sample preparation is reduced (use new, previously unknown standard in the operation of the method).

 It was previously known [4] to use the intrinsic fundamental glow of oxide materials to obtain a continuous emission spectrum in solid-state electron-optical emitters. No technical solutions were found in which the indicated new feature was used for this purpose, which indicates the significance of the differences.

As established by direct research, the effect is achieved due to the unique properties of the fundamental glow
1. It is excited by the action of electron beams of nano- or picosecond durations in almost all materials containing oxygen ions O (namely: in crystals of Al ₂ O ₃ , YAlO ₃ , CaO, Y ₃ Al ₅ O ₁₂ , BeAl ₂ O ₄ , Mg ₂ SiO ₄ , Gd ₂ Sc ₂ Al ₃ O ₁₂ and others; in minerals, glasses and quartz: in ceramics YBa ₂ Cu ₃ O _7-b ; in H ₂ O (ice, water).

2. A structureless broadband luminescence is observed from 190 to 1200 nm with a constant quantum yield (0.6 • 10 ^-3 ) with the same amplitude over the entire spectral range and radiative time <10 ps. It should be noted that when excited by electron beams, the duration of the fundamental emission corresponds to the duration of the exciting pulse.

 3. It does not depend on temperature in the range from the temperature of liquid nitrogen to the melting temperature of the material.

In FIG. 1 shows oscillograms of an Al ₂ O ₃ (Ti) crystal; in FIG. 2 - calibration graphs for determining the content of impurities Ti, V, Cr in leucosapphire; in FIG. 3 - waveform of a crystal of Al ₂ O ₃ (F ⁺ ); in FIG. 4 - Al ₂ O ₃ (F); in FIG. 5 - Y ₃ Al ₅ O ₁₂ (Pr); in FIG. 6 - calibration graphs for determining the content of Ce, Pr impurities in garnet; in FIG. 7 is an oscillogram of a solution of water with fluorescein.

 The method is as follows.

A sample sample based on a crystal of any kind, shape, and size is installed in the measuring cell of a spectral setup with nanosecond resolution and the cathodoluminescence (CR) spectrum is recorded, and the kinetic characteristics of the glow centers are measured. To excite luminescent centers, an electron accelerator with beam parameters is used: current density 0.01–2 kA / cm ² , electron energy 60–300 keV, with a specific pulse duration equal to 0.1 of the lifetime of the shortest-lived luminescence center. The lower limit of electron energy is due to the properties of fundamental broadband radiation (at 60 keV, a narrowing of the continuous spectrum begins to appear); the upper one is the stability and invariability of the structure of the substances under study (when the electron energy in the beam exceeds 300 keV, new radiation defects will be created in the material under study). The lower limit of the current density of the electron beam is determined by the minimum value of the current at which the necessary radiation intensity is still achieved for the registration system, the upper limit is determined by saturation of the intensity of the emitting centers. Then, the characteristic bands in the CR spectrum and their radiative times (kinetics) are revealed. Using the table, which provides information on the spectral and kinetic characteristics of impurity centers and intrinsic defects, the bands are identified with one form or another of an impurity or defect. The intensity of the standard and the characteristic band according to the waveform are measured in one pulse of irradiation. With this method of measurement, the error is determined only by the accuracy of the oscillography. A high-speed (resolution applied 1 ns) digital oscilloscope is used, which includes a twelve-digit analog-to-digital converter and an IBM-PC personal computer (AT-286). The quantitative content of the impurity is determined by the calibration curve and the ratio of the measured intensities.

Example 1. A sample of a sample based on an Al ₂ O ₃ crystal is installed in a measuring cell of a spectral setup. The pulse duration in the excitation mode is 2 ns. The electron energy is 300 keV, the current density is 2.0 kA / cm ² . Using the table, which contains information on the spectral characteristics of impurity centers in leucosapphire, bands with one or another type of impurity are identified.

Thus, an impurity of titanium with a characteristic band λ = 315 nm and τ = 195 ± 55 ns is recorded in the test sample. The intensity of the standard (I _o ) is measured - the fundamental radiation with τ = 2 ns and the characteristic band (I) with λ = 315 nm and τ = 195 ± 55 ns according to the oscillogram from a computer monitor, for one radiation pulse.

In FIG. Figure 1 shows an oscillogram of an Al ₂ O ₃ (Ti) crystal. The quantitative content of titanium impurities is determined by the calibration curve, by the ratio of the measured intensities (I _o / I) shown in FIG. 2. The measurement error on a digital oscilloscope (analog-to-digital converter with a personal computer IBM-PC (AT-286) was ± 0.1%.

Example 2. In the proposed variant of the method, the execution conditions are similar to example 1. But in the excitation mode, a pulse is formed with a duration of 0.8 ns. The electron energy is 250 keV, the current density is 1 kA / cm ² . In the Al ₂ O ₃ sample under study, the intrinsic defect of the F ⁺ lattice is detected — a center with a characteristic band of λ = 330 nm and τ = 9 ns. In FIG. Figure 3 shows the oscillogram of an Al ₂ O ₃ (F ⁺ ) crystal. The quantitative content of F ⁺ centers is determined by the calibration graph, according to the ratio of intensities I _o / I. The measurement error did not exceed ± 0.1%.

Example 3. In the proposed variant of the method, the execution conditions are similar to example 1. But in the excitation mode, a pulse with a duration of 100 ns is generated. The electron energy is 200 keV, the current density is 0.5 kA / cm ² . In the Al ₂ O ₃ sample under study, an intrinsic lattice defect is detected in the F ⁺ center with a characteristic band of λ = 420 nm and τ = 36 ms. In FIG. Figure 4 shows an oscillogram of an Al ₂ O ₃ (F) crystal. The quantitative content of F ⁺ centers is determined by the calibration curve, by the ratio of the measured intensities (I _o / I). The measurement error did not exceed ± 0.1%.

Example 4. The range of analytes can be expanded, as well as the range of defined elements. In the proposed variant of the method, the execution conditions are similar to Example 1. But in the excitation mode, a pulse with a duration of 2 ns is formed, the electron energy is 150 keV, the current density is 0.05 kA / cm ² , and a sample sample based on a Y ₃ Al ₅ crystal is installed in the measuring cell O ₁₂ (Pr). The intensity of the standard (I _o ) is measured - the fundamental glow with τ = 2 ns and the characteristic band with λ = 360 nm and τ = 28 ns (I), according to the oscillogram of FIG. 5. The quantitative content of impurities in the garnet crystal is determined by the calibration curve (Fig. 6). The measurement error was ± 0.1%.

Example 5. In the proposed variant of the method, the execution conditions are similar to Example 1. But in the excitation mode, a pulse of 0.4 ns in duration, an electron energy of 60 keV, a current density of 0.01 kA / cm ^{2 is formed} , and a solution of water with fluorescein is installed in the measuring cell. In the next step of the method, the intensities of the standard (I _o ) are measured - a fundamental glow with a duration of 0.4 ns and a characteristic band with λ = 527 nm and τ = 4 ns (I), according to the oscillogram (Fig. 7). The measurement error was ± 0.1%.

 Thus, the proposed method allows to increase the accuracy of measurements, reduce energy consumption, quickly analyze the substance.

 In addition, the proposed method is simple and does not require special sample preparation and a large amount of the analyte.

 Sources of information.

 1. Levshin L.V., Saletsky A.M. Luminescence and its application: Molecular luminescence. - M.: From Moscow State University, 1989, p. 227.

 2. SU, copyright certificate N 1341556, cl. G 01 N 21/62, 1985.

 3. RU, patent N 1795738, cl. B 01 N 21/62, 1990.

 4. Baryshnikov V.I., Schepina L.I., Kolesnikova T.A., Martynovich E.F. FTT. - 1990. - T. 32. - N 6. - S. 1888-1890.

Claims (1)

 Luminescent method for determining the concentration of luminescence centers in oxygen-containing materials, including the excitation of luminescent impurities and intrinsic defects by an electron beam, the duration of which is 0.1 of the radiative lifetime of the shortest-lived luminescence center, registration of luminescence, identification of characteristic bands in the luminescence spectrum, identification of luminescence centers, measurement of intensities standard and characteristic bands, determination of concentration using data by degrees different samples, characterized in that the internal standard of sensitivity select their own fundamental broadband glow of the material under study, the duration of which is less than the radiative time of the glow centers.

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