Luminescence excitation spectra and characteristics of luminescence centers with overlapping absorption bands

Abstract

535.37+548.4For an ensemble of different types of luminescence centers with overlapping absorption bands, with no restrictions on the optical densities, we have obtained relations describing the luminescence excitation spectra for each type of center. We consider transformations of the relations in some limiting cases. We suggest a procedure for using the equations obtained to determine the characteristics of the luminescence centers. Some of these procedures have been experimentally implemented in study of intrinsic radiation color centers in lithium fluoride crystals. We have determined the ratios of the luminescence quantum yields for F 2 and F 3 + color centers, and we have observed that a major role is played by nonradiative transitions in deactivation of the first excited singlet state of F 3 + centers.Key words: luminescence excitation spectrum, equation for the excitation spectrum, luminescence centers with overlapping absorption bands, methods for determining characteristics of luminescence centers.Introduction. Methods based on absorption and emission of electromagnetic radiation are widely used in scientific practice, for example, for investigation of the structure of matter, intramolecular and intermolecular interactions, impurity and intrinsic structural defects in solids. Such methods are the basis for sensitive methods for determining the constituent composition of different materials. Many monographs present reviews of the basic characteristic features of luminescence and the possibilities for using them to solve scientific and practical problems (see, for example, [1,2]).Measurements of the photoluminescence (PL) or photoluminescence excitation spectra and practical use of such measurements tend to be done for samples with optical density less than unity. When this condition is not met, the excitation spectrum does not correspond to the absorption spectrum; there is no proportionality between the photoluminescence intensity and the absorption coefficient, i.e., the concentration of the component. The situation is even more complicated if the absorption spectra of several luminescence centers overlap in this case.Overlap of the absorption spectra for several centers is encountered rather frequently in the studied samples. It does not always seem possible to decrease the overall optical density of the sample down to a value much less than unity. For example, when impurity and/or intrinsic defects (arising as a result of technological operations or other external factors) are studied in a solid, samples must be studied containing all existing luminescence centers, each characterized by their own spectra, including overlapping spectra, and their own absorption values. Technological operations in the sample can be carried out at small depths (on the order of a few micrometers), and in this case several types of luminescence centers are created with overlapping absorption spectra and an overall optical density on the order of a few units (see, for example, [3]). In such cases, we need to know the conne...

Quantitative luminescent analysis methods

“…In the first case, equations are used that determine the changes in the photoluminescence intensities as a result of re-absorption of photoluminescence in the analyte medium [5]. In the second case, the methods are based on the dependence of the photoluminescence intensity on the absorption coefficients of a multicomponent medium, [6,7]. From the relations obtained in [5][6][7], equations are derived that make it possible to find the absorption coefficients of a medium from the measured intensity.…”

“…In the second case, the methods are based on the dependence of the photoluminescence intensity on the absorption coefficients of a multicomponent medium, [6,7]. From the relations obtained in [5][6][7], equations are derived that make it possible to find the absorption coefficients of a medium from the measured intensity.The problem of finding the absorption coefficients according to the procedure outlined above is an inverse problem. In order to properly solve inverse problems with original data obtained experimentally with random errors,…”

“…In those equations and in the next two equations in this section, the ratio of the frequencies ν i and ν m should appear, as follows from Eq. (8) derived in [6]. However, if the measurements of the photoluminescence intensities are made in units of the number of photons, then the ratio of the frequencies in Eqs.…”

“…Let us consider the problem of determining the absorption coefficients from measurement data for the photoluminescence excitation spectra. The relation describing the connection between the photoluminescence intensity at the frequency ν det , for a substance found in a multicomponent absorbing medium, and the absorption of this medium is given in [6,7]. Let us rewrite it in the following form for a medium containing two components, one of which can be a luminescent probe:…”

“…First we should mention the analytical relations obtained in [5][6][7], connecting the photoluminescence intensities and the absorption coefficients of the analyte medium. Without these relations, it would have been impossible to develop the proposed methods.…”