Feature of the structure of the crystal lattice of potassium sulfate crystals is presence of two nonequivalent cation knots [1]. They differ with coordination number on oxygen: 9 and 10, accordingly. It is known that bivalent ions of the transitive metals having not-filled valency d-cover, for example copper and manganese, selectively replace potassium ions in knots with a big coordination number [2,3]. Ionic radiuses of rare-earth elements are smaller than ionic radius of potassium [4], therefore they can replace them in the crystal lattice. In works [5,6] it is shown that samarium ions form in matrix of potassium sulfate two types of impurity in luminescence centers. There are two alternative explanations to it: samarium ions replace cations in various knots, or indemnification of a superfluous charge at one of heterovalency impurity of an ion is carried out by molecules of structural water.
The purpose of the given work is studying of the role and influence of trivalent ions of samarium and gadolinium, and as prehistories of samples on radiating – stimulating processes.
Monocrystals of potassium sulfate, activated by ions of trivalent samarium and gadolinium have been grown from the sated water solutions. The activator was added in an initial solution in the form of soluble salt in water SmCl3 or GdCl3. The similar choice of activating salts is caused by that sulphatic salts of rare-earth elements are almost insoluble in water and have a return temperature course of solubility. The attempts to grow monocrystals of potassium sulfate by adding in a solution of sulphatic salts of rare-earth metals haven't led to success. Ions of rare-earth elements were not built in the crystal lattice of potassium sulfate. It is known that chlorine ions enter the crystal lattice K2SO4. It is established by electrophysical methods of measurement of ionic conductivity and methods of analytic chemistry [7,8]. In work [9] it is shown that presence of chlorine ions in the lattice of potassium sulfate crystals doesn't lead to occurrence of strips of optical absorption in the field of its transparency. It is known [10, 11] that ions of halogens lead to some increase in a relative quantum exit of X-ray-luminescence of the potassium sulfate and to redistribution of the saved up light – sum in peaks TSL. Ions of halogens don't lead to occurrence of new peaks on the recombinational luminescenceson curve TSL. Their influence speaks of occurrence of additional cation vacancies [11,12].
In Figure 1 the spectrum of absorption of monocrystal K2SO4 of the three-valency ion of the samarium activated by ions (0,1 moth of %) is resulted. From figure it is visible that in the field of matrix transparency in the activated crystal there are three strips of absorption. At room temperature their maxima are at 4,30 eV, 4,48 eV and 5,49eV. It is known [5,6] that at excitation of potassium sulfate crystal activated by ions of samarium in these strips of absorption there occurs photoluminescence. At excitation in a long-wave strip of absorption the luminescence maximum at temperature 80К is in area 3,12 eV. Photoluminescence is raised in two other strips of absorption with maximum 3,54 eV. Thus, spectra of absorption, excitation and photoluminescence radiation testify that samarium ions form two types of centers of luminescence. In potassium sulfate crystals, activated by ions of gadolinium the spectrum of optical absorption is qualitatively similar to one presented in Figure 1. At room temperature there are observed three strips of absorption with maxima at 4,32 eV, 4.48 eV and 5,49 eV.
Figure 1. Spectrum of absorption of crystal K2SO4-Sm3+
at
room temperature
In Figure 2 the typical curve of thermostimulated luminescences K
2SO
4-Sm is resulted. For this monocrystal it is difficult enough to figure recombinating processes. Curve TSL has the expressed maxima recombinating luminescences at temperatures 145К, 190К, 220К and 280-300К. On its low-temperature wing there is an excess, testifying about presence of one more peak of luminescence in area 100К. Peaks TSL with maxima at 190К and 280-300К are characteristic for pure crystals K
2SO
4 (see, for example, [13]). In pure crystals dominating peak of luminescence is radiation with maximum at 300К.
Thus, in the activated monocrystal there were new peaks of recombinating luminescences at 100К, 145К and 220К. In the crystals activated by ions of gadolinium, at the dose of irradiation 10 kGr on curve TSL one strongly pronounced maximum recombinated luminescences is observed at rate-rature 155К. On its low-temperature wing there is a «shoulder». Its occurrence is connected with presence of peak TSL with maximum in area 100К. In comparison with monocrystal of potassium sulfate activated by samarium, the kind of curve TSL for monocrystal K2SO4-Gd looks essentially easier. However, the dominating peak on curve TSL of potassium sulfate activated by ions of gadolinium, is abnormal the big width on temperature that assumes it nonsimplicity. As it was mentioned above, pure potassium sulfate crystals have maxima on curve TSL at 190К and 280-300К. At the sample activated by ions of gadolinium, the peak recombinating luminescences with maximum at 190К aren’t allocated, in area 280-300К recombinated the luminescence has small lightsum.
Figure 2. Curve TSL of crystal K2SO4-Sm3+ after
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