irradiation X-rays dose 50 кGг
In Figure 3 spectra of absorption for monocrystal K2SO4-Sm are resulted at temperature of liquid nitrogen before and after irradiation in X-ray quanta. At temperature 80К impurity absorption does not make qualitative changes. In spectrum the same three strips of absorption are observed, only at temperature fall there was a displacement of their maxima aside shorter lengths of waves. At temperature of liquid nitrogen maxima of these strips of optical absorption are at 4,35 eV, 4,54 eV and 5,32 eV.
Figure 3. Spectrum of absorption of crystal K2SO4-Sm3+ at temperature 80К before irradiation (1) and after irradiation in X-ray quanta with dose 100 kGг (2) and 150 кGг (3)
As a result of absorption irradiation in X-ray quanta of new strips it is not revealed. At ionizing radiation influence reduction of optical density in strips impurity absorption is observed. Apparently from Figure 3, changes in absorption spectrum increase with growth of the dose of the irradiation. The similar behavior of optical absorption speaks reduction of concentration trivalent impurity ions, i.e. as a result of the irradiation their recharge occur ionizing radiation.
It has appeared that recombinational processes in crystals K2SO4-Sm depend on a prehistory of samples. In Figure 4 typical curve TSL for the powdery sample of the potassium sulfate activated by ions of samarium is resulted. Before measurement the sample has been subjected to thermal processing. Initial monocrystals have been ground in powder which within 1-1,5 hours was maintained at temperature 600 °С. As a result of such thermal processing curve TSL has undergone qualitative changes. Apparently from Figure 4, peaks TSL with maxima at 100К, 145К and 220К have disappeared.
Peak recombinating luminescences were shown at 135К and in area 170К. It is known that after heating of potassium sulfate to temperature of polymorphic phase transition from α – structures of the crystal lattice in β, at photoexcitation there is the luminescence in green area of spectrum which authors of work [14] connect with occurrence of the molecular centers of luminescence S2. It is supposed that at high-temperature thermal processing of potassium sulfate there occur thermochemical processes.
As we didn't heat up samples to the temperature of structural phase transition, hence, changes on curve TSL can't be connected with the centers of type S2. After heating samples were slowly cooled, i.e. their training wasn't made.
Therefore it is impossible to connect changes in recombinating processes after thermal processing with the advent of additional vacancies in knots of the crystal lattice. Qualitative changes of curve TSL (see figure 2 and 4) are connected with removal from crystal of structural water. Ions of the trivalent samarium replace in lattice of potassium sulfate ions K+. Local indemnification of charge can be made cations vacancies. As crystals were grown up from water solutions in these vacancies water molecules can be grasped.
Figure 4. Curve TSL of crystal K2SO4-Sm3+ after
preliminary thermal processing at 600˚С.
Irradiation dose – 50 kGr
In Figure 5 the spectrum of absorption of crystal K2SO4-Sm is presented at room temperature after thermal processing at temperature 200 °С within days. Heating of the monocrystal activated by ions of the samarium, to more high temperature leads them to cleaving. It is interesting to notice that the same doesn't occur for not activated crystals. Comparison of spectra of absorption before thermal processing shows that there was a redistribution of optical density in strips impurity absorption.
Theoptical density in a long-wave strip of absorption has decreased, and in two short-waves – has increased. The assumption that the given strips of absorption are connected with absorption impurity of samarium ions, occupying nonequivalent knots doesn't allow explaining for some reasons observable redistributions of optical density. Firstly, the total area under curves of the optical absorption presented in Figure 5, before and after thermal processing remains invariable. Secondly, if impurity ions are distributed on cation knots casually the transfer from one type cation knot to another can't have a certain orientation.
Reduction of concentration of the samarium in potassium sulfate doesn't lead to qualitative changes in spectrum of absorption which would testify that they occupy primary cation knots of one of two possible types. Thirdly, electronic transitions in ions of rare-earth elements are caused by transitions with blank f – covers which is shielded valency electrons
Figure 5. Spectrum of absorption of crystal K2SO4-Sm3+ at room temperature to (1) and after thermal processing (2)
Therefore, for essential change of power level there is not enough change of coordination number on a unit. Fourthly, essential changes of kind of curve TSL before thermal processing can be explained change of element structure of studied substance. Similar effects of preliminary heat treatment are observed in the crystals activated by ions of gadolinium. Thus, it is established that at activation of the potassium sulfate crystals by trivalent ions of samarium and gadolinium, in the crystal lattice there is structural water. Water molecules, settling down near impurity ions, not only compensate the superfluous charge, but also form one of the centers of luminescence. It is shown that under the influence of ionizing radiation samarium ions in matrix of potassium sulfate are recharged. Impurity of the radiating – induced centers form the peak recombinated luminescences on curve TSL.
Work is executed under the grant of fund of basic researches of the RK Ministry of Education and Science.
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