Koketai T.A., Tussupbekova A.K., Baltabekov A.S., Imangaliyeva N.N.

Karaganda State University named after academician Ye.A.Buketov

STUDY OF RECOMBINATION PROCESSES IN METAPHOSPHATE OF POTASSIUM CRYSTALS

In crystalline and vitreous metaphosphate of potassium, recombination processes are associated with the decay of the same radiation defects. A change in the type of structure leads to a change in the sign of the recombination process: in the crystalline process, the hole process; in the glassy sample – electronic [1]. The influence of impurity ions usually leads to the appearance of new peaks of thermally stimulated luminescence (TSL) and a change in the accumulation of light densities in peaks of recombination luminescence of the matrix.

The most important result of the study of recombination luminescence in crystalline and vitreous Currol salts is the establishment of a change in the mechanism of recombination from hole to electron, respectively. Impurity ions of transition metals are traps for electrons.

A study of the role and effect of other ions of transition metals (Co²⁺ and Ni²⁺) on recombination processes in potassium metaphosphate was carried out on crystalline samples.

Figure 1a shows the X-ray luminescence spectrum for a crystalline Currol salt, activated with nickel sulfate. It can be seen from the figure that there is a pronounced maximum at 3.54 eV. The radiation characteristic of a matrix with a maximum at 3.1 eV manifests itself as a "shoulder" on the longwave wing of the main emission band. In addition, a weak luminescence is observed in the region of 2.6 eV, which we associate with the presence of impurity sulfate anions in samples. The spectral composition of the TSL peak, measured in the temperature range 100-110 K, consists of the same three emission bands 2.6 eV, 3.1 eV, and 3.54 eV. The last emission band is obviously due to the presence of nickel impurity ions in the crystals. The influence of nickel ions on recombination processes in the crystalline salt of Currol is similar to that observed in samples activated by manganese ions. This allows us to conclude that impurity Ni²⁺ in potassium metaphosphate are also traps for electrons. This is associated with an increase in the rate of accumulation of the light sum in the peaks of TSL. The appearance of a luminescence with a maximum at 3.54 eV indicates a hole character of the recombination processes in this temperature range. The ions of manganese and nickel, captured by irradiation of samples with X-ray quanta, are the centers of recombination. Therefore, in the Currol salt, depending on the nature of the activator, emission bands of 3.46 eV and 3.54 eV appear, which disappear in the spectral composition of the TSL peaks in glassy samples.

Fig. 1 - X-ray luminescence spectra for crystalline KPO₃-NiSO₄ (a) and KPO₃-CoSO₄ (b) salts measured at 80 K

The spectral composition of X-ray luminescence for a KPO₃-CoSO₄ crystal is shown in Fig. 1b. The dominant emission band in this sample is the band with a maximum at 3.61 eV. In general, the spectral composition of X-ray luminescence and TLC peaks in all crystalline samples activated by ions of transition metals is similar. An exception is the change in the position of the radiation band, which we associate with the recombination of holes at the Me ⁺ centers. In samples activated by manganese ions, it is at 3.46 eV, nickel ions - 3.54 eV and cobalt ions - 3.61 eV.

An analysis of these results allows us to state that transition metal ions in Currol salts are traps for electrons. Depending on the type of structure, the role of radiation-induced impurity centers of recombination processes changes. In the crystalline salt of Currol, the defects of Me⁺ are the centers of recombination, which lead to the appearance in the spectral composition of the peaks of TSL, a new band of radiation whose positions depend on the nature of the impurities.

In a glass-like sample, the centers of Me⁺ become electron donors. In this case, in the spectral composition of the TSL peaks, the emission band associated with the recombination of holes on radiation-induced in impurity centers disappears. In addition, a new peak of TSL appears, the temperature maximum of which depends on the nature of impurity ions of transition metals.

References

1. Baltabekov A.S., Koketaitegi T.A., Kim L.M. The influnce of impurity ions of transition metals on radiation induced prosseces // Eurasian technical journal. - 2010. - Vol.7, №2(13). – P.12-18.