Кoketai T.A., Тussupbekova A.K., Ismailov Zh. T., Nukygazy S.A., Mussina G.I.

Karaganda State University named after academician Y.А.Buketov,

Republic of Kazakhstan, Karaganda

The absorption spectra of the luminescence excitation and emission of the KDP crystals

Potassium dihydrogen phosphate (KH₂PO₄ or KDP) crystals are considered as one of the most important construction materials in modern technology. The following problems which appear after this require a behavior forecast of construction materials in extreme conditions and modification of physical properties or creation of new materials with specific features. Research objects are single crystals of potassium dihydrogen phosphate and transition metal’s ions activated KDP crystals. КDР crystals maintains nonlinear optical properties. Some modern devices have found the usage to various single crystals from KDP [1]. The simplest method to change optical, mechanical or electrical properties of crystals is introduction of various substitution impurities or ionizing radiation exposure.

The growth of KH₂PO₄ single crystals was produced of saturated aqueous solutions using isothermal evaporation of the solvent at 40⁰C. Given temperature conditions of growth were taken from research work [2]. After 10-12 days this process there were 5 mm to 40 mm sized crystals.

Our work in particular included measurements of the absorption spectra of the luminescence excitation and emission at different temperatures which were used from the optical research methods. Absorption spectra of crystals and induced absorption spectra in the area of 200 – 800 nm were measured using photoelectron method on spectrophotometer SPh-16 by standard methods [3]. Additional absorption spectra were measured towards non radiated crystals. The last one took place to learn the influence of ionizing radiation on impurity absorption. Measurement of the absorption spectra was done at 80 – 320 K temperature range.

Fig. 1 shows traditional TSL curves for KDP crystals, activated by Me²⁺ ions. Comparison of experimental results shown on Fig. 1 alongside with the TSL curve for a pure KDP [4] shows that recombination processes in activated crystals are doing some noticeably rapid changes. There are some new TSL peaks in crystals with bivalent manganese impurity ions in areas of 140 K, 210 K and 230 K (Fig. 1, curve 1). In pure KDP crystals the lightsum of recombined glow at this temperature range is not severely noticeable. The activated KDP-Mn²⁺ crystal obtains the lightsum of the low temperature peak which is noticeably more towards the matrix peak at 180 K. In crystals with bivalent cobalt impurity ions (Fig. 1, curve 2) there is a new peak in the TSL at 140 K which is clearly defined. TSL peaks which are considered normal for the matrix with maxima at 180 K and 290 K are slightly suppressed. The low-temperature peak of the recombined luminescence has a maximum at 110 K.

Fig. 1. TSL curves of activated KDP crystals. Radiated dose – 150 kGy.

In crystals with bivalent nickel (Fig. 1, curve 3), a new peak in the TSL appears as a “shoulder” in the high-wing emission peak with a maximum at 110 K. Thermal annealing carried out at 100 – 110 K for pre-irradiated X-rays of the sample allows selecting a new peak emission. It is a maximum of 140 K. TSL peak, which is normal for the matrix with maxima at 290 K, is depressed. Recombined luminescence peak with maximum at 190 K is dominant at accumulated lightsum.

KDP pure crystals get colored under the ionizing radiation. Three observed absorption bands have the maximum points at 2.26 eV, 3.17 eV and 5.75 eV. The received results are as expected in the papers [4], according to which DKDP crystals have been detected to obtain radiation navigated absorption bands at 230 nm, 390 nm and 550 nm (5.39 eV, 3.18 eV and 2.25 eV). In [5] research work it is shown that radiation navigated absorption bands are conditioned with absorption in B-radicals at 2.26 eV, 3.17 eV and with interstitial hydrogen atoms at 5.75 eV.

The temperature dependence of the absorption band for the activated crystal is different from that in a pure sample. The given outcome is considered as a direct proof to the fact that Co²⁺ ions increase the thermal stability of B-radicals in KDP crystals. Analogous outcome was received for KDP-MnSO₄ crystals. From all the facts mentioned above, there is only one recombined luminescence appearance peak at 140 K which is related to the influence of transition metal ions. Its observing does not depend on the nature of transition metal impurity ions.

References

1. Singh, P., Hasmuddin, M., Vijayan, N., Abdullah, M.M., Shakir, M. and M.A. Wahab, 2013. Investigation on growth features and crystal structures of pure and metal ion (Mn²⁺) doped KDP single crystals. Optik, 124. P. 1609-1613.

2. Rez, I.S. and V.I. Pachomov, 1967. The growth of single crystals of KDP with different modifiers. Bulletin of Acad. Of Science USSR, 31(Physics). P. 68-72.

3. Zaidel, A.N., G.V. Ostrovsky and Yu.I. Ostrovsky, 1972. Technique and practice of spectroscopy. Moscow: Nauka. P. 376.

4. Chirila, M.M., Garces, N.Y., Halliburton, L.E., Demos, S.G., Land, T.A. and H.B. Radousky, 2003. Production and thermal decay of radiation-induced point defects in KD₂PO₄ crystals. J. Appl. Phys., 94(10). P. 6456-6462.

5. Kim, L.M. and B.S. Tagayeva, 2008. Radiation-induced absorption bands in KDP crystals. Bulletin of University of Karaganda, 4 (Physics). P. 21-26.