The thermoluminescence (TL) of pure and doped NaF crystals has been intensively investigated for the last years, however, in many works the spectral distribution of the emission was not studied and the interpretation of the glow peaks is often contradictory /l/.This note gives some new results concerning the influence of oxygen ions o n the T L process. N a F single crystals were grown both in vacuum and air atmosphere from the reactive of high purity. All the samples were X-irradiated up t o l x l 0 R. The absorption spectra were measured on a Unicam SP8-100 spectrophotometer. Cooled photomultipliers sensitive in the range of 180 t o 800 nm were used while studying the TL; the constant heating rate was 1 0 K/min. The spectral composition of the emission was analysed using a MDR-2 monochromator. (Fig. 1); these bands are ascribed to O--V: complexes. At LNT there is also an absorption band a t 196 nm, conditioned by 0--ions. N a F ( 0 2 ) samples (NaF(vacuum), subjected to a prolonged thermal treatment in the air) show new absorption bands at 255 and 3#55 nm (curves 3 and 4 in Fig.
EPR-spectra of X-irradiated potassium dichromate crystals are studied a t various temperatures froin RT to LNT. The most intensive lines are interpreted as due to radicals Cr0:-(A-lines) and CrO; (C-lines), resulting from Cr,O, owing to X-irradiation. Hyperfine structure of C-line, due to interaction of unpaired electron with Cr53 nucleus, occurs at low temperatures, and new unobserved earlier Q-lines appear near-by C-line. The spectrum
Earlier (ALYBAKOV et al.; ALYBAKOV, SHARSHEEV) we have studied the EPR spectra of irradiated undoped LiNaSO., and LiKSO, single crystals. This paper presents the results concerning the optical absorption spectra of C?+ ions doped in these crystals.LiKSO, and LiNaSO, single crystals were grown from saturated aqueous solutions doped with Cr,(SO,), . 6 H,O in amounts of 1.5 g/1 and 0.2 g/l, respectively. Both crystals had green colour. Absorption spectra were measured on Unicam SP8-100 spectrophotometer using a nitrogen cryostat. Figure 1 shows absorption spectra of doped crystals. In both cases spectra are qualitatively similar and consist of four absorption bands. These bands positions are given in Table 1.In principle, impurity C?' ion in LiKSO, and LiNaSO, crystals can substitute either Li', or K + (Na+)ion. It is known (KLIMOVA et al.) that in LiKSO, crystals potassium ions occupy octahedral cavities and lithium ions occupy tetrahedra of SO,'-anions. Absence of some splitting in optical absorption spectra at the liquid nitrogen temperature and observation of EPR spectra of doped crystals at the room temperature are indicative of octahedral co-ordination of C$+ ions. Two strong and wide absorption bands in the visible region, characteristic of C?' in octahedral co-ordination, were observed also in other ionic crystals (SVIRIDOV et ah). Hence, we can conclude that Cr3+ ions enter the mixed lithium-potassium and lithium-sodium sulphates substituting K + and Na' ions, respectively.
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