Optical absorption spectra of Cr³⁺ ions in LiNaSO₄ and LiKSO₄ crystals

Abstract

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.