Circular Dichroism in Magnesium Sulfite Hexahydrate, Doped with Cobalt

摘要

The new nonlinear crystal of magnesium sulfite hexahydrate (MgSO_3.6H_2O) belongs to the rare crystallographic class C_3 (without a symmetry centre), the other known only representative being sodium periodate (NaIO_4). There are some scarce data in the scientific papers about magnesium sulfite hexahydrate's physical properties. Single crystals of significant sizes (up to 40 - 50 mm) of MgSO_3.6H_2O as well as such, doped with Ni, Co, and Zn, for the time being are grown only by our own method developed in the Laboratory for Crystal growth at the Faculty of Physics of Sofia University. Recently we have observed the supposed presence of optical activity. Circular dichroism is not observed in pure MgSO_3.6H_2O. The results of the first ever investigations are presented, which demonstrate the presence of circular dichroism in MgSO_3.6H_2O doped with Co. The circular dichroism appears in the spectral range from 420 nm to 580 nm. The spectrum of circular dichroism demonstrates a well expressed structure - an isolated maximum at 470 nm and a combination of two overlapped maxima at ~ 495 nm and 520 nm respectively. The spectrum of the circular dichroism is compared with the absorption spectrum of MgSO_3.6H_2O:Co, along the direction (0001) and with the linear dichroism spectrum measured in direction(1210). It is shown in this way that the circular dichroism appears only in thernspectral range of the optical absorption structure due to Co dopant. In the same spectral range can be observed also the linear dichroism determined by Co presence in MgSO_3.6H_2O.