NVS-CRF38 br Introduction In the work presented crystals

Introduction In the work presented, crystals of the silico-sillenite Bi12SiO20 (BSO) doped with Fe3+ ions have been studied. The sillenites are non-centrally symmetrical oxides Bi12MO20±δ (M=Si, Ge, Ti) with the lattice symmetry corresponding to the spatial group I23 [1,2]. In the entirely stoichiometric sillenite crystals, the M ions are tetravalent (x=1, δ=0). At this the bismuth NVS-CRF38 having the end electronic configuration 6s2(1)6p3(3)6d0(5) (numbers in brackets stand for the amount of hybrid orbitals, the superscripts denote the number of electrons in the orbitals) is transformed into the Bi3+ ion in the sillenite lattice. This allows it to donate three electrons from three 6p orbitals for the formation of chemical bonds with surrounding ligands (oxygen ions) [3]. The Bi3+ ion coordination number is 7 (Fig. 1) [2]. The coordination and charge state of bismuth described above mean that three of seven chemical bonds of bismuth are to be sigma-bonds with oxygen ions. Other four bonds are donor-acceptor (coordination) bonds. So, the hybridization of the Bi3+ ion is 6p3(3)6d0(4) in the sillenite lattice. In this case, the hybridization state of the O2– ions bonded to Bi3+ is forcedly 2s2(1)2p4(3), which gives a chance of electron pair transfer from the hybrid orbital to the bismuth unoccupied orbital to form the coordination bond (Fig. 2). The M ion forms four sigma-bonds with the oxygen ions (Fig. 1), in particular, Si4+ ion being in the 3s2(1)3p2(3) state forms these bonds. The detailed consideration of the Bi12SiO20 crystalline lattice shows that the silicon ion is surrounded only with 4-coordinated oxygen ions, while 7-coordinated bismuth ion is surrounded with both 4- and 3-coordinated oxygen ions. But despite this fact, all the oxygen ions are in the 2s2(1)2p4(3) hybridization state, each having two hybrid orbitals with electron pairs. Both electron pairs form coordination bonds in the case of 4-coordinated oxygen ions, while in the case of 3-coordinated oxygen ions one electron pair remains lone (Fig. 1). The research into the sillenite crystals doped with iron ions is of particular interest as the iron is a conventional background impurity in these compounds [4,5]. Besides, the doping with iron changes optical, electrical and magnetic properties of the sillenites causing the substantial diversification of their applications [6]. But, currently, there is no established view in the literature if the Fe3+ ion in the sillenites is a donor with the Fe4+ ion as a final state or if it is an acceptor with Fe2+ ion as a final state [7]. The paper presented is concerned with the study of the magneto-optical properties of the Bi12SiO20 silico-sillenite crystals and the consideration of the iron ion state in their crystalline structure. The magnetic properties of the iron ions have been studied in details for many compounds, particularly in the hemoglobin. In this context some information on the hemoglobin magnetic properties is relevant. The iron ions play an important role in these properties formation, not only determining the red color of the blood but also being responsible for the oxygen transportation by the blood cells. The spin states for the different charge states of the iron ions in the hemoglobin molecule [8] are presented in Table 1. The iron ion is located in the center of the octahedron structure in the hemoglobin molecule and is able to change the charge state [8]. The total spin of Fe3+ in heme is equal to 5/2 as, according to Hund\'s rule, all 5 electrons of Fe3+ ion occupy different d-orbitals. It is to be noticed that the d-orbitals do not participate in the hybridization, although one of the d-electrons is involved into the formation of a sigma-bond with carbon monoxide. As a consequence, the iron oxidation state changes from 2+ in the octahedron surrounding to 3+ after the CO addition (Table 1). The d-orbitals do not participate in the hybridization (although one of the d-electrons is involved into the bond formation) due to the fact that the atoms of transition metals possess incomplete 3d-electron shells. In particular, the iron atom has six 3d-electrons instead of ten. This is because of the fact that the 3d-state energy is higher than that of 4s-states, so the filling of 4s-orbitals with electrons starts before the filling of 3d-shells is finished. This electron configuration gives 3d-electrons a possibility to donate their electrons into the chemical bond formation without participating in the hybridization. Particularly, in the iron ion the hybrid orbitals of the heme octahedron are formed from the 4s2(1)- and 4p0(3)-orbitals.