OPTICAL-PROPERTIES OF UNDOPED AND CO-DOPED V(A)-VI(1-X)A-VI(X)A-VII(A) SINGLE-CRYSTALS

Undoped and Co-doped V(A)-VI1-X(A)-VI(X)A-VII(A) single crystals were grown by the vertical Bridgman technique using ingots synthesized from mixtures with 8.6 mol % of excess iodine. The single crystals have or thorhombic crystal structure and the indirect energy band structure. T he composition dependence of the energy band gap was well described by the equation, E(g)(X) = E(g)(0) - AX + BX2. The impurity optical abso rption peaks from the doped cobalt in the single crystals were assigne d to electron transitions between the energy levels of Co2+ ions and C o3+ ions sited at the T(d) symmetry point in the host lattice.