Optical properties of undoped and Co2+-doped Cd2GeSe4 single crystals

Cd2GeSe4 and Cd2GeSe4:Co2+ (Co: 0.2, 0.3, 0.4, and 0.5 mol %) single crysta ls with a rhombohedral (hexagonal) structure were grown by the vertical Bri dgman method. The structural and optical properties of Cd2GeSe4:Co2+ (Co: 0 .2, 0.3, 0.4, and 0.5 mol %) were characterized by x-ray diffraction and op tical absorption measurements at room temperature (298 K). The lattice cons tants, a(0) and c(0), increased when increasing Co2+ in the Cd2GeSe4:Co2+ c rystal to 0.3 mol %. They increased sharply when increasing Co2+ to 0.4 and 0.5 mol %. The optical energy band gap of the Cd2GeSe4:Co2+ crystal decrea sed when increasing Co2+ in the Cd2GeSe4:Co2+ crystal to 0.3 mol % and it a lso decreased sharply when increasing the amount of Co2+ to 0.4 and 0.5 mol %. Two impurity optical absorption bands were observed at wavelength range s of 1300-1900 nm and 700-900 nm. These bands originated from the Co2+ ions located at the C-3v symmetry point in the Cd2GeSe4:Co2+ crystal. (C) 2001 American Institute of Physics.