OPTICAL-PROPERTIES OF AGGASE2 AND AGGASE2-CO2+ SINGLE-CRYSTALS

The temperature dependence of the optical energy gaps in AgGaSe2 and AgGaSe2:Co2+ single crystals has been investigated. The impurity optical absorption of AgGaSe2:Co2+ has also been studied. In the temperature dependence of the energy gaps, the temperature coefficients (dE(g)/dT) are measured to be 1.8 X 10(-4) eV/K (10-60 K) and -3.2 X 10(-4) eV/K (95-300 K) for the AgGaSe2, and 8.9 X 10(-5) eV/K (10-60 K) and -1.0 X 10(-4) eV/K (80-300 K) for the AgGaSe2:Co2+, respectively. In the optical-absorption spectrum of the AgGaSe2:Co2+, three absorption bands of 1.54, 0.72, and 0.51 eV are observed. It is identified that these impurity absorption peaks are attributed to the electronic transitions between the split energy levels of Co2+ ion with T(d) symmetry sites of the AgGaSe2 host lattice.