Jorge Luengo

Composition dependence of the energy gap of ZnxMn1 − xIn2Se4 and optical absorption spectroscopy

Composition dependence of the band gap of ZnxMn1 − xIn2Se4 alloys has been studied at 300 K and 77 K for the first time. It was found that for smaller concentrations of Mn the band gap varies linearly with composition and for higher concentrations it shows quadratic dependence. The same trend of dependence was observed for both temperatures. Absorption spectra do reveal the structure located on the higher energy side of the main band gap which has been interpreted on the basis of valence band structure, like, crystal field and spin-orbit interactions.

Chiral optical absorption bands in [ ]CdGa2(1−x)In2xS4 semiconducting compound

Spectroscopic investigation of chiral absorption bands in [ ]CdGa2(1−x)In2xS4 has been carried out at 55K. The origin of these bands is attributed to both the complex structure of the midgap defect states created by inhomogeneity in as-grown samples and the presence of ordered vacancies at cadmium sites. The appearance of chiral bands are associated with dangling bonds in ordered vacancies which help to bring the component of the magnetic dipole moment parallel to the electric dipole moment. The cause for rotation of electric vector of the field is also discussed.

Experimental investigation of intra-shell transitions of Cr2+ in Zn1 − xCrxS

Abstract Quintet-to-triplet transitions of Cr2+ have been detected on the lower energy side of the absorption edge of Zn1 − xCrxS system. We have not only identified the transitions from the ground state 5T2 to 3T1, 3E and 3T2 but also observed spin-orbit splitting of the excited states 3T1 and 3T2. The observed magnitudes of the splitting are very close to the earlier calculated values.

Effect of Mn on defect states in ZnIn2Se4

Abstract ZnIn 2 Se 4 polycrystalline samples were synthesized with small amounts of manganese and their optical absorption spectra examined. It was found that pure material shows the presence of defect states very close to the conduction and valence bands; however, the presence of manganese atoms reduces the density of defects and, at 0.3 at% of Mn, the defect states located very close to the conduction and valence bands are eliminated. The observed results are explained by considering that the Mn atoms tend to occupy the Zn vacancy sites and reduce antisite-induced disorder.

Optical properties of the defect compound CdGa2□S4

Abstract Optical absorption spectra, in the visible (3200–7000) A and in the mid-i.r. region (400–4000) cm −1 , of the defect compound CdGa 2 □S 4 (for both varieties) were examined at 300 K and at 77 K for the first time. From the mid-i.r. spectrum, it has been found that, similar to amorphous materials, there exist high density of states close to the bottom of the conduction band. In the present case they were located at 0.16 eV and at 0.24 eV. In the yellow variety, the absorption spectrum is strongly influenced by the presence of acceptor states, originating from the defect structure.