OPTICAL-ABSORPTION AND ELECTRON-SPIN-RESONANCE IN CUALS2NI

Electron spin resonance (ESR) and optical absorption spectra have been studied in Ni-doped CuAlS2 crystals, grown by the chemical vapour tra nsport technique. Absorption spectra show optical transitions between 3d-shell originated orbitals of the Ni2+ ion, as well as charge-transf er transitions Ni3+-->Ni2+ and Ni2+-->Ni+, their intensities being dep endent on the position of the Fermi level in the bandgap of the host c ompound. The ESR results confirm the changes in the relative concentra tions of Ni in different charged states caused by the Fermi level shif t in the band gap, this shift, in its turn, being caused by thermal tr eatments of the crystals in various atmospheres.