High-resolution optical spectroscopy of nickel ions in II-VI semiconductors: Isotope shifts at theT13(F)⇆3T1(P) andT13(F)⇆3A2(F)Ni2+transitions in CdS and ZnS crystals

Abstract

Extremely narrow fine structures in the absorption, emission, and excitation spectra of the ${\mathrm{Ni}}^{2+}$ transitions ${}_{}{}^3{}_{}{}^{}\mathrm{T}_1^{}{}_{}{}^{}$(F)⇆${\mathrm{}}^3$ ${\mathrm{T}}_1$(P) and ${}_{}{}^3{}_{}{}^{}\mathrm{T}_1^{}{}_{}{}^{}$(F)⇆${\mathrm{}}^3$ ${\mathrm{A}}_2$(F) have been achieved by doping CdS and ZnS crystals with very small concentrations of nickel impurities. The incorporation of up to five different nickel isotopes leads to the appearance of clearly resolved isotope splittings of the lines. For the first time the dependence of such splittings on different transitions, different second neighbors, and on external parameters—such as the magnetic field, uniaxial stress, and temperature—has been measured. An adequate description of the assumed level structure and the isotope effect can be obtained by considering the influence of the local phonon energy and of the Jahn-Teller effect for both the initial and the final states of the transitions considered.