Magneto-optic studies of rare earth containing sodium silicate glasses and semiconductor quantum dots in glass composites: Nonlinear effects

摘要

Faraday rotation has been measured at room temperature and at magnetic field strengths up to 2.57 T for II-VI type semi-conductor nano-crystals (CdS and CdSe) in the form of quantum dots (QDs) and for rare earth containing sodium silicate glasses. The graph of Faraday rotation versus field strength for all quantum dots showed kinks (abrupt slope changes) which is evidence for a non-linear Faraday effect. Given the inverse linearity seen in dot size versus magnetic field, possible causes such as exciton coulomb interactions were considered as a mechanism for the enhanced Faraday rotation. The rare earth containing glasses also showed a non-linearity in the Faraday rotation as a function of magnetic field strength. However, a single crystal NaCl sample exhibited no kinks up to 2.57 T. Various mechanisms will be put forth and evaluated as to the feasibility of using these processes to explain the observed effects. We consider Landau levels, resonance effects, shape and piezo-electric effects, electron-spin correlation for the quantum dot composites; and intermediate range order (IRO) for the rare earth containing glass matrix itself and try to interpret how each of these mechanisms may or may not have an effect on the Faraday rotation behavior.