No abstract

A comprehensive study of the photoluminescence dynamics in newly developed CdSe/ZnS quantum dots with alloyed core/shell interfaces is presented. Time-correlated single photon counting is used to measure the decay of exciton luminescence from both the ensemble and individual quantum dots. For decreasing emission wavelength (i.e., for smaller dots), the ensemble data reveal increasing total decay rates with greater variation. This systematic change is expected for emitters with stronger quantum confinement and more influenced by the surface/interface trap states. In experiments performed on single quantum dots, the photoluminescence trajectories exhibit two-state blinking behavior. The distributions of the "off"-state probability density are described by an average power-law exponent of 1.5 6 0.2, while the average decay rate of emission from the threshold-discriminated "on"-states is estimated to be 0.035 6 0.004 ns À1 . We suggest that in core/shell quantum dots with a large bandgap offset, the compositionally graded energy profile at the interface may not be smooth enough to suppress nonradiative Auger recombination and prevent blinking.

We report ferromagnetic resonance (FMR) studies of epitaxial MnO∕GaMnAs bilayers. The FMR data have revealed a distinct unidirectional anisotropy about the [11¯0] axis, which we attribute to exchange biasing of ferromagnetic GaMnAs by the adjacent antiferromagnetic MnO layer. The observed unidirectional anisotropy is surprisingly robust with respect to temperature and changing magnetic field.

Articles you may be interested inInvestigation of superlattices based on ferromagnetic semiconductor GaMnAs by planar Hall effect J. Appl. Phys. 111, 07D310 (2012); 10.1063/1.3678436 Magnetic anisotropy in (Ga,Mn)As grown on vicinal GaAs: Effects of the orientation of microwave magnetic field J. Appl. Phys. 109, 07C301 (2011); 10.1063/1.3535426 Quantitative analysis of the angle dependence of planar Hall effect observed in ferromagnetic GaMnAs film

No abstract

Time-resolved photon counting technique was employed to study dynamics of photoluminescence from the ensemble and single CdSe/ZnS quantum dots with the alloyed core/shell interfaces. The ensemble data revealed enhanced effect of disorder-induced trap states for increasing emission energy, as implied from the changes in the distribution of total decay rates. The emission trajectories collected for single quantum dots showed familiar, two-state blinking pattern. It suggests that in a large-band-offset CdSe/ZnS system, the introduced alloying of the core-to-shell region cannot smooth enough the confinement potential in order to suppress nonradiative Auger recombination and blinking.

No abstract

Electron paramagnetic resonance (EPR) has been investigated in two II1-xMnxVI alloys--Cd1-xMnxSe and Cd1-xMnxS--for a series of high Mn concentrations and at low temperatures T, i.e., under conditions where the spin subsystems in these materials are strongly coupled. We have observed a very significant shift of the resonance field from the EPR position of Mn2+ ions that increases with increasing x and with decreasing T. Furthermore, the use of multiple frequencies has allowed us to attribute the observed shift to an internal field that originates from the spin sublattice within the II1-xMnxVI host.