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Exciton-phonon coupling and nonradiative relaxation processes have been investigated in near-infrared (NIR) emitting ternary alloyed mercury cadmium telluride (CdHgTe) quantum dots. Organically capped CdHgTe nanocrystals of sizes varying from 2.5-4.2 nm have been synthesized where emission is in the NIR region of 650-855 nm. Temperature-dependent (15-300 K) photoluminescence (PL) and the decay dynamics of PL at 300 K have been studied to understand the photophysical properties. The PL decay kinetics shows the transition from triexponential to biexponential on increasing the size of the quantom dots (QDs), informing the change in the distribution of the emitting states. The energy gap is found to be following the Varshni relation with a temperature coefficient of 2.1-2.8 x 10(-4) eV K-1. The strength of the electron-phonon coupling, which is reflected in the Huang and Rhys factor S, is found in the range of 1.17-1.68 for QDs with a size of 2.5-4.2 nm. The integrated PL intensity is nearly constant until 50 K, and slowly decreases up to 140 K, beyond which it decreases at a faster rate. The mechanism for PL quenching with temperature is attributed to the presence of nonradiative relaxation channels, where the excited carriers are thermally stimulated to the surface defect/trap states. At temperatures of different region (

We investigate the influence of periodically time-modulated cavity frequency on the generation of atomic squeezed states for a collection of N two-level atoms confined in a non-stationary cavity with a moving mirror. We show that the two-photon character of the field generated from the vacuum state of field plays a significant role in producing the atomic or spin squeezed states. We further show that the maximum amount of persistent atomic squeezing is obtained for the initial cavity field prepared in the vacuum state., Comment: To appear in Journal of Physics B, Atomic, Molecular and Optical Physics, 2015

The Rayleigh–Ritz variational approach is widely used to study confined systems with a Dirichlet boundary condition. To exploit this approach, we first derive a general and a simple expression for the energy functional which takes into account the confinement boundary condition that the wavefunction vanishes on a defined surface. This simple functional allows a straightforward variational optimization of any trial function including a cut-off factor fulfilling the Dirichlet boundary conditions. To illustrate the method, we propose a three-parameter correlated wavefunction for confined two- and three-electron systems located at the centre of an impenetrable spherical cavity. In addition, we also carry out a study on the effect of dimensionality of the confinement by considering a helium atom located on the axis of a cylinder which is confined along the transverse direction but free along the axis of the cylinder resulting in a two-dimensional confinement. An exponential cut-off function is used that ensures the satisfaction of the Dirichlet boundary condition and the cusp conditions related to the regular singularities of the Coulomb field. This function is different from the frequently employed linear and quadratic forms and is suitable for both small and large values of the cavity radius rc. We employ this correlated wavefunction to perform variational calculations of ground-state energies of H− ion, He, and Li atoms. We find that the electron–electron and electron–nucleus interactions are accurately described by a Handy–Jastrow factor. The results show that the electron–electron interaction is almost independent of the radius of confinement rc, whereas the electron–nucleus interaction is strongly dependent on the confinement.

This paper is devoted to the study of variation of linear polarizability and nonlinear hyperpolarizability of a helium atom confined in an impenetrable spherical box with the strength of confinement. The calculation of polarizability and hyperpolarizabilities has been performed within density-functional theory (DFT). The ground-state densities required to carry out calculation of response properties have also been obtained by employing a variational approach within DFT. We find that polarizability decreases monotonically with decreasing confinement radius and interestingly the hyperpolarizability not only decreases but also undergoes a change of sign in the strong confinement regime.

We investigate the effect of unequal masses of Bose and Fermi particles on the dipole collective oscillations of degenerate boson?fermion mixtures. In particular, we study the character and the frequency of the dipole mode by using the variational-sum-rule approach. We find that there exists a critical value of the ratio of boson?fermion mass below and above which the character and the frequency of the dipole mode are significantly different.