A.Azhagu Parvathi et al./ Elixir Condensed Matter Phys. 60 (2013) 16407-16419 16407 1.Introduction Present decade is witnessing a tremendous improvement in the study of optical and electro-optical properties in the low dimensional semiconductor systems due to the invention of novel experimental techniques. Nano-semiconductors with the desired sizes are manufactured out of these techniques. Spherical semiconductor nanocrystals with the diameter ranging between 1nm and 5nm are synthesized using some simple experimental methods such as wet chemical approach. Moreover, these low dimensional semiconductor nanostructures depend on the energy spectrum of a confined exciton in order to bring out the exotic behaviour of the physical properties with the effect of quantum confinement. These unique properties are used for biological imaging and sensing and may replace the conventional fluorophores with the multiple fluorescence emission [1]. The quantized energies as well as the motion of the exciton will lead a widening band gap if the radius of the nanocrystal smaller than the exitonic Bohr radius [2,3]. The reports in this emerging field direct us to produce novel materials involving some potential applications especially in non-linear opto-electronic devices for controlling the optical signals in optical computers [4,5]. Semiconductor nanocrystals especially II-VI compound nanoparticles will have a large number of potential applications such as photovoltaic cells and luminescent materials [6,7] due to its tunable band gap if the impurities are introduced with the appropriate proportion. The CdS/Zn x Cd 1-x S quantum dot has a large lattice mismatch between the well and barrier layers. So it is important to include the effect of biaxial strain induced by the lattice mismatch which eliminates the degeneracy of the top of valence band. Spontaneous and piezoelectric polarizations, generating built-in electrostatic field especially in wurtzite heterostructures, determine the quantum states of excitons in a quantum dot. Zn x Cd 1-x S is a direct band gap material, and its band gap varies with the range 2.5 eV- 3.5 eV, a promising candidate for light emitting diodes with visible emissions with the proper introduction of Cd content. Hence it becomes more important to understand the excitonic recombination and the band alignment of CdS /Zn x Cd 1-x S compounds. A larger exciton Interband absorption coefficients in a strained Zn 0.2 Cd 0.8 S/ZnS quantum dot A.Azhagu Parvathi 1 and A.John Peter 2* 1 Department of Physics, VV Vanniaperumal College for Women, Virudhunagar-626 001.India. 2 Department of Physics, Govt.Arts and Science College, Melur-625 106. Madurai, India. ABSTRACT Interband optical absorption coefficients in a strained Zn 0.2 Cd 0.8 S/ZnS quantum dot are discussed theoretically taking into account the internal field induced by the spontaneous and piezoelectric polarizations. The effects of geometrical quantum confinement on the exciton binding energies in Zn x Cd 1-x S/ZnS quantum dot are investigated for various confinement potentials and thereby the interband optical transition energy associated with the photon is brought out. The effects of quantum confinement on the heavy hole exciton are brought out here. We calculate the oscillator strengths for the heavy hole and light hole excitons and the total nonlinear optical absorption coefficients in a Zn 0.2 Cd 0.8 S /ZnS quantum dot with the incident photon energy taking into account the effective mass anisotropy of holes. Our results bring out that the oscillator strength depends on the geometrical confinement, electron and hole wave functions and the interaction between them, and the nonlinear optical absorption coefficient shows larger values for smaller dots. © 2013 Elixir All rights reserved. ARTICLE INFO Article history: Received: 23 May 2013; Received in revised form: 24 June 2013; Accepted: 12 July 2013; Keywords Exciton binding energy, Piezoelectricity and spontaneous polarization, Quantum dot. Elixir Condensed Matter Phys. 60 (2013) 16407-16419 Condensed Matter Physics Available online at www.elixirpublishers.com (Elixir International Journal) Tele: +91 9786141966 E-mail addresses: a.john.peter@gmail.com © 2013 Elixir All rights reserved