Optical susceptibilities in singly charged ZnO colloidal quantum dots embedded in different dielectric matrices

Abstract

Within the two-level system approximation, analytical expressions for the linear, third-order nonlinear and intensity-dependent susceptibilities in quantum dots (QDs) embedded in a dielectric matrix are developed by using density matrix equations, considering the local field effect due to the presence of dielectric mismatch. Based on the derived expressions, we perform a comparative study of the optical susceptibilities in singly charged zinc oxide QDs embedded in various dielectric matrices. Three commonly adopted matrices are considered. The electronic structure of the system is numerically calculated. In general, our results indicate that the optical susceptibilities are highly affected by the capped matrices. For example, QDs embedded in the matrix with the largest dielectric constant but the smallest energy band gap exhibit the largest linear and nonlinear optical susceptibilities, while that dispersed in a matrix with the largest energy band gap show the highest threshold energy. It is also found that the third-order nonlinear susceptibility exhibits a stronger dependence on the nature of the capped matrix as compared to its linear counterpart. Finally, we find that the total susceptibility in charged QD immersed in a matrix with a higher dielectric constant is more sensitive to the applied radiation intensity.