Interaction between Quantum-Confined Excitons and Lattice in Semiconductor Ultrafine Particles

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In semiconductor ultrafine particles, it is important to look for various size-dependent and surface-sensitive phenomena in order to understand the quantum size effects on the electronic states, lattice vibrations and the mutual interactions. In this research project, we have investigated the optical properties of CuCl quantum dots, in which the exciton translational motion is mainly confined. The following results have been obtained concerning the exciton-lattice interactions in the restricted geometries. 1. Size-dependence of the exciton-lattice interaction has been obtained by monitoring the size- and temperature-dependent homogeneous linewidth of the confined exciton luminescence. The interaction between exciton and acoustic vibration increases with the decrease of the dot size due to the short-range character of the deformation-type interaction. 2. Photofatigue effect which appears as the reduction of the exciton luminescence intensity with the long-term exposure to the laser ligh … More t. The origin of this effect is concluded to be due to the formation of the exciton trapping center as a result of lattice relaxation on the surface. 3. Relation between high density exciton effects and excitonic optical nonlinearities has been invest igated through the observation of the nonlinear changes of excion absorption and luminescence. The optical nonlinearities are mainly caused by the mutual interaction between confined excitons, which increases with increase of the dot radius at least up to 5nm. 4. Matrix effect has been studied through the comparison of the optical properties of quantum-confined excitons in CuCl quantum dots embedded in NaCl matrix with those in borosilicate glass matrix.From the above results, the exciton-lattice interaction is concluded to play important roles in the optical properties of CuCl quantum dots. With the aid of the present results, we can expect to understand more about the new properties of semiconductor quantum dots and their dense aggregation. Less