ABSTRACT
This chapter discusses low-dimensional systems that are two-dimensional (2D) systems, one-dimensional (1D) systems, and zero-dimensional (0D) systems. 2D systems include layered materials and quantum wells. 1D systems include linear chain-like materials and quantum wires. 0D systems include small microcrystallites and quantum dots. Optical properties of low-dimensional systems are substantially different from those of 3D systems. The most remarkable modification comes from different distributions of energy levels and densities of states originating from the spatial confinement of electrons and holes. Different distributions of energy levels in low-dimensional systems arise from the quantum confinement of electrons and holes. In type-I semiconductor quantum wells, both electrons and holes are confined in the same wells. The luminescence of semiconductor microcrystallites not only depends on the microcrystallites themselves, but also on their surfaces and their surroundings. Many kinds of nanometer-size microcrystallites made by various means behave as quantum dots.
