The relationship between the photoluminescence PL intensity of quantum dots QDs and their size is primarily governed by the quantum confinement effect. As the size of the quantum dots decreases, the energy levels become more discrete, leading to a larger bandgap and a blue shift in the emitted light. This means that smaller quantum dots emit light at shorter wavelengths higher energies while larger quantum dots emit light at longer wavelengths lower energies .The photoluminescence intensity of quantum dots is influenced by several factors, including the size, shape, and composition of the quantum dots, as well as the presence of surface defects and the surrounding environment. In general, smaller quantum dots tend to have higher photoluminescence intensity due to their larger bandgap and stronger quantum confinement effect. However, as the size of the quantum dots decreases, the surface-to-volume ratio increases, which can lead to more surface defects and non-radiative recombination processes that reduce the photoluminescence intensity.The relationship between the photoluminescence intensity and the size of quantum dots can vary for different types of quantum dots, such as those made from different materials or with different shapes. For example, the photoluminescence intensity of CdSe quantum dots is known to increase with decreasing size, while the photoluminescence intensity of InP quantum dots shows a more complex relationship with size, with an initial increase followed by a decrease as the size becomes very small.Additionally, the photoluminescence intensity can be influenced by the presence of a shell around the quantum dot core, such as in core-shell quantum dots e.g., CdSe/ZnS . The shell can passivate surface defects and reduce non-radiative recombination processes, leading to an enhancement of the photoluminescence intensity. The relationship between the photoluminescence intensity and the size of core-shell quantum dots can also vary depending on the thickness and composition of the shell.In summary, the relationship between the photoluminescence intensity of quantum dots and their size is influenced by the quantum confinement effect, surface defects, and the specific properties of the quantum dot material and structure. This relationship can vary for different types of quantum dots, and understanding these variations is important for optimizing the performance of quantum dot-based devices and applications.