As the QDS size is very smaller, the surface defect density reduces, and the band gap broadens (shows blue shift with respect to the bulk material). Emission color of QDs can be easily tuned by adjusting their size, with smaller QDs emitting at shorter wavelengths (blue) and larger QDs emitting at longer wavelengths (red). i.e., quantum size effect. 

Have narrow emission linewidth, which makes them ideal for use in imaging and sensing applications. This is due to the discrete energy levels that are characteristic of quantum confinement.

High photoluminescence quantum yield, that is a larger proportion of the absorbed photons are emitted as light which are more useful in the development of efficient optoelectronic devices.

Also, have a broad absorption spectrum, which allows them to absorb light over a wide range of wavelengths. This property is suitable for applications such as solar cells, where broad spectral coverage is required.

Size-dependent extinction coefficient (the measure of their ability to absorb light), which is more important for the design of QD-based devices, as it affects the device performance.  Consequently,  quantum dots have an attractive wide range of applications, including biological labeling, light-emitting diodes (LEDs), photovoltaics, and quantum computing.