Quantum dots (QDs) are often referred to very tiny man made semiconductor particles whose size are normally no more than 10 nanometers. Their extremely small size renders their optical and electronic properties different from those of bulk materials. A majority of QDs have the ability to emit light of specific wavelengths if excited by light or electricity. According to existing literature, the electronic characteristics of QDs are determine d by their size and shape, which means we can control their emission wavelengths by tuning their size. Typically, smaller QDs (e.g., radius of 2~3 nm) emit shorter wavelengths generating colors such as violet, blue or green. While bigger QDs (e.g., radius of 5~6 nm) emit longer wavelengths generating colors like yellow, orange or red. Their highly tunable optical properties based on their size are fascinating,leading to a variety of research and commercial applications including bioimaging, solar cells, LE Ds, diode lasers, and transistors.