We have quantum dots with different chemical compositions and surface functionalization. Our quantum dots have uniform size, tunable emission and high quantum yield, as well as good thermal stability. The electronic characteristics and band gap of quantum dots are closely related to its size and shape. By changing the size of our quantum dots, the color of emitted light shifts from blue to near-infrared, which allows the excitation and emission of quantum dots to be highly adjustable, and brings lots of applications for highly sensitive cellular imaging, photovoltaic devices, solar cells, and light emitting devices.