Orange, yellow and blue luminescent carbon dots controlled by surface state for multicolor cellular imaging, light emission and illumination

Three kinds of carbon dots (CDs) with different photoluminescence (PL) (blue, yellow or orange) were synthesized by microwave heating. They display wavelength-independent excitation wavelengths (in the range from 444 to 574nm), similar average particle size (from 3.7 to 4.2nm), and fluorescence lifetimes (from 2.7 to 3.1ns). Color and quantum yields (from 8 to 45% in ethanol) are related to the oxidation degree and the number of N-functional groups on their surface. The CDs are shown to be viable nanoprobes for multicolor imaging of cells. Three composite phosphors were obtained by coating the various CDs on starch particle. The resulting nanomaterials emit solid-state fluorescence with a quantum yield of 16%. They were used to fabricate luminescent blocks and light-emitting diodes with controllable color temperature.