Highly Green Emissive Nitrogen-Doped Carbon Dots with Excellent Thermal Stability for Bioimaging and Solid-State LED.

In this study, nitrogen-doped green emissive carbon dots (N-doped CDs) are synthesized via a convenient one-step solid state reaction method. The N-doped CDs show excitation-dependent fluorescence behavior with a maximum emission of 540 nm. Upon the optimum excitation at 400 nm, the quantum yield (QY) of the green emissive CDs is determined to be 13.4% and 50.3% in deionized water and ethanol, respectively. The higher quantum yield of N-doped CDs in ethanol could be caused by a strong hydrogen-bonding. In addition, the obtained N-doped CDs demonstrate excellent thermal stability, which is supported by the fact that the emission intensity nearly has no change after keeping the sample at 90 °C for 120 min. Moreover, the N-doped CDs exhibit green emission after entering into the HeLa cell membrane, indicating their potential to be used as bioimaging agent. Furthermore, the N-doped CDs are dispersed in PVA matrix for solid state film, where the solid-state quenching  is effectively avoided. A green LED is fabricated by packing the CDs-PVA composite on the top of a 395 nm n-UV-Chip, which provides a potentially healthy green light.