Carbon dots preserve strong blue emission in both aqueous and solid states and their application in intracellular temperature sensing and white light-emitting diodes

The emission of carbon dots is usually quenched in the solid state, thus limiting their application. Herein, we reported the structure and optical properties of carbon dots that preserve intense blue emission in both aqueous and solid states. Structural analysis indicates the obtained carbon dots are largely functionalized by sodium ion (Na+), which could keep the carbon core from direct contact and inhibit the fluorescence resonance energy transfer, leading the carbon dots still emit even after drying to solid powder. Moreover, in addition to the emission intensity, the luminescence lifetime of the aqueous carbon dots responds linearly to temperature in the range from 20 to 70 degrees C, and is stable at different pH and salinity environments, making them promising optical nanothermometers for probing intracellular temperature via dual mode (emission intensity/lifetime). The applicability of the aqueous carbon dots for intracellular temperature sensing has been demonstrated in living cell studies, while that for the solid carbon dots has been demonstrated by constructing a prototype white LEDs with high color rendering index of 96.