High-Efficient Excitation-Independent Blue Luminescent Carbon Dots

Blue luminescent carbon dots (CDs) were synthesized by the hydrothermal method. Blue-shifts of the maximum emission wavelength from 480 to 443 nm were observed when the concentration of CD solution decreased. The photoluminescence (PL) spectra of CDs at low concentration showed an excitation-independent behaviour, which is very different from the previous reports. Two different emitting mechanisms might work: the intrinsic luminescence from sp2-carbon networks can be responsible for the shorter wavelength part of emission (excitation-independent) at low concentration and the high polarity of nanosized clusters led to the excitation-dependent behaviour of the longer wavelength part at high concentration of CD solution. The photophysical property and concentration-dependent behaviour of the CDs offered new insights into CDs from the viewpoints of both experiments and mechanisms, which will promote diverse potential applications of CDs in the near future.