Figure 1 (A) Fluorescence spectra of CDs, inset: CDs solution
under (a) daylight and (b) UV; (B) Fluorescence intensity of CDs
solution with different excitations; (C) 3D fluorescence spectrum of CDs
solution; (D) HR-TEM image of CDs; (E) Particle size distribution of CDs
by DLS; (F) UV-vis spectrum of CDs; (G) XRD pattern of CDs; (H) FTIR
spectrum of CDs; (I) XPS survey of CDs.
3.3. Fluorescence stability of
CDs
The optical stability of CDs was investigated by altering the UV
irradiation time, concentrations of sodium chloride and hydrogen
peroxide, temperature, metal ions and organic reagents. As described in
Figure 2A, the fluorescence intensity of CDs remained stable with the
irradiation of UV 365 nm for 120 minutes. Also, their fluorescence was
hardly affected by different concentrations of sodium chloride (Figure
2B), hydrogen peroxide (Figure 2C), and temperature (Figure 2D),
demonstrating that CDs exhibited the favorable photobleaching and
temperature resistance. In contrast, the fluorescence of CDs obvious
deceased in acetic acid rather in other organic solvents (Figure 2E).
Again, the metal ions including Na+,
K+, Cu2+, Mg2+,
Mn2+, Ba2+ and
Ca2+ except Fe2+ scarcely affected
the fluorescence of CDs (Figure 2F), which may be due to the formed
complex between Fe2+ and the functional groups on
their surfaces of CDs.