5.2. Anti-counterfeiting applications
Compared with organic luminescent molecules or inorganic semiconductor
quantum dots, CDs have high luminous stability, creating opportunities
to replace the aforementioned organic materials or quantum dots.
However, their tendency to aggregate by π−π stacking between adjacent
layers, resulting in PL quenching in the solid-state hinders their
widespread application in optoelectronic devices. Such π−π stacking
causes an increase in uncontrolled electroluminescence due to
intermolecular excimer formation, which prevents the formation of pure
emission colors in light-emitting devices. Aggregated luminous CDs
provide a bright prospect for addressing these problems. Park et al.[95] used the functionalization agent to reduce
π−π stacking between adjacent CDs, thus achieving quenching-resistant PL
in the solid-state (Figure 7C). CDs-based white emitting diodes
exhibited efficient down-conversion for white light emission with a
correlated-color temperature of 5612 K and a high color rendering index
of 86.2 at Commission Internationale de l Éclairage (CIE) coordinate of
(0.333, 0.359). In another example,[34] the CIE of
LED based on the solid-state luminous CDs was (0.285, 0.341). Shao et
al. [30] synthesized LEDs with various emission
colors utilizing self-quenching-resistant solid-state fluorescent CDs.
By combining a blue-CDs powder and a self-quenching-resistant
solid-state fluorescent CDs powder, a white light LED with the CIE
coordinate of (0.31, 0.31) was realized. In the other two
examples,[88, 96] the carbon nano ring systems
were used to prevent aggregation-induced PL quenching and to fabricate
high-efficiency LEDs (Figure 7D).