High-temperature RGB ultralong afterglow carbon dots based on cavity encapsulated by cyclodextrins for anti-counterfeiting and information encryption.

Room temperature phosphorescent (RTP) carbon dots (CDs) have the disadvantages of short lifetime, single wavelength and poor stability. Phosphorescence usually suffers severe thermal decay due to strong non-radiative transitions caused by temperature increasing, limiting the use of CDs. Herein, α-Cyclodextrin provides hydrophobic cavities, so for CDs can be encapsulated into this cavity. OH on cyclodextrin also reacts to generate covalent bonds. Both of them restricts the rotation and vibration of the benzene ring and reduces the non-radiative transitions. Compared to the matrix-limited domain, the cavity encapsulation has a better wrapping effect, while the hydrophobic cavity can better isolate the O2 quenching and stabilize the triplet excitons. Based on the abovementioned considerations, the blue/green/red naked-eye visible afterglows of the obtained RGB(Red-Green-Blue) -CDs lasted for about 16 s, 28 s and 2 s. At the same time, due to the high-temperature resistant cavity structure of cyclodextrins, G-CDs can realize high-temperature phosphorescence for 4 s at 200 °C, better than any of the high-temperature phosphorescent CDs reported to date. This is also the first report of CDs emitting red phosphorescence at 200 °C. The differences in lifetime and wavelength among three RGB afterglow CDs achieve potential applications in anti-counterfeiting and information encryption.