In situ synthesis of polychromic up/down-conversion carbon dots/YF3 composites for information encryption and security

Polychromic up/down-conversion emissions in carbon dots (CDs) system play a key role in advanced information encryption and security. However, it is difficult to simultaneously achieve tunable up/down-conversion emissions in CDs system owing to the difficulty in preparation of red down-conversion emission and the poor absorption of CDs to near-infrared excitation sources. Herein, red fluorescence (FL) and room-temperature phosphorescence (RTP) emissions are obtained by establishing energy transfer processes from blue CDs to the Eu3+/Mn2+. Color-tunable upconversion luminescence (UCL) is achieved by in situ preparation process of rare-earth (Er3+/Yb3+, Tm3+/Yb3+, and Tm3+/Er3+) co-doped YF3 upconversion nanoparticles on CDs/boric acid composites. Based on the mold-filling, deposition, handwriting and screen-printing methods, various stable security patterns and characters composed of multicolor emissions of FL, UCL and RTP by switching excitation wavelength and external thermal stimulation, showing great potential for information encryption and security. This work paves the way for the color conversion of FL, RTP and UCL in CDs system and the construction of advanced information encryption and security technologies.