Tailored Fabrication of Carbon Dot Composites with Full‐Color Ultralong Room‐Temperature Phosphorescence for Multidimensional Encryption

matrix, which effectively stabilizes the triplet excited states of B-CDs. Thus, the composites become phosphorescent over a relatively long period (5-12 s) after the removal of the irradiation source. Meanwhile, the increased particle size and oxidation degree of B-CDs obtained at larger citric acid feeding or higher pyrolysis temperature continuously shift the phosphorescence from blue to red. Due to the formation of multiple luminescence centers, the RTP can also be finely modulated by the excitation wavelength. The resulting B-CD composites with highly tunable long lifetime RTP further allow a variety of distinctive applications in multidimensional encryption handily utilizing space, time, and color variations.