Metal-free room-temperature phosphorescent (RTP) materials with changeable colors have attracted great attention in anti-counterfeiting information encryption. Most ultralong-lifetime RTP (URTP) luminophores are traditionally obtained through heavy atom effects via enhancing the spin-orbit coupling efficiency. Here, we report the self-assembly of URTP carbon dots (CDs) using diphenylaminourea as the precursor through a thermal-evaporation assisted covalent-binding approach in the presence of boric acid (BA). The BA-functionalized diphenylaminourea-derived CDs (denoted as D-CDs1.5/BA composites) show a rigid network structure with B-C linkages connected to the surface of the CDs, which can effectively suppress the free vibration of CDs to promote intersystem crossover, finally resulting in an excellent URTP afterglow performance. They feature a low singlet-triplet energy gap and reduced nonradiative attenuation properties. As a result, the D-CDs1.5/BA composites exhibit a bifunctional fluorescence/phosphorescence performance with a high phosphorescence quantum efficiency (12.67%) and an ultra-long green afterglow phosphorescence lifetime of up to 3.66 s. A high-level information encryption and fingerprinting description based on the URTP D-CDs1.5/BA composites were then investigated. This work contributes to the feasible design and preparation of novel URTP CD materials with both ultra-long afterglow and a high phosphorescence efficiency, making them promising candidates for advanced anti-counterfeiting applications.