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Although carbon dots (CDs) have been widely investigated as the fluorescence material, research on room temperature phosphorescence (RTP) CDs is still limited. In this work, diethylenetriaminepentaacetic acid (DTPA) was employed as the raw material to synthesize carbon quantum dots (denoted as CQDs-1) by a hydrothermal method. The resulting CQDs-1 inherited CO groups and N atoms from DTPA, which promoted the formation of triplet excitons under light excitation. On this basis, the CQDs-1 were dispersed in a poly-(vinyl alcohol) (PVA) matrix to prepare CQDs-1-PVA composites that exhibited an optimal emission peak at ∼466 nm and emitted the visible afterglow lasting for 8 s. Moreover, tartaric acid (TA) was combined with DTPA as the raw material to synthesize CQDs-2, which induced the formation of π–π conjugated areas in CQDs. As a result, the emission wavelength was slightly red-shifted, and the duration time of afterglow of the CQDs-2-PVA composite was increased to 9 s. Due to the ultralong-lifetime RTP properties of the CQDs-based composites, their applications in the fields of information encryption and anticounterfeiting have also been investigated. Overall, our work offered a convenient avenue for the synthesis of high-quality RTP CQDs. [ABSTRACT FROM AUTHOR]