Carbon dot (CD)-based room temperature phosphorescence (RTP) nanomaterials have constituted a research hotspot in multidisciplinary fields. Among the promising RTP CDs, fluorescence-phosphorescence dual emissive CDs (FP-CDs) are currently drawing enormous attention. Herein, highly efficient blue-green FP-CDs were easily prepared by a solvent-free pyrolysis treatment of hydroxyurea. The obtained FP-CDs showed high photoluminescence and phosphorescence quantum yields of 21% and 13%, respectively. Detailed experimental characterization revealed that the efficient dual-emission property is derived from the aromatic carbonyl groups at the edge of FP-CDs. Benefiting from the unique optical performance, FP-CDs exhibited good potential in anticounterfeiting and information encryption. This study offers a new strategy for developing dual-emission fluorescence-phosphorescence nanomaterials.