Carbon dots (CDs) are a burgeoning star of luminescent carbon-based nanomaterials with emerging interest for various applications. Luminescence from the sp-conjugated domains in the carbon cores is considered to be the intrinsic bandgap emission of CDs, whereas the relationship between them remains poorly understood. Simultaneously, the solvent relaxation of water molecules will quench the fluorescence of CDs, thus, obtaining strong luminescence from CDs aqueous solutions remains a great challenge. Herein, a facile one-step spatial-confined cross-condensation method that uses a heat-induced self-foaming process in ambient pressure has been developed to synthesize highly luminescent CDs with unprecedented photoluminescence quantum yield (PLQY) over 97.2% in water. The unique precursor-derived cross-arranged perylene skeleton in the cores hinders π–π stacking, while the hydrophobicity of the conjugated units mitigates solvent relaxation by water molecules, resulting in near-unity PLQY in aqueous solutions, enabling this to demonstrate the first optically pumped green lasing emission in the CDs aqueous solution. Moreover, a biomaterial-based white light emitting diode is fabricated using the CDs-stained silks as a fluorescence conversion cover to realize a high luminous efficiency of 60.7 lm W with CIE color coordinate of (0.33, 0.35).