Quantum dots (QDs) have diverse applications, ranging from optics and energy to biomedical. In this study,
carbon quantum dots (CQDs) were synthesized using glucose and tryptophan as precursors using one-step
microwave (MW) and sand bath (SB) thermal methods, and the CQDs exhibit distinct photoluminescence
behaviors. CQD-SB shows enhanced and stable fluorescence despite its amorphous structure, likely due
to prolonged thermal treatment, facilitating the formation of robust surface states and stable reaction
products. Notably, CQD-SB generates a dual emissive bands activated at both shorter and longer
excitation wavelengths (330–390 nm) reveals both core-localized and surface bound group emission.
This stable dual emission suggests a hybrid fluorescence mechanism involving excitation, concentration
and size-dependent effects. However, CQD-MW possesses a partially crystalline structure and exhibits
excitation-dependent dual emission even at higher excitation energies, showing less stability. This
behavior of CQD-MW is due to rapid carbonization and limited passivation owing to instant microwave
heating. Fluorescence staining reveals that CQD-SB offers stronger and more stable blue and green
emission in human buccal and onion epidermal cells, supporting its potential as an efficient bioimaging
probe and alternative to synthetic dyes.