Carbon quantum dots (CQDs) are fluorescent carbon nanomaterials with unique optical and structural properties. The detailed stability analysis of CQDs is very much needed for their commercial applications.

This review puts forth the in-depth understanding of the fundamentals of carbon quantum dots(CQDs), recent advancements in the field including a thorough discussion on different roles of CQDs to enhance the performance of solar cells and white-LEDs.

Nitrogen- and sodium-doped carbon quantum dots (CQDs) were synthesized from citric acid monohydrate and urea, using varying concentrations of Ethylenediaminetetraacetic acid disodium salt dehydrate (EDTA) in a bottom-up approach with microwave irradiation. First, a comparative study of synthesis duration and EDTA concentration was conducted. Upon optimization, our results showed that E1-CQD@300sec exhibited the highest absorbance among all EDTA-CQD samples, with absorbance values following this trend: EDTA-CQD@300sec > EDTA-CQD@225sec > EDTA-CQD@165sec for most EDTA concentrations. Additionally, photoluminescence (PL) was found to follow the order: E2-CQD@165sec > E1-CQD@225sec ≈ E1-CQD@300sec. E1-CQD@300sec had a spherical morphology with an approximate size of 13 nm, as observed in high-resolution transmission electron microscopy (HR-TEM). This E1-CQD@300sec sample has a bandgap of 1.95 eV, with a highest occupied molecular orbital (HOMO) of -5.15 eV and a lowest unoccupied molecular orbital (LUMO) of -3.2 eV. X-ray diffraction (XRD) revealed a broad peak at ~ 26.45°, indicating an amorphous structure, which was confirmed by Raman spectroscopy, showing an I _D /I _G ratio of 1.11. FT-IR analysis indicated the presence of nitrogen-based functional groups, such as C-N and N-H, on the surface. With increase in EDTA concentration, the bandgap of EDTA-CQD@300sec increased, reaching a maximum of 2.29 eV for E5-CQD@300sec, with a HOMO of -5.55 eV and a LUMO of -3.26 eV, and other functional groups, such as C ≡ C and C ≡ N, were also detected in the FT-IR spectra. In addition, agglomeration was further increased in the presence of EDTA, possibly due to uncontrolled nucleation, EDTA-CQD complex formation, high EDTA concentration, and insufficient surface coverage by EDTA, as observed through dynamic light scattering (DLS). The thermal stability of ETDA-CQD@300sec also found to decreased from ~ 208°C to 40 °C. Further modifications and optimization is necessary for potential use of synthesized CQDs in the opto-electronic applications.