I have several questions regarding the study of carbon-based quantum dots (CQDs).

• Firstly, do they really exhibit the quantum confinement effect? I have read some articles claiming that the quantum confinement effect is not observed in carbon dots, while others state that it only appears in certain forms (carbon nanodots, graphene quantum dots, carbon quantum dots, etc.). The experimental evidence I have reviewed on the size dependence of their energy gap is often confusing. This is because the reported size distributions are usually quite narrow, making it difficult to justify strong confinement effects. Furthermore, shifts in photoluminescence (PL) could also arise from different surface functional groups passivating the dot. From here, my next question arises.
• Can carbon dots be modeled with the same theoretical framework used for traditional semiconductor quantum dots? For example, by considering the free exciton (which is confined and whose properties change with dot size), the exciton bound to surface defects (attributed to surface ligands), etc.? Does it even make sense to talk about the excitonic Bohr radius in carbon dots? I mention this because, although some papers refer to the excitonic Bohr radius, they rarely present a concrete value. Some researchers prefer to model carbon dots from a molecular approach rather than a solid-state one. Also, I might be misunderstanding some concepts, but I thought that any shift should primarily be observed in the absorbance (UV-Vis) spectrum at the band associated with the free exciton, while the PL shift would be a consequence. However, many reports show different PL emissions (with shifts) while their absorbance spectra remain centered at nearly the same positions, with only the appearance of additional bands.
• Regarding the absorption spectra of carbon dots: It is often mentioned that they exhibit characteristic bands in the ultraviolet region (220–360 nm). Typically, two main bands are observed: one in the deeper UV region (250–280 nm), assigned to a π–π* transition of C=C, and another at 300–360 nm, attributed to an n–π* transition of C=O. Additional bands are often associated with doping or with secondary molecules formed during synthesis (that either passivate the dots or remain in solution). A common example is nitrogen doping, which gives rise to an absorption band around 450 nm, attributed to an n–π* transition of C=N. This is the base theory I have understood. However, many articles report different band positions, which is why review papers tend to provide broad intervals instead of specific values. I am unclear why this variability exists. Also, how do researchers determine the exact electronic transition corresponding to each band? In the literature, I often find repeated citations of previous works, and when I trace them back, the discussion of the band assignments is usually vague or implicit. I have also checked absorbance spectra of graphene oxide, which look quite similar. Moreover, the C=C-related band sometimes appears only as a shoulder, while a much more intense absorption band often appears in the deeper UV (200–230 nm). This latter feature is rarely discussed in the literature. As a disclaimer, I am not an organic chemist but a physics student, so I might be misinterpreting some concepts.
• Are polycyclic aromatic hydrocarbons (PAHs) related to carbon dots? From what I have understood, their structures appear quite similar.
• Regarding the synthesis terminology: I find the descriptions of “bottom-up” methods confusing: thermal decomposition, thermolysis, carbonization, or pyrolysis. My conclusion is that they all refer to the same process — heating organic matter at high temperatures (typically 150–250 °C) — but with different names. In my work, I prefer the more general term thermal decomposition. The use of pyrolysis seems especially confusing, since I have learned that pyrolysis strictly refers to decomposition under an inert atmosphere. Yet, some articles are vague about the type of atmosphere, while others specify oxygen-free conditions.
• A final remark: I find it fascinating that carbon dots were only discovered in 2004, almost by accident, and that they can be easily synthesized from a wide range of organic matter, such as biomass or small molecules, by simple heating. It even makes me wonder if we unintentionally produce these nanoparticles during cooking, meaning they might have always been present in our daily lives.

Thank you for taking the time to read this discussion. I would greatly appreciate contributions not only with your expertise but also with personal experiences, especially if you have encountered similar doubts. I am a student currently working on my thesis focused on the fabrication of Grätzel-type solar cells using carbon dots. Suggestions are most welcome.