{
  "abstract": "Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized via rapid microwave carbonization of citric acid monohydrate and urea at three CA : Urea mass ratios—2 : 1 (B1-CQD), 1 : 1 (B2-CQD), and 1 : 2 (B3-CQD) to systematically investigate how precursor stoichiometry influences their structural, compositional, and optical properties. XRD and Raman spectroscopy indicated semi-graphitic carbon structures with increasing structural disorder at higher urea content, together with additional crystalline reflections in B3-CQD attributed to reaction by-products. TEM revealed a decrease in particle size with increasing urea content, with B3-CQD exhibiting the smallest (2.95 ± 0.89 nm) and most monodisperse dots. EDX and XPS analyses showed a systematic increase in nitrogen content from 20.5% (B1-CQD) to 31.9% (B3-CQD) by EDX, while total oxygen remained nearly invariant (∼28–30%). The surface-to-bulk nitrogen ratio (SBNR), defined as the ratio of the XPS- to the EDX-derived nitrogen content, increased progressively from 34.1% to 82.4% with increasing urea content, approaching parity between the surface and bulk nitrogen contents; because the XPS sampling depth is comparable to the particle size, the SBNR is presented as a descriptive composition ratio. High-resolution N 1s XPS indicated a redistribution among nitrogen environments, from predominantly pyridinic/amine nitrogen in B1-CQD toward pyrrolic/amide nitrogen in B3-CQD, which XPS alone cannot fully resolve. UV-Vis absorption showed principal maxima at 342.7 nm (B1-CQD), 328.7 nm (B2-CQD), and 328.0 nm (B3-CQD), with an additional shoulder at 273–274 nm in B2-CQD and B3-CQD. Tauc analysis revealed a core-state (π → π*) gap of ∼5.4–5.5 eV together with sub-gap levels between 2.61 and 4.24 eV associated with nitrogen- and oxygen-containing groups. As particle size and nitrogen content vary together in this series, their individual contributions to the optical properties cannot be separated. Excitation-dependent photoluminescence was observed in all samples; under 360 nm excitation, the emission maxima were 438–442 nm, and B3-CQD showed a maximum at 370 nm under 320 nm excitation. Collectively, these findings show that precursor stoichiometry tunes the nitrogen content, surface chemistry, and optical properties of the filtered N-CQD dispersions, which may also contain co-produced molecular species, providing a structure–chemistry–property framework for rational CQD design.",
  "abstract_shown": true,
  "affiliations": [
    "Bhaskaracharya College of Applied Sciences, University of Delhi Delhi India",
    "Department of Electronic Science, University of Delhi South Campus Delhi India",
    "Ramjas College, University of Delhi Delhi India",
    "Indian Institute of Technology Delhi India",
    "Non-Collegiate Women's Education Board, University of Delhi Delhi India"
  ],
  "article_type": "research article",
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Shweta Dua",
      "orcid": "0000-0002-8939-9112"
    },
    {
      "affs": [
        2
      ],
      "name": "Pawan Kumar",
      "orcid": "0000-0001-7510-4283"
    },
    {
      "affs": [
        3
      ],
      "name": "Sakshi Kapoor",
      "orcid": "0009-0004-3616-7512"
    },
    {
      "affs": [
        1
      ],
      "name": "Manoj Kumar Khanna",
      "orcid": "0000-0002-2418-1622"
    },
    {
      "affs": [
        4
      ],
      "name": "Geeta Bhatt",
      "orcid": "0000-0002-1022-0045"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9wpe24fd11zq6.bib",
  "cited_by": 0,
  "doi": "10.1039/d6ra07516a",
  "fulltext_url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13662548/?tool=EBI",
  "id": "9wpe24fd11zq6",
  "issns": [
    "2046-2069"
  ],
  "landing_url": "https://europepmc.org/article/PMC/PMC13662548",
  "language": "eng",
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "heading",
      "Chemistry"
    ],
    [
      "openalex",
      "2505|Carbon and Quantum Dots Applications"
    ]
  ],
  "openalex": "W7221764545",
  "pdf_url": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13662548/pdf/?tool=EBI",
  "pmcid": "PMC13662548",
  "pmid": "42877580",
  "published": "2026-10-14",
  "publisher": "Royal Society of Chemistry",
  "ris": "https://research.draconitic.com/paper/9wpe24fd11zq6.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:20Z",
      "native_id": "PMC:PMC13662548",
      "source": "europepmc",
      "url": "https://europepmc.org/article/PMC/PMC13662548"
    },
    {
      "first_seen": "2026-11-01T12:23:37Z",
      "native_id": "PMC13662548",
      "source": "pmc",
      "url": "https://doi.org/10.1039/d6ra07516a"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2505|Carbon and Quantum Dots Applications",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Tuning carbon quantum dot optics through nitrogen surface chemistry",
  "title_text": "Tuning carbon quantum dot optics through nitrogen surface chemistry",
  "type": "peer-reviewed",
  "updated_at": "2026-11-02T12:20:51Z",
  "url": "https://research.draconitic.com/paper/9wpe24fd11zq6",
  "venue": "RSC advances",
  "versions": []
}