Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Emissive ZnO–graphene quantum dots for white-light-emitting diodes

Abstract

Hybrid nanostructures combining inorganic materials and graphene are being developed for applications such as fuel cells, batteries, photovoltaics and sensors. However, the absence of a bandgap in graphene has restricted the electrical and optical characteristics of these hybrids, particularly their emissive properties. Here, we use a simple solution method to prepare emissive hybrid quantum dots consisting of a ZnO core wrapped in a shell of single-layer graphene. We then use these quantum dots to make a white-light-emitting diode with a brightness of 798 cd m−2. The strain introduced by curvature opens an electronic bandgap of 250 meV in the graphene, and two additional blue emission peaks are observed in the luminescent spectrum of the quantum dot. Density functional theory calculations reveal that these additional peaks result from a splitting of the lowest unoccupied orbitals of the graphene into three orbitals with distinct energy levels. White emission is achieved by combining the quantum dots with other emissive materials in a multilayer light-emitting diode.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Chemical synthesis process for the ZnO–graphene quasi-quantum dots.
Figure 2: Structural characterization of ZnO–graphene quantum dots.
Figure 3: Optical characterization of ZnO–graphene quantum dots.
Figure 4: Modelling of DOS.
Figure 5: Characterization of ZnO–graphene quantum-dot LEDs.

Similar content being viewed by others

References

  1. Novoselov, K. S. et al. Electric field effect in atomically thin carbon films. Science 306, 666–669 (2004).

    Article  CAS  Google Scholar 

  2. Zhang, Y. B., Tan, Y. M., Stormer, H. L. & Kim, P. Experimental observation of the quantum Hall effect and Berry's phase in graphene. Nature 438, 201–204 (2005).

    Article  CAS  Google Scholar 

  3. Alexander, A. Low-energy theory of disordered graphene. Phys. Rev. Lett. 97, 236802 (2006).

    Article  Google Scholar 

  4. Jannik, C. M. et al. The structure of suspended graphene sheets. Nature 446, 60–63 (2007).

    Article  Google Scholar 

  5. Schedin, F. et al. Detection of individual gas molecules adsorbed on graphene. Nature Mater. 6, 652–655 (2007).

    Article  CAS  Google Scholar 

  6. Son, D. I. et al. Flexible organic bistable devices based on graphene embedded in an insulating poly(methyl methacrylate) polymer layer. Nano Lett. 10, 2441–2447 (2010).

    Article  CAS  Google Scholar 

  7. Sun, X. W., Huang, J. Z., Wang, J. X. & Xu, Z. Inorganic/organic hetero-structure light-emitting diode emitting at 342 nm. Nano Lett. 8, 1219–1223 (2008).

    Article  CAS  Google Scholar 

  8. Cole, J. J., Wang, X., Knuesel, R. J. & Jacobs, H. O. Integration of ZnO microcrystals with tailored dimensions forming light emitting diodes and UV photovoltaic cells. Nano Lett. 8, 1477–1481 (2008).

    Article  CAS  Google Scholar 

  9. Caruge, J. M., Halpert, J. E., Wood, V., Bulović, V. & Bawendi, M. G. Colloidal quantum-dot light-emitting diodes with metal-oxide charge transport layers. Nature Photon. 2, 247–250 (2008).

    Article  CAS  Google Scholar 

  10. Anikeeva, P. O., Halpert, J. E., Bawendi, M. G. & Bulovic, V. Electroluminescence from a mixed red–green–blue colloidal quantum dot monolayer. Nano Lett. 7, 2196–2200 (2007).

    Article  CAS  Google Scholar 

  11. Son, D. I. et al. Bistable organic memory device with gold nanoparticles embedded in a conducting poly(n-vinylcarbazole) colloids hybrid. J. Phys. Chem. C 115, 2341–2348 (2011).

    Article  CAS  Google Scholar 

  12. McAlpine, M. C., Ahmad, H., Wang, D. & Heath, J. R. Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors. Nature Mater. 6, 379–384 (2007).

    Article  CAS  Google Scholar 

  13. Sun, Y. & Rogers, J. A. Inorganic semiconductors for flexible electronics. Adv. Mater. 19, 1897–1916 (2007).

    Article  CAS  Google Scholar 

  14. Terrones, M. et al. Graphene and graphite nanoribbons: morphology, properties, synthesis, defects and applications. Nano Today 5, 351–372 (2010).

    Article  Google Scholar 

  15. Son, D. I. et al. Polymer–ultrathin graphite sheet–polymer composite structured flexible nonvolatile bistable organic memory devices. Nanotechnology 22, 295203 (2011).

    Article  Google Scholar 

  16. Zhang, Y., Tang, Z-R., Fu, X. & Xu, Y-J. TiO2–graphene nanocomposites for gas-phase photocatalytic degradation of volatile aromatic pollutant: is TiO2–graphene truly different from other TiO2–carbon composite materials? ACS Nano 4, 7303–7314 (2010).

    Article  CAS  Google Scholar 

  17. Zhang, M. et al. Fast synthesis of SnO2/graphene composites by reducing graphene oxide with stannous ions. J. Mater. Chem. 21, 1673–1676 (2011).

    Article  CAS  Google Scholar 

  18. Niyogi, S. et al. Solution properties of graphite and graphene. J. Am. Chem. Soc. 128, 7720–7721 (2006).

    Article  CAS  Google Scholar 

  19. Kudin, K. N. et al. Raman spectra of graphite oxide and functionalized graphene sheets. Nano Lett. 8, 36–41 (2008).

    Article  CAS  Google Scholar 

  20. Mohiuddin, T. M. G. et al. Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Grüneisen parameters, and sample orientation. Phys. Rev. B 79, 205433 (2009).

    Article  Google Scholar 

  21. Ni, Z. H. et al. Uniaxial strain on graphene: Raman spectroscopy study and band-gap opening. ACS Nano 2, 2301–2305 (2008).

    Article  CAS  Google Scholar 

  22. Dato, A., Radmilovic, V., Lee, Z. H., Phillips, J. & Frenklach, M. Substrate-free gas-phase synthesis of graphene sheets. Nano Lett. 8, 2012–2016 (2008).

    Article  CAS  Google Scholar 

  23. Son, D. I. et al. Carrier transport in flexible organic bistable devices of ZnO nanoparticles embedded in an insulating poly(methyl methacrylate) polymer layer. Nanotechnology 20, 195203 (2009).

    Article  Google Scholar 

  24. Frisch, M. J. et al. Gaussian 03 (Gaussian, 2003).

    Google Scholar 

  25. Eda, G. et al. Blue photoluminescence from chemically derived graphene oxide. Adv. Mater. 22, 505–509 (2010).

    Article  CAS  Google Scholar 

  26. Saxena, S. et al. Investigation of structural and electronic properties of graphene oxide. Appl. Phys. Lett. 99, 013104 (2011).

    Article  Google Scholar 

  27. Huang, J., Xu, Z. & Yang, Y. Low-work-function surface formed by solution-processed and thermally deposited nanoscale layers of cesium carbonate. Adv. Funct. Mater. 17, 1966–1973 (2007).

    Article  CAS  Google Scholar 

  28. Yang, H. Y., Son, D. I., Kim, T. W., Lee, J. M. & Park, W. I. Enhancement of the photocurrent in ultraviolet photodetectors fabricated utilizing hybrid polymer–ZnO quantum dot nanocomposites due to an embedded graphene layer. Org. Electron. 11, 1313–1317 (2010).

    Article  CAS  Google Scholar 

  29. Wang, F. et al. Gate-variable optical transitions in graphene. Science 320, 206–209 (2008).

    Article  CAS  Google Scholar 

  30. Kumar, B., Gong, H., Chow, S. Y., Tripathy, S. & Hua, Y. Photoluminescence and multiphonon resonant Raman scattering in low-temperature grown ZnO nanostructures. Appl. Phys. Lett. 89, 071922 (2006).

    Article  Google Scholar 

Download references

Acknowledgements

Won-Kook Choi acknowledges financial support from the KIST Future Resource Program (2E22721).

Author information

Authors and Affiliations

Authors

Contributions

D.I.S., B.W.K. and W.K.C. conceived and designed the experiments. D.I.S. and B.W.K. performed the experiment. D.I.S., B.W.K. and W.K.C. interpreted and analysed the data. D.I.S., B.W.K., D.H.P., W.S., B.A. and C-L.L. contributed materials/analysis tools. Y.Y. performed DFT calculations. D.I.S. and W.K.C. prepared the manuscript.

Corresponding author

Correspondence to Won Kook Choi.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 7285 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Son, D., Kwon, B., Park, D. et al. Emissive ZnO–graphene quantum dots for white-light-emitting diodes. Nature Nanotech 7, 465–471 (2012). https://doi.org/10.1038/nnano.2012.71

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nnano.2012.71

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing