Skip to main content

Thank you for visiting 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.

  • Letter
  • Published:

Green light stimulates terahertz emission from mesocrystal microspheres


The discovery of efficient sources of terahertz radiation has been exploited in imaging applications1, and developing a nanoscale terahertz source could lead to additional applications. High-frequency mechanical vibrations of charged nanostructures can lead to radiative emission, and vibrations at frequencies of hundreds of kilohertz have been observed from a ZnO nanobelt under the influence of an alternating electric field2. Here, we observe mechanical resonance and radiative emission at 0.36 THz from core–shell ZnO mesocrystal microspheres excited by a continuous green-wavelength laser. We find that 0.016% of the incident power is converted into terahertz radiation, which corresponds to a quantum efficiency of 33%, making the ZnO microspheres competitive with existing terahertz-emitting materials1,3. The mechanical resonance and radiation stem from the coherent photo-induced vibration of the hexagonal ZnO nanoplates that make up the microsphere shells. The ZnO microspheres are formed by means of a nonclassical, self-organized crystallization process4,5,6, and represent a straightforward route to terahertz radiation at the nanoscale.

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

Access options

Buy this article

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

Figure 1: FE-SEM images and schematic illustration of the ZnO mesocrystal microspheres.
Figure 2: Vibration spectra of the multi-microsphere samples fabricated with synthesis times of 2.5, 3, 5, 7 and 10 h.
Figure 3: Vibration spectra of single and multi-microsphere samples with different synthesis times.
Figure 4: Experimental setup and terahertz absorption spectra.
Figure 5: Dependence on different parameters of terahertz radiation power for the 10 h microsphere sample.

Similar content being viewed by others


  1. Chan, W. L., Deibel, J. & Mittleman, D. M. Imaging with terahertz radiation. Rep. Prog. Phys. 70, 1325–1379 (2007).

    Article  Google Scholar 

  2. Bai, X. D., Gao, P. X., Wang, Z. L. & Wang, E. G. Dual-mode mechanical resonance of individual ZnO nanobelts. Appl. Phys. Lett. 82, 4806–4808 (2003).

    Article  CAS  Google Scholar 

  3. Siegel, P. Terahertz technology. IEEE Trans. Microw. Theory Tech. 50, 910–928 (2002).

    Article  Google Scholar 

  4. Colfen, H. & Antonietti, M. Mesocrystals: inorganic superstructures made by highly parallel crystallization and controlled alignment. Angew. Chem. Int. Ed. 44, 5576–5591 (2005).

    Article  Google Scholar 

  5. Colfen, H. & Antonietti, M. Mesocrystals and Nonclassical Crystallization (Wiley, 2008).

    Book  Google Scholar 

  6. Liu, Z. et al. Intrinsic dipole-field-driven mesoscale crystallization of core–shell ZnO mesocrystal microspheres. J. Am. Chem. Soc. 131, 9405–9412 (2009).

    Article  CAS  Google Scholar 

  7. Wang, Z. L. & Song, J. Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science 312, 242–246 (2006).

    Article  CAS  Google Scholar 

  8. Wang, Z. L. et al. Semiconducting and piezoelectric oxide nanostructures induced by polar surfaces. Adv. Funct. Mater. 14, 943–956 (2004).

    Article  CAS  Google Scholar 

  9. Özgür, Ü. et al. A comprehensive review of ZnO materials and devices. J. Appl. Phys. 98, 041301 (2005).

    Article  Google Scholar 

  10. Kulkarni, A. J., Zhou, M. & Ke, F. J. Orientation and size dependence of the elastic properties of zinc oxide nanobelts. Nanotechnology 16, 2749–2756 (2005).

    Article  CAS  Google Scholar 

  11. Song, J. H., Wang, X. D., Riedo, E. & Wang, Z. L. Elastic property of vertically aligned nanowires. Nano Lett. 5, 1954–1958 (2005).

    Article  CAS  Google Scholar 

  12. Cao, G. X. & Chen, X. Energy analysis of size-dependent elastic properties of ZnO nanofilms using atomistic simulations. Phys. Rev. B 76, 165407 (2007).

    Article  Google Scholar 

  13. Zhao, M. H., Ye, Z. Z. & Mao, S. X. Photoinduced stiffening in ZnO nanobelts. Phys. Rev. Lett. 102, 045502 (2009).

    Article  CAS  Google Scholar 

  14. Zhang, L. X. & Huang, H. C. Young's moduli of ZnO nanoplates: ab initio determinations. Appl. Phys. Lett. 89, 183111 (2006).

    Article  Google Scholar 

  15. Yang, L. W., Wu, X. L., Huang, G. S., Qiu, T. & Yang, Y. M. In situ synthesis of Mn-doped ZnO multileg nanostructures and Mn-related Raman vibration. J. Appl. Phys. 97, 014308 (2005).

    Article  Google Scholar 

  16. Kobiakov, I. B. Elastic, piezoelectric and dielectric properties of ZnO and CdS single crystals in a wide range of temperatures. Solid State Commun. 35, 305–310 (1980).

    Article  Google Scholar 

  17. Lukosz, W. & Kunz, R. E. Light emission by magnetic and electric dipoles close to a plane interface. I. Total radiated power. J. Opt. Soc. Am. 67, 1607–1615 (1977).

    Article  Google Scholar 

  18. Lukosz, W. & Kunz, R. E. Light emission by magnetic and electric dipoles close to a plane interface. II. Total radiated power. J. Opt. Soc. Am. 67, 1615–1619 (1977).

    Article  Google Scholar 

  19. Fauchet, P. M. et al. Light-emitting porous silicon: materials science, properties, and device applications. IEEE J. Sel. Top. Quantum Electron. 1, 1126–1139 (1995).

    Article  CAS  Google Scholar 

  20. Fan, J. Y. et al. 3C–SiC nanocrystals as fluorescent biological labels. Small 4, 1058–1062 (2008).

    Article  CAS  Google Scholar 

  21. Bruchez, M. Jr, Moronne, M., Gin, P., Weiss, S. & Alivisatos, A. P. Semiconductor nanocrystals as fluorescent biological labels. Science 281, 2013–2016 (1998).

    Article  CAS  Google Scholar 

  22. Wu, X. L., Xiong, S. J., Sun, L. T., Shen, J. C. & Chu, P. K. Low-frequency Raman scattering from nanocrystals caused by coherent excitation of phonons. Small 5, 2823–2826 (2009).

    Article  CAS  Google Scholar 

  23. Courty, A., Mermet, A., Albouy, P. A., Duval, E. & Pileni, M. P. Vibration coherence of self-organized silver nanocrystals in f.c.c. supra-crystals. Nature Mater. 4, 395–398 (2005).

    Article  CAS  Google Scholar 

  24. Zhang, C. H., Jin, B. B., Chen, J., Wu, P. H. & Tonouchi, M. Noncontact evaluation of nondoped InP wafers by terahertz time-domain spectroscopy. J. Opt. Soc. Am. B 26, A1–A5 (2009).

    Article  CAS  Google Scholar 

  25. Ristić, M., Ivanda, M., Popović, S. & Musić, S. Dependence of nanocrystalline SnO2 particle size on synthesis route. J. Non-Cryst. Solids 303, 270–280 (2002).

    Article  Google Scholar 

  26. Tiuri, M. E. Radio astronomy receivers. IEEE Trans. Military Electron. 8, 264–272 (1964).

    Article  Google Scholar 

  27. Yamada, Y., Mitsuishi, A. & Yoshinaga, H. Transmission filters in the far-infrared region. J. Opt. Soc. Am. 52, 17–19 (1962).

    Article  CAS  Google Scholar 

Download references


This work was supported by the National Basic Research Programs of China (grants 2011CB922102, 2007CB936301, 2007CB310404), as well as the National and Jiangsu Natural Science Foundations (grants BK2008020, 60976063, 10874071). Partial support was also provided by the Hong Kong Research Grants Council (RGC) under General Research Funds (GRF) no. CityU 112608) and City University of Hong Kong (Strategic Research Grant (SRG) 7008009).

Author information

Authors and Affiliations



X.L.W. designed the experimental setup, performed the experiments, analysed the data, and co-wrote the manuscript. S.J.X. analysed the data and co-wrote the manuscript. Z.L. and J.C.S. performed the experiments. J.C. and P.H.W. designed the experimental setup and analysed the data. T.H.L. plotted all the figures. P.K.C. analysed the data and co-wrote the manuscript.

Corresponding authors

Correspondence to X. L. Wu or Paul K. Chu.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 366 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Wu, X., Xiong, S., Liu, Z. et al. Green light stimulates terahertz emission from mesocrystal microspheres. Nature Nanotech 6, 103–106 (2011).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


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