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.

  • Letter
  • Published:

Excitonic luminescence upconversion in a two-dimensional semiconductor

Abstract

Photon upconversion is an elementary light–matter interaction process in which an absorbed photon is re-emitted at higher frequency after extracting energy from the medium. This phenomenon lies at the heart of optical refrigeration in solids1, where upconversion relies on anti-Stokes processes enabled either by rare-earth impurities2 or exciton–phonon coupling3. Here, we demonstrate a luminescence upconversion process from a negatively charged exciton to a neutral exciton resonance in monolayer WSe2, producing spontaneous anti-Stokes emission with an energy gain of 30 meV. Polarization-resolved measurements find this process to be valley selective, unique to monolayer semiconductors4. Since the charged exciton binding energy5 closely matches the 31 meV A1′ optical phonon6,7,8,9, we ascribe the spontaneous excitonic anti-Stokes to doubly resonant Raman scattering, where the incident and outgoing photons are in resonance with the charged and neutral excitons, respectively. In addition, we resolve a charged exciton doublet with a 7 meV splitting, probably induced by exchange interactions, and show that anti-Stokes scattering is efficient only when exciting the doublet peak resonant with the phonon, further confirming the excitonic doubly resonant picture.

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: Upconversion of negatively charged exciton to neutral exciton luminescence.
Figure 2: Gate- and polarization-dependent photoluminescence for excitation above and below the exciton.
Figure 3: Doubly resonant anti-Stokes and temperature-dependent PL.
Figure 4: Negatively charged exciton fine structure and its role in anti-Stokes.

Similar content being viewed by others

References

  1. Pringsheim, P. Bemerkungen über den Unterschied von Lumineszenz-und Temperaturstrahlung. Z. Phys. 57, 739–746 (1929).

    ADS  Google Scholar 

  2. Epstein, R. I. et al. Observation of laser-induced fluorescent cooling of a solid. Nature 377, 500–503 (1995).

    Article  ADS  Google Scholar 

  3. Zhang, J., Li, D., Chen, R. & Xiong, Q. Laser cooling of a semiconductor by 40 kelvin. Nature 493, 504–508 (2013).

    Article  ADS  Google Scholar 

  4. Xiao, D., Liu, G.-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).

    Article  ADS  Google Scholar 

  5. Jones, A. M. et al. Optical generation of excitonic valley coherence in monolayer WSe2 . Nature Nanotech. 8, 634–638 (2013).

    Article  ADS  Google Scholar 

  6. Tonndorf, P. et al. Photoluminescence emission and Raman response of monolayer MoS2, MoSe2, and WSe2 . Opt. Express 21, 4908–4916 (2013).

    Article  ADS  Google Scholar 

  7. Sahin, H. et al. Anomalous Raman spectra and thickness-dependent electronic properties of WSe2 . Phys. Rev. B 87, 165409 (2013).

    Article  ADS  Google Scholar 

  8. Chen, S.-Y., Zheng, C., Fuhrer, M. S. & Yan, J. Helicity resolved Raman scattering of MoS2, MoSe2, WS2 and WSe2 atomic layers. Nano Lett. 15, 2526–2532 (2015).

    Article  ADS  Google Scholar 

  9. Zhang, X. et al. Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material. Chem. Soc. Rev. 44, 2757–2785 (2015).

    Article  Google Scholar 

  10. Cerdeira, F., Anastassakis, E., Kauschke, W. & Cardona, M. Stress-induced doubly resonant Raman scattering in GaAs. Phys. Rev. Lett. 57, 3209–3212 (1986).

    Article  ADS  Google Scholar 

  11. Agulló-Rueda, F., Mendez, E. & Hong, J. Doubly resonant Raman scattering induced by an electric field. Phys. Rev. B 38, 12720–12723 (1988).

    Article  ADS  Google Scholar 

  12. Gubarev, S. I., Ruf, T. & Cardona, M. Doubly resonant Raman scattering in the semimagnetic semiconductor Cd0.95Mn0.05Te. Phys. Rev. B 43, 1551–1554 (1991).

    Article  ADS  Google Scholar 

  13. Kaasbjerg, K., Thygesen, K. S. & Jacobsen, K. W. Phonon-limited mobility in n-type single-layer MoS2 from first principles. Phys. Rev. B 85, 115317 (2012).

    Article  ADS  Google Scholar 

  14. Carvalho, B. R., Malard, L. M., Alves, J. M., Fantini, C. & Pimenta, M. A. Symmetry-dependent exciton-phonon coupling in 2D and bulk MoS2 observed by resonance Raman scattering. Phys. Rev. Lett. 114, 136403 (2015).

    Article  ADS  MathSciNet  Google Scholar 

  15. Qiu, D. Y., Da Jornada, F. H. & Louie, S. G. Optical spectrum of MoS2: Many-body effects and diversity of exciton states. Phys. Rev. Lett. 111, 216805 (2013).

    Article  ADS  Google Scholar 

  16. Ye, Z. et al. Probing excitonic dark states in single-layer tungsten disulphide. Nature 5, 214–218 (2014).

    Article  ADS  Google Scholar 

  17. Chernikov, A. et al. Exciton binding energy and nonhydrogenic Rydberg series in monolayer WS2 . Phys. Rev. Lett. 113, 076802 (2014).

    Article  ADS  Google Scholar 

  18. Zhang, C., Johnson, A., Hsu, C. L., Li, L. J. & Shih, C. K. Direct imaging of band profile in single layer MoS2 on graphite: Quasiparticle energy gap, metallic edge states, and edge band bending. Nano Lett. 14, 2443–2447 (2014).

    Article  ADS  Google Scholar 

  19. He, K. et al. Tightly bound excitons in monolayer WSe2 . Phys. Rev. Lett. 113, 026803 (2014).

    Article  ADS  Google Scholar 

  20. Ugeda, M. M. et al. Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor. Nature Mater. 13, 1091–1095 (2014).

    Article  ADS  Google Scholar 

  21. Wang, G. et al. Giant enhancement of the optical second-harmonic emission of WSe2 monolayers by laser excitation at exciton resonances. Phys. Rev. Lett. 114, 097403 (2015).

    Article  ADS  Google Scholar 

  22. Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarization in monolayer MoS2 by optical helicity. Nature Nanotech. 7, 494–498 (2012).

    Article  ADS  Google Scholar 

  23. Cao, T. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nature Commun. 3, 887 (2012).

    Article  ADS  Google Scholar 

  24. Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarization in MoS2 monolayers by optical pumping. Nature Nanotech. 7, 490–493 (2012).

    Article  ADS  Google Scholar 

  25. Seyler, K. L. et al. Electrical control of second-harmonic generation in a WSe2 monolayer transistor. Nature Nanotech. 10, 407–411 (2015).

    Article  ADS  Google Scholar 

  26. Kumar, N. et al. Exciton–exciton annihilation in MoSe2 monolayers. Phys. Rev. B 89, 125427 (2014).

    Article  ADS  Google Scholar 

  27. Mouri, S. et al. Nonlinear photoluminescence in atomically thin layered WSe2 arising from diffusion-assisted exciton–exciton annihilation. Phys. Rev. B 90, 155449 (2014).

    Article  ADS  Google Scholar 

  28. Wang, G. et al. Double resonant Raman scattering and valley coherence generation in monolayer WSe2 . Phys. Rev .Lett. 115, 117401 (2015).

    Article  ADS  Google Scholar 

  29. Zhao, W. et al. Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2 . Nanoscale 5, 9677–9683 (2013).

    Article  ADS  Google Scholar 

  30. Chakraborty, B. et al. Symmetry-dependent phonon renormalization in monolayer MoS2 transistor. Phys. Rev. B 85, 161403(R) (2012).

    Article  ADS  Google Scholar 

  31. Yu, H., Cui, X., Xu, X. & Yao, W. Valley excitons in two-dimensional semiconductors. Natl Sci. Rev. 2, 57–70 (2014).

    Article  Google Scholar 

  32. Aivazian, G. et al. Magnetic control of valley pseudospin in monolayer WSe2 . Nature Phys. 11, 148–152 (2015).

    Article  ADS  Google Scholar 

  33. Yu, H., Liu, G.-B., Gong, P., Xu, X. & Yao, W. Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides. Nature Commun. 5, 3876 (2014).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank R. Merlin and D. Cobden for helpful discussions. This work is mainly supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (DE-SC0008145 and SC0012509). H.Y. and W.Y. are supported by the Croucher Foundation (Croucher Innovation Award), and the RGC and UGC of Hong Kong (HKU17305914P, HKU9/CRF/13G, AoE/P-04/08). J.Y. and D.G.M. are supported by US DoE, BES, Materials Sciences and Engineering Division. H.D. is supported by Department of Energy under Contract No. DE-SC0014349 and National Science Foundation under Contract No. DMR-1503601. X.X. acknowledges a Cottrell Scholar Award, support from the State of Washington-funded Clean Energy Institute, and support from the Boeing Distinguished Professorship in Physics. Device fabrication was performed at the University of Washington Microfabrication Facility and NSF-funded Nanotech User Facility.

Author information

Authors and Affiliations

Authors

Contributions

X.X. and W.Y. conceived and supervised the experiments; A.M.J. fabricated the devices and performed measurements, assisted by J.R.S.; A.M.J., H.Y., X.X., W.Y. analysed the data with discussion from H.D.; J.Y. and D.G.M. provided and characterized the bulk WSe2; T.T. and K.W. provided BN crystals; A.M.J., X.X., W.Y., H.Y. wrote the paper. All authors discussed the results.

Corresponding authors

Correspondence to Wang Yao or Xiaodong Xu.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 1070 kb)

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Jones, A., Yu, H., Schaibley, J. et al. Excitonic luminescence upconversion in a two-dimensional semiconductor. Nature Phys 12, 323–327 (2016). https://doi.org/10.1038/nphys3604

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nphys3604

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