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.

Anomalous upconversion amplification induced by surface reconstruction in lanthanide sublattices


Upconversion nanocrystals have been extensively investigated for optical imaging and biomedical applications1,2. However, their photoluminescence is strongly attenuated by surface quenching as the nanocrystal size diminishes3. Despite considerable efforts4,5, the quenching mechanism remains poorly understood. Here we report that surface coordination of bidentate picolinic acid molecules to NaGdF4:Yb/Tm nanoparticles enhances four-photon upconversion by 11,000-fold. Mechanistic studies indicate that surface ligand coordination reconstructs orbital hybridization and crystal-field splitting, minimizing the energy difference between the 4f orbitals of surface and inner lanthanide sensitizers. The 4f-orbital energy resonance facilitates energy migration within the ytterbium sublattice, impeding energy diffusion to surface defects and ultimately enhancing energy transfer to the emitters. Moreover, ligand coordination can exert energy-level reconstruction with a ligand–sensitizer separation of over 2 nm. These findings offer insights into the development of highly emissive nanohybrids and provide a platform for constructing optical interrogation systems at single-particle levels.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Multiphoton upconversion enhancement through surface reconstruction.
Fig. 2: Optical investigations of upconversion nanocrystals on surface coordination.
Fig. 3: Ligand-coordination effects on upconversion luminescence enhancement.
Fig. 4: Long-range effect of ligand coordination on upconversion luminescence.

Data availability

All relevant data that support the findings of this work are available from the corresponding author on reasonable request.

Code availability

First-principles calculations were performed using the commercially available Vienna Ab initio Simulation Package. The codes used to calculate the distance between lanthanide ions and ligands are provided in the Supplementary Information.


  1. 1.

    Auzel, F. Upconversion and anti-Stokes processes with f and d ions in solids. Chem. Rev. 104, 139–174 (2004).

    Article  Google Scholar 

  2. 2.

    Zhou, J., Liu, Q., Feng, W., Sun, Y. & Li, F. Upconversion luminescent materials: advances and applications. Chem. Rev. 115, 395–465 (2015).

    Article  Google Scholar 

  3. 3.

    Gargas, D. J. et al. Engineering bright sub-10-nm upconverting nanocrystals for single-molecule imaging. Nat. Nanotechnol. 9, 300–305 (2014).

    ADS  Article  Google Scholar 

  4. 4.

    Rabouw, F. T. et al. Quenching pathways in NaYF4:Er3+,Yb3+ upconversion nanocrystals. ACS Nano 12, 4812–4823 (2018).

    Article  Google Scholar 

  5. 5.

    Mei, S. et al. Networking state of ytterbium ions probing the origin of luminescence quenching and activation in nanocrystals. Adv. Sci. 8, 2003325 (2021).

    Article  Google Scholar 

  6. 6.

    Bünzli, J.-C. G. & Piguet, C. Taking advantage of luminescent lanthanide ions. Chem. Soc. Rev. 34, 1048–1077 (2005).

    Article  Google Scholar 

  7. 7.

    Dong, H., Sun, L. D. & Yan, C. H. Energy transfer in lanthanide upconversion studies for extended optical applications. Chem. Soc. Rev. 44, 1608–1634 (2015).

    Article  Google Scholar 

  8. 8.

    Carneiro Neto, A. N., Moura, R. T. & Malta, O. L. On the mechanisms of nonradiative energy transfer between lanthanide ions: centrosymmetric systems. J. Lumin. 210, 342–347 (2019).

    Article  Google Scholar 

  9. 9.

    Shyichuk, A. et al. Energy transfer upconversion dynamics in YVO4:Yb3+,Er3+. J. Lumin. 170, 560–570 (2016).

    Article  Google Scholar 

  10. 10.

    Wu, S. et al. Non-blinking and photostable upconverted luminescence from single lanthanide-doped nanocrystals. Proc. Natl Acad. Sci. USA 106, 10917–10921 (2009).

    ADS  Article  Google Scholar 

  11. 11.

    Liu, Q. et al. Single upconversion nanoparticle imaging at sub-10 W cm−2 irradiance. Nat. Photonics 12, 548–553 (2018).

    ADS  Article  Google Scholar 

  12. 12.

    Lee, J. et al. Universal process-inert encoding architecture for polymer microparticles. Nat. Mater. 13, 524–529 (2014).

    ADS  Article  Google Scholar 

  13. 13.

    Bettinelli, M., Carlos, L. & Liu, X. Lanthanide-doped upconversion nanoparticles. Phys. Today 68, 38–44 (2015).

    Article  Google Scholar 

  14. 14.

    Chen, X. et al. Confining energy migration in upconversion nanoparticles towards deep ultraviolet lasing. Nat. Commun. 7, 10304 (2016).

    ADS  Article  Google Scholar 

  15. 15.

    Liu, Y. et al. Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy. Nature 543, 229–233 (2017).

    ADS  Article  Google Scholar 

  16. 16.

    Dong, H. et al. Lanthanide nanoparticles: from design toward bioimaging and therapy. Chem. Rev. 115, 10725–10815 (2015).

    Article  Google Scholar 

  17. 17.

    Fan, Y. et al. Lifetime-engineered NIR-II nanoparticles unlock multiplexed in vivo imaging. Nat. Nanotechnol. 13, 941–946 (2018).

    ADS  Article  Google Scholar 

  18. 18.

    Chen, S. et al. Near-infrared deep brain stimulation via upconversion nanoparticle-mediated optogenetics. Science 359, 679–684 (2018).

    ADS  Article  Google Scholar 

  19. 19.

    Chu, H., Zhao, J., Mi, Y., Di, Z. & Li, L. NIR-light-mediated spatially selective triggering of anti-tumor immunity via upconversion nanoparticle-based immunodevices. Nat. Commun. 10, 2839 (2019).

    ADS  Article  Google Scholar 

  20. 20.

    Quintanilla, M., Ren, F., Ma, D. & Vetrone, F. Light management in upconverting nanoparticles: ultrasmall core/shell architectures to tune the emission color. ACS Photonics 1, 662–669 (2014).

    Article  Google Scholar 

  21. 21.

    Zhang, Y. et al. Ultrasmall-superbright neodymium-upconversion nanoparticles via energy migration manipulation and lattice modification: 808 nm-activated drug release. ACS Nano 11, 2846–2857 (2017).

    Article  Google Scholar 

  22. 22.

    Bian, W. et al. Direct identification of surface defects and their influence on the optical characteristics of upconversion nanoparticles. ACS Nano 12, 3623–3628 (2018).

    ADS  Article  Google Scholar 

  23. 23.

    Ma, C. et al. Optimal sensitizer concentration in single upconversion nanocrystals. Nano Lett. 17, 2858–2864 (2017).

    ADS  Article  Google Scholar 

  24. 24.

    Wu, D. M., García-Etxarri, A., Salleo, A. & Dionne, J. A. Plasmon-enhanced upconversion. J. Phys. Chem. Lett. 5, 4020–4031 (2014).

    Article  Google Scholar 

  25. 25.

    Fernandez-Bravo, A. et al. Ultralow-threshold, continuous-wave upconverting lasing from subwavelength plasmons. Nat. Mater. 18, 1172–1176 (2019).

    ADS  Article  Google Scholar 

  26. 26.

    Zhao, J. et al. Single-nanocrystal sensitivity achieved by enhanced upconversion luminescence. Nat. Nanotechnol. 8, 729–734 (2013).

    ADS  Article  Google Scholar 

  27. 27.

    Liang, L. et al. Upconversion amplification through dielectric superlensing modulation. Nat. Commun. 10, 1391 (2019).

    ADS  Article  Google Scholar 

  28. 28.

    Strange, P., Svane, A., Temmerman, W. M., Szotec, Z. & Winter, H. Understanding the valency of rare earths from first-principles theory. Nature 399, 756–758 (1999).

    ADS  Article  Google Scholar 

  29. 29.

    Zhou, J. et al. Activation of the surface dark-layer to enhance upconversion in a thermal field. Nat. Photonics 12, 154–158 (2018).

    ADS  Article  Google Scholar 

  30. 30.

    Blasse, G. Energy migration in rare-earth compounds. Recl. Trav. Chim. Pays Bas 105, 143–149 (1986).

    Article  Google Scholar 

  31. 31.

    Zuo, J. et al. Precisely tailoring upconversion dynamics via energy migration in core–shell nanostructures. Angew. Chem. Int. Ed. 57, 3054–3058 (2018).

    Article  Google Scholar 

  32. 32.

    Chen, X. et al. Energy migration upconversion in Ce(III)-doped heterogeneous core–shell–shell nanoparticles. Small 13, 1701479 (2017).

    Article  Google Scholar 

  33. 33.

    Garfield, D. J. et al. Enrichment of molecular antenna triplets amplifies upconverting nanoparticle emission. Nat. Photonics 12, 402–407 (2018).

    ADS  Article  Google Scholar 

  34. 34.

    Han, S. et al. Lanthanide-doped inorganic nanoparticles turn molecular triplet excitons bright. Nature 587, 594–599 (2020).

    ADS  Article  Google Scholar 

  35. 35.

    Bünzli, J. C. G. On the design of highly luminescent lanthanide complexes. Coord. Chem. Rev. 293–294, 19–47 (2015).

    Article  Google Scholar 

  36. 36.

    Johnson, N. J. J., Korinek, A., Dong, C. & van Veggel, F. C. J. M. Self-focusing by Ostwald ripening: a strategy for layer-by-layer epitaxial growth on upconverting nanocrystals. J. Am. Chem. Soc. 134, 11068–11071 (2012).

    Article  Google Scholar 

  37. 37.

    Kresse, G. & Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6, 15–50 (1996).

    Article  Google Scholar 

Download references


X.L. acknowledges support from the NUS NANONASH Programme (NUHSRO/2020/002/NanoNash/LOA; R143000B43114), the Singapore Ministry of Education (MOE2017-T2-2-110) and the Agency for Science, Technology and Research (A*STAR) (grant no. A1883c0011). H.X. acknowledges support from the National Natural Science Foundation of China (NSFC) (grant no. 92061205) and Young Innovative Team Supporting Projects of Heilongjiang Province.

Author information




H.X., X.Q. and X.L. conceived, designed and supervised the project and led the collaboration efforts. H.X. and S.H. synthesized the nanocrystals and conducted the optical experiments with contributions from R.D., Q.S. and Y.T. Quantum mechanical calculations were conducted by X.Q. Monte Carlo simulations were performed by Y.W. The manuscript was written by H.X., X.Q., S.H. and X.L. All authors participated in the discussion and analysis of the manuscript.

Corresponding authors

Correspondence to Hui Xu, Xian Qin or Xiaogang Liu.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Photonics thanks Marco Bettinelli, Dayong Jin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Materials and methods, Discussion, Schemes 1–3, Figs. 1–26, Tables 1–5 and refs. 1–10.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Xu, H., Han, S., Deng, R. et al. Anomalous upconversion amplification induced by surface reconstruction in lanthanide sublattices. Nat. Photon. 15, 732–737 (2021).

Download citation


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