Controlling the thermal switching in upconverting nanoparticles through surface chemistry


Photon upconversion taking place in small rare-earth-doped nanoparticles has been recently observed to be thermally modulated in an anomalous manner, showing thermal enhancement of the emission intensity. This effect was proved to be linked to the role of adsorbed water molecules as surface quenchers. The surface capping of the particles has a direct influence on the thermal dynamics of water adsorption and desorption, and therefore on the optical properties. Here, we show that the upconversion intensity of small-size (<25 nm) nanoparticles co-doped with Yb3+ and Er3+ ions, and functionalized with different capping molecules, presents clear irreversibility patterns upon thermal cycling that strongly depend on the chemical nature of the nanoparticle surface. By performing temperature-controlled luminescence measurements we observed the formation of a thermal hysteresis loop, resembling an optical switching phenomenon, whose shape and trajectory depend on the hydrophilicity of the surface. Additionally, an intensity overshoot takes place immediately after turning off the heating source, affecting each radiative transition differently. We performed numerical modelling to understand this effect considering non-radiative energy transfer from the surface defect states to the Er3+ ions. These findings are relevant for the comprehension of nanoparticle-based luminescence and the interplay between the surface and volume effects, and more generally, for applications involving UCNPs such as nanothermometry and bioimaging, and the development of optical encoding systems.




Chemistry, Multidisciplinary; Nanoscience & Nanotechnology; Materials Science, Multidisciplinary; Physics, Applied


Martinez, ED; Garcia-Flores, AF; Carneiro, AN; Brites, CDS; Carlos, LD; Urbano, RR; Rettori, C

nossos autores


This work was supported and performed under the auspices of FAPESP through Grants #2011/19924-2, #2012/04870-7, #2012/05903-6, #2015/21290-2, #2015/21289-4, and #2017/10581-1. E. D. M. was the beneficiary of a post-doctoral FAPESP fellowship #2015/23882-4 during part of the development of this work. R. R. U. acknowledges CNPq Grant No. 309483/2018-2. E. D. M. acknowledges funding from ANPCyT-FONCyT PICT 2017-0307. The research was supported by the LNNano-Brazilian Nanotechnology National Laboratory (CNPEM/MCTI) during the use of the electron microscopy open-access facility. This work was also developed within the scope of the project CICECO - Aveiro Institute of Materials, UIDB/50011/2020, financed by Portuguese funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement. Financial support from the European Union's Horizon 2020 FET Open programme under grant agreement no. 801305 is also acknowledged. This work was initiated at IFGW-UNICAMP, Brazil, continued and finished at the current affiliation of the corresponding author.

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