abstract
Luminescence thermal stability is a major figure of merit of lanthanide-doped nanoparticles playing an essential role in determining their potential applications in advanced optics. Unfortunately, considering the intensification of multiple electron-vibration interactions as temperature increases, luminescence thermal quenching of lanthanide-doped materials is generally considered to be inevitable. Recently, the emergence of thermally enhanced upconversion luminescence in lanthanide-doped nanoparticles seemed to challenge this stereotype, and the research on this topic rapidly aroused wide attention. While considerable efforts have been made to explore the origin of this phenomenon, the key mechanism of luminescence enhancement is still under debate. Here, to sort out the context of this intriguing finding, the reported results on this exciting topic are reviewed, and the corresponding enhancement mechanisms as proposed by different researchers are summarized. Detailed analyses are provided to evaluate the contribution of the most believed surface-attached moisture desorption process on the overall luminescence enhancement of lanthanide-doped nanoparticles at elevated temperatures. The impacts of other surface-related processes and shell passivation on the luminescence behaviour of the lanthanide-doped materials are also elaborated. Lack of standardization in the reported data and the absence of important experimental information, which greatly hinders the cross-checking and reanalysis of the results, is emphasized as well. On the foundation of these discussions, it is realized that the thermal-induced luminescence enhancement is a form of recovery process against the strong luminescence quenching in the system, and the enhancement degree is closely associated with the extent of luminescence loss induced by various quenching effects beforehand.
keywords
RADIATIVE DECAY-RATE; RARE-EARTH IONS; PARTICLE-SIZE; ENERGY MIGRATION; LUMINESCENCE ENHANCEMENT; QUANTUM YIELDS; NANOPARTICLES; TEMPERATURE; EXCITATION; SHELL
subject category
Chemistry, Physical; Physics, Atomic, Molecular & Chemical
authors
Shi, R; Martinez, ED; Brites, CDS; Carlos, LD
our authors
Projects
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Nanoparticles - based 2D thermal bioimaging technologies - NanoTBTech (NanoTBTech)
acknowledgements
This work was partially developed under the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by Portuguese funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. Financial support from the project NanoHeatControl, POCI-01-0145-FEDER-031469, funded by FEDER, through POCI and by Portuguese funds (OE), through FCT/MCTES, and by the European Union's Horizon 2020 FET Open program under grant agreements no. 801305 are acknowledged. EDM acknowledges funding from the National Agency for the Promotion of Science and Technology (ANPCyT), through grant PICT 2017-0307. R. S. would like to thank Dr Zijun Wang (Ecole Polytechnique) for valuable discussions.