title: The influence of energy migration on luminescence kinetics parameters in upconversion nanoparticles.
abstract: The mechanism of upconversion at the nanoscale is still under discussion. In this paper, we report on the experimental results of anti-Stokes luminescence kinetics in the upconversion nanoparticles of β-NaYF4: 20%Yb3+; 0.6%Tm3+. The parameters of the luminescence kinetics were found to be unambiguously dependent on the number of excitation quanta n, which are necessary for certain transitions between the energy states of thulium ions. The observed correlation has been explained by means of the long-lasting energy migration between the ytterbium ions. The spread in time between the luminescent maxima of the corresponding thulium transitions not only shows the nonlinear character of upconversion, but also reveals the time scale of energy migration as well. From these, we derive that the conventional Förster formalism applied to the estimation of energy transfer efficiency in UCNP-fluorophore pairs can provide misleading results.
authors.affiliation: Federal Scientific Research Centre 'Crystallography and Photonics' of Russian Academy of Sciences, Leninsky pr. 59, Moscow, 119333, Russia. Moscow Institute of Physics and Technology, Institutsky lane 9, Dolgoprudny, Moscow region, 141700, Russia. Institute for Spectroscopy Russian Academy of Sciences, Fizicheskaya, 5, Troitsk, Moscow, 108840, Russia. EUV-Labs LLC, Moscow, Troitsk, Russia.
authors.forename: Sergey
authors.initials: S
authors.lastname: Alyatkin
authors.forename: Ilya
authors.initials: I
authors.lastname: Asharchuk
authors.forename: Kirill
authors.initials: K
authors.lastname: Khaydukov
authors.forename: Andrey
authors.initials: A
authors.lastname: Nechaev
authors.forename: Oleg
authors.initials: O
authors.lastname: Lebedev
authors.forename: Yuri
authors.initials: Y
authors.lastname: Vainer
authors.forename: Vladimir
authors.initials: V
authors.lastname: Semchishen
authors.forename: Evgeny
authors.initials: E
authors.lastname: Khaydukov