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-NaYF: 20%Yb; 0.6%Tm. 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.

Excitation Modulation of Upconversion Nanoparticles for Switch-like Control of Ultraviolet Luminescence

“…In particular, we focus on the excitation pulse-width sensitivity of UNP luminescence, which reflects the complexity of the relative rates of processes populating participating excited states. UNPs have shown a unique sensitivity to pulsed excitation, in particular to pulse widths in the microsecond to millisecond range. ,− Ability to manipulate luminescence of UNPs using excitation modulation is a phenomenon we previously observed in the visible luminescence of erbium from the 3 S 3/2 and 4 F 9/2 states wherein the frequency of excitation pulses controlled depopulation pathways . High-frequency, 100 kHz, 980 nm excitation pulses produced a more intense red luminescence over green, whereas lower frequency, 100 Hz, excitation pulses corresponded with a greater ratio of green to red luminescence intensity .…”

High-resolution 3D photopolymerization assisted by upconversion nanoparticles for rapid prototyping applications

“…Figure 1c demonstrates photoluminescence (PL) spectra of UCNPs excited by a CW laser at the wavelength of 975 nm. The PL spectrum of the prepared UCNPs featured five emission bands, which are known to result from the Tm 3+ electronic transitions 27 . In particular, the following narrow luminescent lines in UV bands, corresponding to Tm 3+ transitions 1 I 6 → 3 H 6 (288 nm), 1 I 6 → 3 F 4 (345 nm) and 1 D 2 → 3 H 6 (360 nm), were observable.…”

“…The lanthanide-doped NaYF 4 nanocrystals were synthesized via the coordinate stabilization of yttrium, ytterbium, and thulium metal salts in a solution of oleic acid and octadecene carried out with heating at a rate of 200 °C min −1 up to 320 °C in a Wood’s alloy bath in an oxygen-free atmosphere. The details of UCNP synthesis were described by us elsewhere 27 . The core formed by a nanocrystal of β -NaYF 4 co-doped with the Yb 3+ and Tm 3+ ions in 18% and 0.6% molar ratios, respectively; was coated with an undoped crystal shell of NaYF 4 resulting in a core-shell structure of β -NaYF 4 :Yb 3+ ,Tm 3+ /NaYF 4 .…”

Upconversion Nanoparticles Decorated with Polysialic Acid for Solid Tumors Visualization In Vivo

“…UCNPs with the core/shell structure (NaYF 4 : Yb 3+ /Tm 3+ @NaYF 4 ) with an average size of 90 ± 6 nm were synthesized using the solvothermal method described earlier [ 7 ]. The hydrophobic surface of UCNPs was modified with PSA in two stages.…”