In situ optical measurement of the rapid Li intercalation and deintercalation dynamics in colloidal 2D layered TiS2 nanodiscs.

We report the in situ optical measurements of the rapid Li intercalation and deintercalation dynamics in 2-dimensional (2D) layered transition metal dichalcogenide (TMD) with a nanoscale lateral dimension using thin films fabricated with size-controlled colloidal TiS2 nanodiscs. The films exhibiting high optical homogeneity, where the interband absorption changes near-linearly to the amount of intercalated Li, enabled facile optical probing of the intercalation dynamics overcoming the shortcomings of amperometry susceptible to complications from non-Faradaic processes. The time scale of Li intercalation and deintercalation was on the order of seconds in the nanodiscs of ∼100 nm lateral dimension, indicating sufficiently rapid dynamic control of the intercalation-induced material properties with a reduced lateral dimension. The change in the rate and reversibility of the dynamics during the multiple intercalation/deintercalation cycles was also measured, providing a unique window to observe the effect of potential structural changes on the intercalation and deintercalation dynamics in 2D layered TMD structures with a nanoscale lateral dimension.

Suppression of quenching in plasmon-enhanced luminescence via rapid intraparticle energy transfer in doped quantum dots.

We show the suppression of luminescence quenching by metal nanoparticles (MNPs) in the plasmon enhancement of luminescence via fast sensitized energy transfer in Mn-doped quantum dots (QDs). The rapid intraparticle energy transfer between exciton and Mn, occurring on a few picoseconds time scale, separates the absorber (exciton) from the emitter (Mn), whose emission is detuned far from the plasmon of the MNP. The rapid temporal separation of the absorber and emitter combined with the reduced spectral overlap between Mn and plasmonic MNP suppresses the quenching of the luminescence while taking advantage of the plasmon-enhanced excitation. We compared the plasmon enhancement of exciton and Mn luminescence intensities in undoped and doped QDs simultaneously as a function of the distance between MNP and QD layers in a multilayer structure to examine the expected advantage of the reduced quenching in the sensitized luminescence. At the optimum MNP-QD layer distance, Mn luminescence exhibits stronger net enhancement than that of the exciton, which can be explained with a model incorporating fast sensitization along with reduced emitter-MNP spectral overlap. This study demonstrates that materials exhibiting fast sensitized luminescence that is sufficiently red-shifted from that of the sensitizer can be superior to usual luminophores in harvesting plasmon enhancement of luminescence by suppressing quenching.

Ratiometric temperature imaging using environment-insensitive luminescence of Mn-doped core-shell nanocrystals.

We report a ratiometric temperature imaging method based on Mn luminescence from Mn-doped CdS-ZnS nanocrystals (NCs) with controlled doping location, which is designed to exhibit strong temperature dependence of the spectral lineshape while being insensitive to the surrounding chemical environment. Ratiometric thermometry on the Mn luminescence spectrum was performed by using Mn-doped CdS-ZnS core-shell NCs that have a large local lattice strain on the Mn site, which results in the enhanced temperature dependence of the bandwidth and peak position. The Mn luminescence spectral lineshape is highly robust with respect to the change in the polarity, phase and pH of the surrounding medium and aggregation of the NCs, showing great potential in temperature imaging under chemically heterogeneous environment. The temperature sensitivity (ΔIR/IR = 0.5%/K at 293 K, IR = intensity ratio at two different wavelengths) is highly linear in a wide range of temperatures from cryogenic to above-ambient temperatures. We demonstrate the surface temperature imaging of a cryo-cooling device showing a temperature variation of >200 K by imaging the luminescence of the NC film formed by simple spin coating, taking advantage of the environment-insensitive luminescence.