Single up-conversion nanocrystal as a local temperature probe of electrically heated silver nanowire.

Luminescence thermometry is a powerful technique for monitoring temperature in a sensitive, remote (through light), and minimally invasive manner. Up to now, many macroscopic and microscopic luminescence temperature probes exploiting different temperature sensing schemes have been investigated, with the majority of the studies using aggregates of nanothermometers. This work presents isolated single up-converting NaYF4:Er3+/Yb3+ nanocrystals as functional temperature indicators operating in a standard confocal microscopy configuration. More specifically, the nanocrystals were used to monitor the temperature of a single silver nanowire, whose temperature was controlled electrically via the Joule process. We demonstrate that individual nanocrystals placed near the nanowire can precisely determine the temperature distribution in its surroundings. These results, which combine nanoscopic heat generation with temperature readout using isolated nanocrystals, represent an essential step for the application of isolated single nanoprobes for luminescence thermometry at the nanoscale.

Probing the Interlayer Exciton Physics in a MoS2/MoSe2/MoS2 van der Waals Heterostructure.

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of interlayer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe2/WSe2 heterostructures. Here we report on the observation of long-lived interlayer exciton emission in a MoS2/MoSe2/MoS2 trilayer van der Waals heterostructure. The interlayer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power, and temperature dependence of the interlayer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long-lived valley polarization of interlayer exciton. Intriguingly, the interlayer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the interlayer exciton emission.