Stochastic Photon Emission from Nonblinking Upconversion Nanoparticles

Abstract

Because of their well-known optical properties, upconversion nanoparticles (UCNPs) are regarded as some of the most promising nanomaterials for bioimaging, biosensors, and solar cells. The nonblinking nature of their upconversion emissions has been a particularly beneficial advantage for live-cell imaging. However, the origin of this unique property has never been seriously investigated. We report, for the first time, the observation of stochastic photon emission (SPEM) in core/shell UCNPs (NaYF 4 :Yb 3+ ,Er 3+ /NaYF 4 ) on the microsecond and nanosecond time scales, even under continuous irradiation at 980 nm. This SPEM was attributed to slow "upconversion cycles". We consider that the conventionally reported, nonblinking nature of UCNP emissions can be attributed to the averaging of SPEMs from multiple Er 3+ ions and the low temporal resolution of previous observation. The off-time distribution, which possesses kinetics information for the upconversion pathways, was well fitted to a single exponential indicating involvement of a single rate-determining step. The distinct behaviors of the green and red emissions confirm their different photophysical pathways.

Beyond Coherent Oxide Heterostructures: Atomic‐Scale Structure of Misfit Dislocations

“…Furthermore, noticeable charge transfer and intermixing at oxide heterointerfaces result in the occurrence of a variety of point defects in conjunction with structural defects, which further convolutes the interface structure. Development of charge transfer ionic potentials for oxides, reactive force‐fields, bond‐valence interatomic potentials, and second‐nearest‐neighbor modified embedded‐atom method are prospective approaches that could address the complex charge transfer and related atomic‐scale processes at semi‐coherent oxide heterointerfaces, further assisting in comprehending the actual atomic and chemical structure of the interface. As recently demonstrated by Uberuaga and co‐workers, albeit for a heterointerface between metal and metal oxide, one promising strategy to investigate the structure of misfit dislocations at oxide heterostructures is to strain the film and the substrate so as to keep the supercell size tractable, while still incorporating the full misfit dislocation structure in the DFT supercell.…”

On the Fly” Characterization of YbIII:ErIII Co-Doped Upconversion Nanoparticle Nonlinear Optical Response from Single-Particle Trajectories

“…For example, complete parameterization of the energy-level shown in Figure 1 based on experimental results will require further spectroscopic studies of all the photophysical processes involved and lead to a better model for UCNPs with improved theoretical understanding of the photophysics. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] For lanthanide-containing coordination complexes and clusters as well as smaller UCNPs, [47,48] the resulting faster diffusion will require new approaches, such as, for example, simulations incorporating ballistic dynamics combined with optical micro-spectroscopy experiments at higher frame rates. Furthermore, in such cases, the spectroscopic-stochastic dynamics may involve emitting quantum states in non-stationary populations, without clear timescale separation between photophysics and Brownian motion as shown here.…”

Femtosecond Laser Induced Luminescence in Hierarchically Structured Nd3+,Yb3+,Er3+ Co-Doped Upconversion Nanoparticles: Light-Matter Interaction Mechanisms from Experiments and Simulations

“…Several recent studies have reported fundamental advances in our understanding of energy transfer mechanisms in UCNPs and core-shell UCNPs [20][21][22][23][24][25][26][27][28][29][30]. However, to the best of our knowledge, this work reports for the first time a comparison between experiments and simulations involving femtosecond and CW-induced upconversion with core-triple shell UCNPs containing with Gd III , Nd III , Yb III , and Er III ions.…”