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Download fileStochastic Photon Emission from Nonblinking Upconversion Nanoparticles
journal contribution
posted on 2017-09-01, 00:00 authored by Eunsang Lee, Minhyuk Jung, Youngeun Han, Gibok Lee, Kyujin Shin, Hohjai Lee, Kang Taek LeeBecause
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 (NaYF4:Yb3+,Er3+/NaYF4) 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 Er3+ 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.