3 years ago

Stochastic Photon Emission from Nonblinking Upconversion Nanoparticles

Stochastic Photon Emission from Nonblinking Upconversion Nanoparticles
Gibok Lee, Eunsang Lee, Kyujin Shin, Minhyuk Jung, Kang Taek Lee, Hohjai Lee, Youngeun Han
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 (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.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b08509

DOI: 10.1021/acs.jpcc.7b08509

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