Combinatorial Discovery
of Lanthanide-Doped Nanocrystals
with Spectrally Pure Upconverted Emission
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Abstract
Nanoparticles doped with lanthanide ions exhibit stable
and visible
luminescence under near-infrared excitation via a process known as
upconversion, enabling long-duration, low-background biological imaging.
However, the complex, overlapping emission spectra of lanthanide ions
can hinder the quantitative imaging of samples labeled with multiple
upconverting probes. Here, we use combinatorial screening of multiply
doped NaYF<sub>4</sub> nanocrystals to identify a series of doubly
and triply doped upconverting nanoparticles that exhibit narrow, spectrally
pure emission spectra at various visible wavelengths. We then developed
a comprehensive kinetic model validated by our extensive experimental
data set. Applying this model, we elucidated the energy transfer mechanisms
giving rise to spectrally pure emission. These mechanisms suggest
design rules for electronic level structures that yield robust color
tuning in lanthanide-doped upconverting nanoparticles. The resulting
materials will be useful for background-free multicolor imaging and
tracking of biological processes