Versatile
species have been increasingly recognized as important
components and possible fluorescence origins in carbon dots synthesized
via a bottom-up route. Herein, we use 2,7-naphthalenediol and dimethylformamide
as precursors to synthesize a novel type of carbon dots via an ethanothermal
reaction. Two main luminescent components with entirely different
structures, including molecular fluorophores and carbogenic nanodots,
are independently acquired by column chromatography separation and
dialysis, respectively. Through detailed nuclear magnetic resonance
studies, the chemical structure of molecular fluorophores has been
elucidated as 8-ethoxy-3H-cyclopenta[a]naphthalen-3-one (ECNO), while the carbon dot (C-dot) is characterized
as a carbon core with bound fluorophores. A comparative study between
ECNO and C-dots is systematically conducted in terms of steady- and
transient-state emission spectra, environmental sensitivity, and stability.
ECNO shows a single green and excitation-wavelength-independent emission,
but it is highly sensitive to the solution pH and solvent polarity.
As the carbogenic counterpart, C-dots show dual emission comprising
a blue broad and a yellow narrow-band emission. Besides, C-dots exhibit
higher photo- and thermal stability than ECNO. The state of fluorophores
(unbound state vs bound state) causes these dramatic differences in
the optical behaviors between ECNO and C-dots. By virtue of their
distinctive properties, ECNO can be used as a fluorescent filler to
fabricate smart polymer composites and anti-counterfeiting inks, while
C-dots find applications as phosphors in white-light emitting diodes.
Lead
halide perovskite quantum dots (PQDs) have recently been proposed
as scalable and color-tunable single emitters, but their slow spontaneous
emission (1–10 ns) creates a mismatch with high-speed nanophotonic
devices. Here, we demonstrate Purcell enhanced emission rate in hybrid
structure of PQDs coupled to plasmonic crystal at room temperature.
A series of planar devices are produced in large scale via chemistry
assembly using colloidal PQDs, Ag nanocubes, and polyvinylpyrrolidone
(PVP) as building blocks. By varying the PVP spacer thickness as well
as Ag nanocube surface density, a tunable photoluminescence enhancement
is realized in both steady and time-resolved measurements. We show
a 3.5-fold enhancement in the total fluorescence intensity and simultaneously
an increase in the emission rate of a factor of 4.5. Finally, a proof-of-concept
tag using PVP spacer encoded inks is demonstrated, providing a promising
approach for information security based on Purcell-enhanced emission.
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