516
M. Vacha and S. Hirata
years, we have used single-molecule spectroscopy [1, 2] to study the response of
molecular complexes, such as molecular films or π-conjugated polymers, and their
inorganic counterparts, semiconducting quantum dots or halide perovskite nanocrystals, as well as hybrid systems composed of noble metal nanoparticles and organic
dyes [3–18]. Using different modes of electronic excitation, i.e., linear absorption,
localized plasmon enhancement, energy transfer, or charge recombination, we investigate the effect that each excitation mode has on the resulting excited state and its
dynamics. We also attempt to actively manipulate the excited states by external
stimuli such as electric field or external nanoscale pressure induced by a tip of a
scanning probe microscope. In this chapter, we introduce several examples of this
photosynergetic research. In Sect. 30.2, we present our recent work on blinking and
electroluminescence of single perovskite nanocrystals and I-III-IV semiconductor
quantum dots. Section 30.3 introduces the enhancement of energy transfer by localized plasmons of metal nanostructures in hybrid materials. Section 30.4 is devoted
to novel microscopic studies of triplet exciton diffusion in molecular solids.
30.2 Blinking and Electroluminescence of Single Perovskite
Nanocrystals and I-III-IV Semiconductor Quantum
Dots
30.2.1 Electroluminescence and Photoluminescence
of Aggregates of Halide Perovskite Nanocrystals
In recent years, halide perovskites have emerged as a promising alternative material
for light absorption and charge separation in solar cells [19, 20]. Their photophysical
properties, such as large absorption cross section and narrow tunable photoluminescence (PL), have also lead to extensive research aimed at optoelectronic applications,
including light-emitting diodes for displays and lighting, or lasers [21, 22]. Especially, confinement of charges in nanoscale-size structures of different dimensionality
results in drastic improvement of PL quantum yield (QY) and overall brightness, and
perovskite nanocrystals (NCs) have found use as emitters in light-emitting diodes
(LEDs). The advantage of their use is that many aspects of the existing technologies developed for organic LEDs can be applied for dispersions of perovskite NCs.
However, electroluminescence devices prepared from such NCs have long suffered
from low efficiency and there has been no systematic study on the nanoscale origin
of the poor efficiencies.
The light-emitting layer in perovskite LEDs typically consists of several tens of
nanometers of densely packed perovskite NCs. Such emitting layer is sandwiched
between two electrodes and is under external DC bias of several volts. Under such
conditions, the photophysical and electrical processes occurring in the emitting layer
can be very complex. The excitonic and electronic interactions depend on NC sizes
and their distributions, NC distances and orientations, surface and environment of the
M. Vacha and S. Hirata
years, we have used single-molecule spectroscopy [1, 2] to study the response of
molecular complexes, such as molecular films or π-conjugated polymers, and their
inorganic counterparts, semiconducting quantum dots or halide perovskite nanocrystals, as well as hybrid systems composed of noble metal nanoparticles and organic
dyes [3–18]. Using different modes of electronic excitation, i.e., linear absorption,
localized plasmon enhancement, energy transfer, or charge recombination, we investigate the effect that each excitation mode has on the resulting excited state and its
dynamics. We also attempt to actively manipulate the excited states by external
stimuli such as electric field or external nanoscale pressure induced by a tip of a
scanning probe microscope. In this chapter, we introduce several examples of this
photosynergetic research. In Sect. 30.2, we present our recent work on blinking and
electroluminescence of single perovskite nanocrystals and I-III-IV semiconductor
quantum dots. Section 30.3 introduces the enhancement of energy transfer by localized plasmons of metal nanostructures in hybrid materials. Section 30.4 is devoted
to novel microscopic studies of triplet exciton diffusion in molecular solids.
30.2 Blinking and Electroluminescence of Single Perovskite
Nanocrystals and I-III-IV Semiconductor Quantum
Dots
30.2.1 Electroluminescence and Photoluminescence
of Aggregates of Halide Perovskite Nanocrystals
In recent years, halide perovskites have emerged as a promising alternative material
for light absorption and charge separation in solar cells [19, 20]. Their photophysical
properties, such as large absorption cross section and narrow tunable photoluminescence (PL), have also lead to extensive research aimed at optoelectronic applications,
including light-emitting diodes for displays and lighting, or lasers [21, 22]. Especially, confinement of charges in nanoscale-size structures of different dimensionality
results in drastic improvement of PL quantum yield (QY) and overall brightness, and
perovskite nanocrystals (NCs) have found use as emitters in light-emitting diodes
(LEDs). The advantage of their use is that many aspects of the existing technologies developed for organic LEDs can be applied for dispersions of perovskite NCs.
However, electroluminescence devices prepared from such NCs have long suffered
from low efficiency and there has been no systematic study on the nanoscale origin
of the poor efficiencies.
The light-emitting layer in perovskite LEDs typically consists of several tens of
nanometers of densely packed perovskite NCs. Such emitting layer is sandwiched
between two electrodes and is under external DC bias of several volts. Under such
conditions, the photophysical and electrical processes occurring in the emitting layer
can be very complex. The excitonic and electronic interactions depend on NC sizes
and their distributions, NC distances and orientations, surface and environment of the