The
most attractive aspect of perovskite nanocrystals (NCs) for
optoelectronic applications is their widely tunable emission wavelength,
but it has been quite challenging to tune it without sacrificing the
photoluminescence quantum yield (PLQY). In this work, we report a
facile ligand-optimized ion-exchange (LOIE) method to convert room-temperature
spray-synthesized, perovskite parent NCs that emit a saturated green
color to NCs capable of emitting colors across the entire visible
spectrum. These NCs exhibited exceptionally stable and high PLQYs,
particularly for the pure blue (96%) and red (93%) primary colors
that are indispensable for display applications. Surprisingly, the
blue- and red-emissive NCs obtained using the LOIE method preserved
the cubic shape and cubic phase structure that they inherited from
their parent NCs, while exhibiting high crystallinity and high color-purity.
Together with the parent green-emissive NCs, the obtained blue- and
red-emissive NCs provided a very wide color gamut, corresponding to
a Digital Cinema Initiatives-P3 of 140% or an International Telecommunication
Union Recommendation BT.2020 of 102%. With the superior optical merits
of these LOIE-manipulated NCs, a corresponding color conversion luminescence
device provided a high external quantum efficiency (10.5%) and extremely
high brightness (970 000 cd/m2). This study provides
a valid route toward highly stable, extremely emissive, and panchromatic
perovskite NCs with potential use in a variety of future optoelectronic
applications.
In
recent years, perovskite quantum dots (PQDs) with the incorporation
of transition-metal ions for reducing toxicity and enhancing stability
have been in a research hotspot. However, the PQDs containing transition-metal
ions are quite unstable and display low photoluminescence quantum
yields (PLQYs), owing to the existence of defects. Herein, we have
endeavored to introduce simultaneous cation and anion exchange with
cobalt and chloride ions into the host CH3NH3Pb1–x
Co
x
Br3–2x
Cl2x
PQDs followed by matrix encapsulation via poly(methyl methacrylate)
(PMMA) as a favorable approach to stabilize PQDs with improved PLQY.
We have utilized cobalt chloride as the precursor for doping ions.
The emission wavelength can be regulated from green to cyan color
with the increase in doping concentration without negotiating on color
quality, which is believed to be the modification of band gap and
corresponding electron density estimated from the density functional
theory. A high PLQY of 95% is observed even after the incorporation
of cobalt and chloride ions into host PQDs. We demonstrate white light-emitting
diode (LED) prototypes for backlight applications using a PQDs/PMMA
composite on a blue LED chip, which exhibits excellent stability toward
an ambient and robust atmosphere and provides a wide-color gamut of
124% of the NTSC standard. This research paves a way for the research
community to synthesize highly efficient, color-tunable PQDs for wide-color
backlighting applications.
This paper reports packing-shape
effects of amplified spontaneous
emission (ASE) through orbital polarization dynamics between light-emitting
excitons by stacking perovskite (MAPbBr3) quantum dots
(QDs sized between 10 nm and 14 nm) into rod-like and diamond-like
aggregates. The rod-like packing shows a prolonged photoluminescence
(PL) lifetime (184 ns) with 3 nm red-shifted peak (525 nm) as compared
to the diamond-like packing (PL peak, 522 nm; lifetime, 19 ns). This
indicates that the rod-like packing forms a stronger interaction between
QDs with reduced surface-charged defects, leading to surface-to-inside
property-tuning capability with an ASE. Interestingly, the ASE enabled
by rod-like packing shows an orbit–orbit polarization interaction
between light-emitting excitons, identified by linearly/circularly
polarized pumping conditions. More importantly, the polarization dynamics
is extended to the order of nanoseconds in the rod-like assembly,
determined by the observation that within the ASE lifetime (2.54 ns)
the rotating pumping beam polarization direction largely affects the
coherent interaction between light-emitting excitons.
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