Antimony-based metal halide hybrids
have attracted enormous attention
due to the stereoactive 5s2 electron pair that drives intense
triplet broadband emission. However, energy/charge transfer has been
rarely achieved for Sb3+-doped materials. Herein, Sb3+ ions are homogeneously doped into 2D [NH3(CH2)4NH3]CdBr4 perovskite (Cd-PVK)
using a wet-chemical method. Compared to the weak singlet exciton
emission of Cd-PVK at 380 nm, 0.01% Sb3+-doped Cd-PVK exhibits
intense triplet emission located at 640 nm with a near-unity quantum
yield. Further increasing the doping concentration of Sb3+ completely quenches singlet exciton emission of Cd-PVK, concurrently
with enhanced Sb3+ triplet emission. Delayed luminescence
and femtosecond-transient absorption studies suggest that Sb3+ emission originates from exciton transfer (ET) from Cd-PVK host
to Sb3+ dopant, while such ET cannot occur with Pb2+-doped Cd-PVK because of the mismatch of energy levels. In
addition, density function theory calculations indicate that the introduced
Sb3+ likely replace the Cd2+ ions along with
the deprotonation of butanediammonium for charge balance, instead
of generating Cd2+ vacancies. This work provides a deeper
understanding of the ET of Sb3+-doped Cd-PVK and suggests
an effective strategy to achieve efficient triplet Sb3+ emission beyond 0D Cl-based hybrids.
In this work, a new two-dimensional Cd-based (F 2 CHCH 2 NH 3 ) 2 CdBr 4 perovskite (Cd−P) with indirect bandgap and a direct Pb-based (F 2 CHCH 2 NH 3 ) 2 PbBr 4 (Pb−P) are successfully synthesized with isostructural features. Compared to the blueish white light emission of Pb−P, almost no white light can be observed for Cd−P due to the forbidden transition of self-trapped exciton (STE) emission. Interestingly, the white light emission of Cd x Pb 1−x −P (x represents the feed ratio of Cd) is significantly improved with the photoluminescence (PL) quantum yield (QY) raising from <1% to 32.5% by alloying these two isostructural perovskites, which is attributed to the breaking of selection rules for forbidden transitions of STEs with Jahn−Teller like octahedral distortion, as suggested by the results from density functional theory (DFT) calculations and time-resolved spectroscopies. This study demonstrates the intriguing effect of alloying on activating STE emission as an effective approach to control and enhance the optical properties of metal halide perovskites.
Low-dimensional hybrid
lead halide perovskites (LHPs) with broadband
emission (BE) have been developed as promising candidates for single-source
white-light-emitting diodes. However, the underlying origin of such
BE is poorly understood. Herein, dual-emissive [NH3(CH2)8NH3]PbBr4 perovskite microsheets
(PMSs) with good dispersibility are successfully prepared. Besides
the general narrowband emission (NE) originating from free excitons,
BE (∼522 nm) is generated under a Br-poor condition, which
is not observed in the single-crystal sample. Unlike self-trapped
exciton emission, the BE observed in PMSs is experimentally determined
to be related to bromide vacancies (VBr), thereby exhibiting
quasisaturation under high excitation intensity. Femtosecond transient
absorption spectroscopy first shows that the trapping time of the
photogenerated electrons by acceptor-like VBr– is
∼15 ps, slower than that by surface defects (<1 ps). This
study provides new insight into the underlying mechanism of BE and
an effective approach to manipulating the optical properties of 2D
perovskites.
In
this work, four kinds of two-dimensional single-layered F-substituted
ethylammonium lead halide perovskites (LHPs, (F
x
CH3–x
CH2NH3)2PbBr4, x = 0, 1,
2, and 3) are successfully synthesized. The introduction of terminal
F atoms promotes the formation of an inter- and intramolecular hydrogen
bonding network, which has a great impact on the configuration of
F-substituted EA, the interlayer spacing, and distortion of inorganic
layers. Among these four as-prepared samples, (FCH2CH2NH3)2PbBr4 shows the smallest
bandgap (∼2.72 eV) and best photoconductivity because of the
interlayer electronic coupling. Owing to the strong coupling between
excitons and lattice, intense white light emission (quantum yield:
12%) is observed for (F2CHCH2NH3)2PbBr4. Benefiting from the hydrophobic nature of
F–C bonds, (CF3CH2NH3)2PbBr4 presents a greatly improved stability toward
moisture. These findings reveal that constructing inter- and intramolecular
interaction can serve as an effective approach for tuning the broadband
emission and the interlayer conductivity of single-layered LHPs.
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