The zero-dimensional perovskites composed of isolated polyhedrons have unique and distinct physical properties compared with threedimensional perovskites composed of interconnected polyhedrons. Here, we study the photodynamics of the zero-dimensional perovskite-like (C 6 H 22 N 4 Cl 3 )-SnCl 3 single crystals composed of isolated [SnCl 3 ] − tetrahedrons. They exhibit red luminescence with huge Stokes shift (2.49 eV), large spectral broadening (416 meV), and long lifetime (6.9 μs). The experiments in conjunction with the ab initio calculations reveal the special roles of high-and low-frequency phonons in the photodynamics of the (C 6 H 22 N 4 Cl 3 )SnCl 3 crystals. The resonance between the organic-cation-related high-frequency optical phonons and the singlet-totriplet state transition induces strong intersystem crossing and resultant spinforbidden luminescence. The strong electron−tetrahedron-related low-frequency optical-phonon coupling revealed by the low-temperature spectral characterization causes large spectral broadening. The strong lattice relaxation owing to localization of the electronic orbitals along with intersystem crossing accounts for the large Stokes shift.
The low-dimensional cesium bismuth halides are intriguing wide-bandgap semiconductors with fruitful photophysics. However, their photodynamics is rather intricate and remains debated. We study the optical properties of the Cs3Bi2Br9 nanoplatelets (NPLs) by using the combined experimental and first-principles calculation methods. The results indicate that the exhibited dominant blue emission band and weak green band arise from two kinds of shallow color centers. The Cs3Bi2Br9 NPLs exhibit Raman active and inactive vibrational modes that are separately ascribed to the localized lattice waves propagating along the edges and interiors of the quantum well-like bromide–bismuth octahedral frameworks in Cs3Bi2Br9. These findings improve our understanding of the unique photodynamics of these multiple quantum well-like semiconductor nanocrystals.
The lead‐free halide double perovskites have attracted great interest owing to their unique photophysical properties. Among them, the luminescence mechanisms of the Cs2AgInCl6 crystallites are still under debate. A hot‐injection method is developed to synthesize novel hollow and spatially symmetric Cs2AgInCl6 nanoplatelets (NPLs) and study the effect of the cation/octahedron alloying on their photodynamics by using the experimental characterizations in conjunction with the density functional theory calculations. The results reveal that the pure Cs2AgInCl6 NPLs exhibit wide‐band and double‐peaked photoluminescence originating separately from free and self‐trapped excitons. The Ag+/Na+ and In3+/Bi3+ alloying, that is, the partial substitution of the [AgCl6]5− and [InCl6]3− octahedra by [NaCl6]5− and [BiCl6]3− octahedra, leads to crystal symmetry breaking and strongly enhanced exciton localization. As a result, the self‐trapped exciton luminescence becomes predominant in the yielded Cs2AgInCl6:NaBi nanoplatelets, and the quantum yield is highly improved to 10.8%. These results improve the understanding of the role of octahedron alloying in the photophysics of the double perovskite nanocrystals and pave the way for their applications in solid‐state lighting.
Inorganic lead halide perovskites are excellent optoelectronic semiconductors; however, little has been known about the characteristics of their nanowire-based light-emitting devices (LEDs). We study the LEDs employing self-assembled CsPbBr3 nanowires as emission layers. They tend to form crystallographic orientation-consistent laterally fused parallel arrays when self-assembling into the emission layer in the device due to Coulomb attraction between such ionic semiconductors. At high nanowire concentration, the LED emits pure green light, and the carriers transport through Fowler–Nordheim (FN) quantum tunneling and direct injection successively. In contrast, at lower nanowire concentration, the luminescence of the LED shifts gradually from green to white with the increasing bias owing to participation of not only the nanowire layer but also the carrier transport layers in the carrier recombination processes. Meanwhile, its carrier transport experiences successively FN quantum tunneling, direct quantum tunneling, and direct injection with the increasing bias. These results highly improve our understanding of the characteristics of perovskite nanowires-based LEDs.
We investigate theoretically the roles of the intrinsic
point defects
in the photophysics of wide-bandgap multi-quantum-well-structured
Cs3Bi2Br9 based on the Shockley–Read–Hall
statistics and multiphonon recombination theory. The GW plus Bethe–Salpeter equation calculation reveals that there
is a prominent exciton peak below the interband absorption edge, and
it clarifies the experimental debate. The most energetically favorable
native defects possess deep thermodynamic transition levels. The bromide
self-interstitials within the octahedron bilayers exhibit as efficient
carrier trapping centers through the non-radiative multiphonon recombination,
with a lifetime of 184 ns being on the same order of magnitude as
the experimental value. The octahedron bilayer surface bromide self-interstitials
account for the experimentally observed dominant blue luminescence
in Cs3Bi2Br9. These results reveal
that the intrinsic point defects at different sites of the multi-quantum-well-like
octahedron bilayers play different roles in the photodynamics of such
unique layer-structured semiconductors.
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