Lead
halide perovskites provide a test bed for exploring nonlinear
optical properties. Although the underlying centrosymmetric crystal
structure of 3D lead halide perovskites precludes the phenomenon of
second harmonic generation, the third and higher-order harmonic generation
are allowed. In this work, we probe the third harmonic generation
(THG) from CsPbBr3 nanocrystals (NCs) and compare it to
the THG from CsPbBr3 NCs with Ruddlesden–Popper
planar faults (RP-CsPbBr3), formed via postsynthetic fusion-growth.
The THG from CsPbBr3 NCs is negligible compared with that
of RP-CsPbBr3 NCs within a wide range of femtosecond excitation
wavelengths. We further compare the THG from a thin film of RP-CsPbBr3 with that of a single crystal of methylammonium lead bromide
(MAPbBr3). The THG efficiency of RP-CsPbBr3 is
found to be three times greater than that of MAPbBr3. An
effective third-order susceptibility of the order of 10–18 m2 V–2 is obtained for a RP-CsPbBr3 film, opening up the prospect of inorganic halide perovskite
NCs with planar defects for a range of nonlinear optical applications.
Fluorination of donor-acceptor copolymers has been one strategy towards enhancing polymer coplanarity, increasing crystallinity, and improving charge transport mechanisms in organic devices. Herein, we report on the synthesis of thiazole...
Self-assembled L,L-diphenylalanine (FF) nanostructures offer an attractive platform for photonics and nonlinear optics. The nonlinear optical (NLO) coefficients of FF nanotubes depend on the diameter of the tube [S. Khanra et al. Phys. Chem. Chem. Phys. 19(4), 3084–3093 (2017)]. To further enhance the NLO properties of FF, we search for structural modifications. Here, we report on the synthesis of fluorinated FF dipeptides by replacing one ortho-hydrogen atom in each of the phenyl groups of FF by a fluorine atom. Density-functional theoretical calculations yield insights into minimum energy conformers of fluorinated FF (Fl-FF). Fl-FF self-assembles akin to FF into micron-length tubes. The effects of fluorination are evaluated on the piezoelectric response and nonlinear optical properties. The piezoelectric d15 coefficient of Fl-FF is found to be more than 10 times higher than that of FF nanotubes, and the intensity of second harmonic generation (SHG) polarimetry from individual Fl-FF nanotubes is more than 20 times that of individual FF nanotubes. Furthermore, we obtain SHG images to compare the intensities of FF and Fl-FF tubes. This work demonstrates the potential of fluorine substitution in other self-assembled biomimetic peptides for enhancing nonlinear optical response and piezoelectricity.
While
the layered hybrid Ruddlesden-Popper (RP) halide perovskites
have already established themselves as the frontrunners among the
candidates in optoelectronics, their all-inorganic counterparts remain
least explored in the RP-type perovskite family. Herein, we study
and compare the optoelectronic properties of all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) with and without RP planar
faults. We find that the RP-CsPbBr3 PNCs possess both higher
exciton binding energy and longer exciton lifetimes. The former is
ascribed to a quantum confinement effect in the PNCs induced by the
RP faults. The latter is attributed to a spatial electron–hole
separation across the RP faults. A striking difference is found in
the up-conversion photoluminescence response in the two types of CsPbBr3 PNCs. For the first time, all-inorganic RP-CsPbBr3 PNCs are tested in light-emitting devices and shown to significantly
outperform the non-RP CsPbBr3 PNCs.
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