Publisher Correction: Selective enhancement of optical nonlinearity in two-dimensional organic-inorganic lead iodide perovskites.

In the PDF version of this article, Eq. 5 is missing all elements after the equals sign. The correct version of Eq. 5 is given below. The HTML version of the paper was correct from the time of publication.[Formula: see text].

Selective enhancement of optical nonlinearity in two-dimensional organic-inorganic lead iodide perovskites.

Reducing the dimensionality of three-dimensional hybrid metal halide perovskites can improve their optoelectronic properties. Here, we show that the third-order optical nonlinearity, n 2, of hybrid lead iodide perovskites is enhanced in the two-dimensional Ruddlesden-Popper series, (CH3(CH2)3NH3)2(CH3NH3) n-1Pb n I3n+1 (n = 1-4), where the layer number (n) is engineered for bandgap tuning from E g = 1.60 eV (n = ∞; bulk) to 2.40 eV (n = 1). Despite the unfavorable relation, [Formula: see text], strong quantum confinement causes these two-dimensional perovskites to exhibit four times stronger third harmonic generation at mid-infrared when compared with the three-dimensional counterpart, (CH3NH3)PbI3. Surprisingly, however, the impact of dimensional reduction on two-photon absorption, which is the Kramers-Kronig conjugate of n 2, is rather insignificant as demonstrated by broadband two-photon spectroscopy. The concomitant increase of bandgap and optical nonlinearity is truly remarkable in these novel perovskites, where the former increases the laser-induced damage threshold for high-power nonlinear optical applications.Hybrid metal halide perovskites can exhibit improved optoelectronic properties when their dimensionality is reduced. Here, Saouma et al. study the enhancement of third-order nonlinearities in two-dimensional lead iodide perovskites in the Ruddlesden-Popper series.

Evidence for room temperature electric polarization in RMn(2)O(5) multiferroics.

It is established that the multiferroics RMn(2)O(5) crystallize in the centrosymmetric Pbam space group and that the magnetically induced electric polarization appearing at low temperature is accompanied by a symmetry breaking. However, both our present x-ray study-performed on compounds with R=Pr,Nd,Gd,Tb, and Dy-and first-principles calculations unambiguously rule out this picture. Based on structural refinements, geometry optimization, and physical arguments, we demonstrate in this Letter that the actual space group is likely to be Pm. This turns out to be of crucial importance for RMn(2)O(5) multiferroics since Pm is not centrosymmetric. Ferroelectricity is thus already present at room temperature, and its enhancement at low temperature is a spin-enhanced process. This result is also supported by direct observation of optical second harmonic generation. This fundamental result calls into question the actual theoretical approaches that describe the magnetoelectric coupling in this multiferroic family.

Highly efficient infrared optical nonlinearity of a wide-bandgap chalcogenide Li(2)CdGeS(4).

A quaternary chalcogenide Li(2)CdGeS(4) is an excellent candidate for a nonlinear optical (NLO) material exhibiting wide transparency spanning from its fundamental band edge (3.15 eV) to the terahertz regime (23.5 µm). Strong optical nonlinearity of Li(2)CdGeS(4) has been investigated over a wide spectral range (λ=1.064-3.3 µm) based on second- and third-harmonic generation. The compound has a high damage threshold at λ=1.064 µm because of saturable three-photon absorption, and is phase-matchable for λ>1.5 µm with χ(2) ≃50 pm/V. It also exhibits strong third-order nonlinearity of χ(3) ≃10(5) pm(2)/V(2). Li(2)CdGeS(4) is promising for high-power NLO applications in the broad infrared spectrum.

K4GeP4Se12: a case for phase-change nonlinear optical chalcogenide.

We report on broadband nonlinear optical (NLO) responses from a phase-change chalcogenide compound K(4)GeP(4)Se(12). Its glassy phase exhibits unusual second-harmonic generation (SHG) due to the preservation of local crystallographic order. The SHG efficiency of the glassy form can be boosted by more than 2 orders of magnitude by simple heat treatment. Strong SHG and third-harmonic generation from both glassy and crystalline compounds were characterized over a wide wavelength range of 1.2-4.0 µm. Our results imply that K(4)GeP(4)Se(12) can be utilized for various NLO applications in the mid-infrared spectrum.

One-dimensional long-range plasmonic-photonic structures.

We have fabricated line gratings from periodically etched fused silica on which a thin silver film is deposited that is in turn covered with a silica index-matched fluid. This dielectrically symmetric geometry supports an independent long-range surface plasmon-polariton (LRSPP) and a short-range surface plasmon polariton, and the associated plasmonic band structure has been probed. Coupling to external light is achieved via the patterned grating, and an ultrasharp LRSPP linewidth of 4 nm is observed. The experimental results are compared with finite-difference time-domain simulations.

Metal complexes of N-tosylamidoporphyrin: cis-acetato-N-tosylimido-meso-tetraphenylporphyrinatothallium(III) and trans-acetato-N-tosylimido-meso-tetraphenylporphyrinatogallium(III).

The crystal structures of acetato-N-tosylimido-meso-tetraphenylporphyrinatothallium(III), Tl(N-NTs-tpp)(OAc) (1), and acetato-N-tosylimido-meso-tetraphenylporphyrinatogallium(III), Ga(N-NTs-tpp)(OAc) (2), were determined. The coordination sphere around the Tl3+ ion is a distorted square-based pyramid in which the apical site is occupied by a chelating bidentate OAc- group, whereas for the Ga3+ ion, it is a distorted trigonal bipyramid with O(3), N(3), and N(5) lying in the equatorial plane. The porphyrin ring in the two complexes is distorted to a large extent. For the Tl3+ complex, the pyrrole ring bonded to the NTs ligand lies in a plane with a dihedral angle of 50.8 degrees with respect to the 3N plane, which contains the three pyrrole nitrogens bonded to Tl3+, but for the Ga3+ complex, this angle is found to be only 24.5 degrees. In the former complex, Tl3+ and N(5) are located on the same side at 1.18 and 1.29 A from its 3N plane, but in the latter one, Ga3+ and N(5) are located on different sides at -0.15 and 1.31 A from its 3N plane. The free energy of activation at the coalescence temperature Tc for the intermolecular acetate exchange process in 1 in CD2Cl2 solvent is found to be delta G++171 = 36.0 kJ/mol through 1H NMR temperature-dependent measurements. In the slow-exchange region, the methyl and carbonyl (CO) carbons of the OAc- group in 1 are separately located at delta 18.5 [3J(Tl-13C) = 220 Hz] and 176.3 [2J(Tl-13C) = 205 Hz] at -110 degrees C.