Achieving Strong Circularly Polarized Luminescence through Cascade Cationic Insertion in Lead-free Hybrid Metal Halides.

Generating circularly polarized luminescence (CPL) with simultaneous high photoluminescence quantum yield (PLQY) and dissymmetry factor (g) is difficult due to usually unmatched electric transition dipole moment (μ) and magnetic transition dipole moment (m) of materials. Herein we tackle this issue by playing a "cascade cationic insertion" trick to achieve strong CPL (with PLQY of ~100 %) in lead-free metal halides with high g values reaching -2.3×10 without using any chiral inducers.

Hierarchical Nanoarchitectonics of Ultrathin 2D Organic Nanosheets for Aqueous Processed Electroluminescent Devices.

Ultrathin 2D organic nanosheets (2DONs) with high mobility have received tremendous attention due to thickness of few molecular layers. However, ultrathin 2DONs with high luminescence efficiency and flexibility simultaneously are rarely reported. Here, the ultrathin 2DONs (thickness: 19 nm) through the modulation of tighter molecular packing (distance: ≈3.

Robust and Swiftly Reversible Thermochromic Behavior of a 2D Perovskite of (CH(CHNH))(CHNH)[PbI] for Smart Window and Photovoltaic Smart Window Applications.

Highly robust, swiftly reversible thermochromic nature of a two-dimensional (2D) perovskite of (PDMA)(CHNH)PbI, nominally prepared as = 2 is found, where PDMA = CH(CHNH). A wide band gap variation from 700 to 430 nm is observed between room temperature and >60 °C under ambient conditions, resulting from moisture absorption and desorption. X-ray diffraction and Fourier-transform infrared spectroscopy are performed to analyze the hydrated and dehydrated states.

Optical Properties of Two-Dimensional Perovskite Films of (CHCHNH)[PbI] and (CHCHNH) (CHNH)[PbI].

The temperature dependence of absorption and photoluminescence (PL) spectroscopies were used to study the optical properties of 2D perovskite films, including n = 1 and 3 of (PEA)(CHNH) [Pb I] (PEA = CH(CH)NH). In (PEA)[PbI] (PEPI), excitons coupling to optical phonons with an average energy of ∼30 meV dominate the photophysics of absorption and PL. (PEA)(CHNH)[PbI] (shortened as PMPI), nominally prepared as n = 3, actually was a mixture of multiple layered perovskites with various n.

Giant Rashba splitting in 2D organic-inorganic halide perovskites measured by transient spectroscopies.

Two-dimensional (2D) layered hybrid organic-inorganic halide perovskite semiconductors form natural "multiple quantum wells" that have strong spin-orbit coupling due to the heavy elements in their building blocks. This may lead to "Rashba splitting" close to the extrema in the electron bands. We have used a plethora of ultrafast transient, nonlinear optical spectroscopies and theoretical calculations to study the primary (excitons) and long-lived (free carriers) photoexcitations in thin films of 2D perovskite, namely, (CHCHNH)PbI.

Temperature-Dependent Electric Field Poling Effects in CHNHPbI Optoelectronic Devices.

Organo-lead halide perovskites show excellent optoelectronic properties; however, the unexpected inconsistency in forward-backward I-V characteristics remains a problem for fabricating solar panels. Here we have investigated the reasons behind this "hysteresis" by following the changes in photocurrent and photoluminescence under electric field poling in transverse CHNHPbI-based devices from 300 to 10 K. We found that the hysteresis disappears at cryogenic temperatures, indicating the "freeze-out" of the ionic diffusion contribution.

Bright single-mode random laser from a concentrated solution of π-conjugated polymers.

Using thin stripe excitation of a 10 ns pulsed laser, we observed robust and bright random laser (RL) emission in high concentrated solutions of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT). In particular, within the proper excitation intensity range, single line RL emission is observed in both solutions, with full width at half-maximum of 0.17 nm and 0.

Exciton versus free carrier photogeneration in organometal trihalide perovskites probed by broadband ultrafast polarization memory dynamics.

We studied the ultrafast transient response of photoexcitations in two hybrid organic-inorganic perovskite films used for high efficiency photovoltaic cells, namely, CH(3)NH(3)PbI(3) and CH(3)NH(3)PbI(1.1)Br(1.9) using polarized broadband pump-probe spectroscopy in the spectral range of 0.

Nonlinear optical transmission of lead phthalocyanine-doped nematic liquid crystal composites for multiscale nonlinear switching from nanosecond to continuous wave.

We have formulated composites of lead (II) tetrakis (4-cumylphenoxy) phthalocyanine (PbTCPc) doped into nematic liquid crystal (LC), 4(')-pentyl-4-biphenylcarbonitrile (5-CB), that has received a 90 degree twisted alignment and investigated the nonlinear transmission properties using both pulsed (Nd:YLF 524 nm, 5 ns) and cw (532 nm) lasers. In the nanosecond regime, this compound is a reverse saturable absorber performing similarly to low-concentration solutions of PbTCPc. Under cw conditions, we observe optically self-activated polarization switching with low threshold input energy.

Time-resolved studies of photoinduced birefringence in azobenzene dye-doped polymer films.

We measured transient photoinduced birefringence (delta n) in various azobenzene dye films by pumping with a nanosecond pulse at 532 nm and probing at 633 nm. The switch-on times for the photoinduced birefringence range from nanoseconds to milliseconds and are systematically related with the lowest optical transition energies for those films. Moreover, our results suggest that the transient photoinduced birefringence measurement is a convenient way to determine the relative energies of pi-pi(*) and n-pi(*) states in azo-based materials.