Chengqiang Wang

Here, we report the photophysical properties of a nanocomposite composed of CsPbBr3 (or I) quantum dots and a nematic liquid crystal (5CB). The liquid crystal (5CB) acts as a cationic-like spacer that effectively arranges the quantum dots (QDs). Temperature-dependent photoluminescence (PL) was used to investigate the optical properties of QDs/5CB nanocomposite films. The liquid crystal modulates the electron−phonon coupling strength and exciton binding energy of the perovskite, providing an effective means to control the arrangement of perovskite QDs. Notably, thin films of the nanocomposite exhibit unique and intriguing absorption and emission characteristics. We also present data on voltage-driven switching between the anisotropic limits. Furthermore, we propose a tandem device architecture based on stacked red, green, and blue (RGB) LED chips for full-color lighting and display applications. These nanocomposite and device strategies offer a viable pathway toward advanced lighting and white LEDs.

The degree of polarization of the bulk-like S-NRs is higher at room temperature, and S-NRs embedded on Light-emitting diode chips demonstrate promising potential as circularly polarized luminescence emitters.

Hybrid perovskites are well-known to suffer from moisture instability, which leads to surface degradation. Two-dimensional (2D) layered organic-inorganic hybrid perovskites are more environmentally stable than the 3D family. However, we have found a unique moisture-induced crystallization phenomenon in 2D Ruddlesden-Popper perovskite (EOA)₂PbI₄ (EOA = HOCH₂CH₂NH₃⁺). The as-prepared amorphous film undergoes a rapid and irreversible transition to a crystalline hydrated phase, when exposed to a high relative humidity atmosphere (>70% RH). This transformation does not occur under dry conditions and remains stable after thermal treatment above 400 K. Remarkably, the crystallized hydrate exhibits a 2 orders of magnitude increase in electrical resistivity compared to the as-prepared amorphous state, suggesting significantly higher charge carrier concentration in the as-prepared film. To our knowledge, this is the first observation of humidity triggered amorphous to crystalline conversion in a 2D perovskite, providing novel insights into the role of moisture in perovskite phase evolution.

The escalating demand for laser protection in military, industrial, and commercial sectors has intensified the pursuit for advanced optical limiting (OL) materials capable of safeguarding against high-intensity laser threats. Despite the progress, current OL materials are beset with challenges such as low linear transmittance, narrow operational bandwidths, and inadequate response speeds, which hinder their effectiveness in practical applications. In this work, an organometallic hybrid perovskite of 3-(fluoropyrrolidinium)MnCl₃ demonstrated significant reverse saturable absorption properties, with an ultralow starting threshold of 9 mJ/cm² and a substantial third-order nonlinear absorption coefficient of 4.1 × 10^-5 m/W at 532 nm. Combined femtosecond transient absorption spectroscopy and density functional theory (DFT) calculations revealed that the strong nonlinear optical response originates from an excited-state absorption-dominated carrier dynamics process. This work establishes a novel material platform for developing high-sensitivity laser protection devices.

Lead-free CsCu₂I₃ perovskites are promising luminescent materials with strong optical performance and environmental stability, but the fundamental origins of their emission polarization remain unclear, particularly whether the intrinsic polarization of self-trapped excitons (STEs) can be maintained. Here, we systematically present the photophysical properties of high-quality CsCu₂I₃ single crystals. Temperature-dependent photoluminescence reveals broadband emission from STEs with strong electron-phonon coupling (γ_LO ≈ 120 meV) and a negative thermal quenching behavior (activation energy of ∼77.5 meV) due to shallow trap states. Crucially, polarized photoluminescence experiments unambiguously demonstrate that the linear polarization (∼14.3% at 80 K) arises specifically from anisotropic absorption and not intrinsic STE emission polarization. Furthermore, angle-dependent Raman spectroscopy demonstrates strong anisotropy, evidenced by the intensity variation across different polarization directions, consistent with the anisotropic absorption behavior of the material. These findings clarify the photophysical origin of emission anisotropy in CsCu₂I₃ and highlight its potential for polarization-related optoelectronic applications.

CsPbBr3 nanoparticles with averaged size of 14 and 2.1 nm (named as 14 and 2 nmNP, respectively) are synthesized capping with the ligand of dodecylbenzene sulfonic acid (DBSA). Using ultrafast transient absorption spectroscopy, free carriers in 14 nmNP characterize with the slow thermalization (∼0.76 ps) and long carrier cooling time (∼1 ns), which could be due to the phonon bottleneck effect. On the other hand, excitons are major photoexcitations in 2 nmNP, presenting with fast thermalization (<100 fs) and short cooling time (∼50 ps); this effective energy dissipation in 2 nmNPs can be ascribed to the involvement of phonons in DBSA ligands. In both 14 and 2 nmNP, we find that the photoexcitation accumulation leads to an increase in the bandgap that can be understood by the Burstein–Moss band filling effect. These results provide insights into the intrinsic photophysics of CsPbBr3 perovskite nanocrystals with different confinement effects, supplying direct implications for optoelectronic applications.

We have studied four 2D layered perovskites, including OA ₂ PbI ₄ (RP phase), ODAPbI ₄ and BDAPbI ₄ (DJ phase), (GA)MAPbI ₄ (ACI phase), where OA is [(C _m H _{2 m +1} )NH ₃ ]( m = 8), ODA is [NH ₃ (CH ₂ ) _m NH ₃ ]( m = 8), BDA is [NH ₃ (CH ₂ ) _m NH ₃ ]( m = 4), and GA is [C(NH ₂ ) ₃ ]; RP, DJ, and ACI means Ruddlesden–Popper, Dion–Jacobson and alternating cations in the interlayer, respectively. The temperature dependence of absorption and photoluminescence (PL) spectra have been measured. From which the average phonon energy (electron‐phonon interaction strength) is analyzed as around 34 (80), 47 (184), 50 (402), and 63 (758) with the unit of meV for OA ₂ PbI ₄ , ODAPbI _4, BDAPbI ₄ , and (GA)MAPbI ₄ , respectively. Larger phonon energy indicates the involvement of more phonons in organic spacer layer, with the corresponding stronger electron‐phonon interaction. Furthermore, ultrafast transient absorption spectroscopy proves that, when the excitation photon energy is serval hundred meV higher than bandgap, the excitons still are the major photoexcitations in OA ₂ PbI ₄ , but polarons are major one in ODAPbI ₄ , BDAPbI ₄ , and (GA)MAPbI ₄ films, no matter the excitonic transitions dominate the absorption at their band edges. This work proves the organic spacers can regulate electron–phonon interaction then optoelectronic properties in 2D perovskites profoundly, which have implications toward future rational design for relevant devices.

Two‐dimensional (2D) monoelemental antimonene has aroused great research interest since it emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER). Nevertheless, the catalytic efficiency of the reported antimonene catalysts has been limited by their poor conductivity and low‐density of exposed active sites. Herein, the active edge sites engineering is adopted to expose abundant catalytically active edge sites by decreasing the size of antimonene nanosheets to ultrasmall‐sized antimonene nanodots (AMNDs). Meanwhile, the synergy effect of the surface modulation strategy by decorating the base surface of AMNDs using the ionic liquid benefits the mass transfer during the HER process. Impressively, the ionic liquid modified AMNDs (noted as IL‐AMNDs) achieve a low overpotential of 116 mV at the current density of 10 mA cm⁻² and excellent long‐term durability, even superior to many other previously reported 2D catalysts. This work spreads the way out for the development of highly active and efficient hydrogen production catalysts.