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Perovskites have emerged as a new family member of saturable absorbers (SAs) to generate high energy and ultrashort laser pulses due to their unique optoelectronic properties, structural and chemical diversity. However, the toxicity of lead-based perovskites as well as their chemical instability constrains the practical implementations of the materials. In this work, we created one alternative lead-free and stable "elpasolite" double perovskite of Cs4CuSb2Cl12, which demonstrated highly saturated absorption extending to the near-infrared (NIR) spectral region with a large βeff value of −6.8 × 10−7 m W−1 at 1064 nm superior to previously reported perovskite materials. Femtosecond transient absorption spectroscopy provides an overall picture of charge carrier dynamics of the perovskite crystals accounting for their strong nonlinear saturation absorption. The as-prepared Cs4CuSb2Cl12 crystal acted as an efficient saturable absorber for Q-switched mode-locking an Yb-doped fiber laser. The ∼1 μm NIR laser modulation with high pulse-energy operation and low saturation power demonstrates the great potential of the new perovskite for integration into lasers, modulators and other photonic devices. [ABSTRACT FROM AUTHOR]

Photocatalytic conversion of CO2 in the atmosphere to fuels and value-added chemicals is a promising artificial carbon cycle to combat the global climate crisis, the accomplishment of which however is strongly reliant on efficient catalysts, i.e., with high selectivity, conversion rate, and robustness. In this work, we provide a solution involving the fabrication of a lead-free perovskite Cs3Bi2Br9/MOF 525 Co structure, where narrow band Cs3Bi2Br9 QDs for efficient light trapping and selective CO2 adsorption, coupled with MOF to form a Cs3Bi2Br9/MOF 525 Co type-II heterojunction for efficient electron–hole separation. In this way, three crucial steps, comprising light absorption, carrier transportation, and highly selective surface catalysis, were fully taken into account and the photocatalyst showed a high CO selectivity of 99.5% and an outstanding electron consumption rate of 124.8 μmol g−1 h−1 (61.2 μmol g−1 h−1 for CO, and 0.3 μmol g−1 h−1 for CH4) superior to previous reports. Femtosecond transient absorption measurements disclosed an ultrafast electron transfer of 136 ps from Cs3Bi2Br9 to MOF 525 Co within the heterojunction, enabling efficient charge separation with a long carrier life time over the ns time scale; further, in situ infrared measurements unraveled the stronger CO2 adsorption, efficient conversion to *COOH intermediates, and prompt CO desorption of the photocatalyst. The present work thus elucidated the underlying mechanism accounting for the high product selectivity, providing guidelines for the design of efficient catalysts from the perspective of dynamics and surface reaction activity. [ABSTRACT FROM AUTHOR]

Ultrathin two-dimensional (2D) metal oxides have recently emerged as members of the 2D family with broad use in the catalytic field and energy storage techniques. However, investigations on their optoelectronic properties, nonlinear optical properties in particular, remain largely elusive. Defect (site) engineering had been a powerful tool to tailor semiconductor band gaps for their catalytic use, while, herein, it was carried out to expand the third-order nonlinear response of ultrathin 2D transition-metal oxide WO3 to the infrared region. By engineering the oxygen vacancy, WO3 demonstrated an indirect band gap adjustable from 2.33 eV (WO3) to 1.54 eV (D-WO3) with enhanced nonlinear saturable absorption extending from the visible to the near-infrared range, which have promising use in mode-locking, laser beam shaping, and ultrafast photonics. Transient absorption techniques revealed rapid fs-to-ps carrier dynamics followed by slower exciton bleaching on the μs time scale for the oxygen vacancy-rich metal oxides upon photoexcitation, which accounted for the origin of their strong and broad nonlinear optical responses. The strategy provided not only insights into the underlying photophysics of the 2D metal oxides but also fresh ammunition to bring out their remaining potential into full play, such as the fabrication of optoelectronic devices for nonlinear optics. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis converting carbon dioxide into chemical fuels with a high added value is a promising solution to both fossil fuel shortage/pollution and global climate change; however, the development of highly efficient photocatalysts toward this goal is still largely bereft of fresh ideas. Herein, we propose a "cascade electron transfer" strategy through spurring both interfacial and inner electron transfer rates for a 0D/2D photocatalyst of CsPbBr3/CuTCPP metal organic framework (MOF). Upon photoexcitation, the heterojunction structure with an appropriate band alignment facilitates an ultrafast interfacial electron transfer rate of 1.4 ps from CsPbBr3 segment to CuTCPP MOF and subsequent ultrafast internal electron transfer of 21 ps from CuTCPP ligand to the Cu node within the enlarged 2D framework. The efficient electron transfer ensures efficient charge separation favorable for photocatalytic reactions: The photocatalyst exhibits an outstanding yield of 47.2 μmol g−1 h−1 (CO and CH4 combined) superior to previous reports. Rational design of hierarchical heterojunctions with matching electronic bandgap not only expedites cascade charge transfer but also prevents holes from recombining with electrons or oxidizing the photocatalysts without the necessity of sacrificial reagents. This work thus provides useful insight for boosting photocatalytic efficacy from a dynamic perspective. [ABSTRACT FROM AUTHOR]

Direct solvent exfoliation of bulk MoS2 with the assistance of poly(3-hexylthiophene) (P3HT) produces a novel two-dimensional organic/inorganic semiconductor hetero-junction. The obtained P3HT–MoS2 nanohybrid exhibits unexpected optical limiting properties in contrast to the saturated absorption behavior of both P3HT and MoS2, showing potential in future photoelectric applications. [ABSTRACT FROM AUTHOR]

Optical limiters are greatly needed to protect eyes and sensitive optoelectronic devices such as photodetectors and sensors from laser damage, but they are currently plagued by low efficiency. In this work, we utilized Cu 3 VSe 4 nanocrystals (NCs) to enhance laser protection performance, and they exhibit higher saturation intensity and broader nonlinear spectral response extending into the near IR region than the C60 benchmark. A flexible optical limiter goggle prototype based on the NCs significantly attenuated the incident laser beam, with Z scan and I scan measurements demonstrating a giant nonlinear absorption coefficient β value of 1.0 × 10 -7 m W -1 , a large optical damage threshold of 3.5 J cm -2 , and a small starting threshold of 0.22 J cm -2 . Transient absorption spectroscopy disclosed that the origin of the excellent nonlinearity was associated with quasi-static dielectric resonance behavior and a large TPA cross-section of 3.3 × 10 6 GM was measured for Cu 3 VSe 4 NCs, suggesting the potential of intermediate bandgap (IB) semiconductors as alternatives to plasmonic noble metals for ultrafast photonics. Hence, optical limiters based on such semiconductors offer new avenues for laser protection in optoelectronic and defense fields.

New all-inorganic perovskites like Cs 4 PbBr 6 provide rich luminescent tools and particularly novel physical insights, including their zero-dimensional structure and controversial emitting mechanism. The ensuing debate over the origin of the luminescence of Cs 4 PbBr 6 inspired us to tackle the issue through fabricating high-quality Cs 4 PbBr 6 single crystals and employing ultrafast dynamics study. Upon photoexcitation, Cs 4 PbBr 6 underwent dynamics steps distinct from that of CsPbBr 3 , including exciton migration to the defect level on a time scale of several hundred femtoseconds, exciton relaxation within the defect states on the picosecond time scale, and exciton recombination from the subnanosecond to nanosecond time scale. The observation disclosed that crystal defects of Cs 4 PbBr 6 induced green emission while CsPbBr 3 mainly relied on quantum confinement to emit at room temperature. The study provides an in-depth understanding of the photoinduced multistep dynamics steps of Cs 4 PbBr 6 associated with display and photovoltaic applications, establishing Cs 4 PbBr 6 as a new candidate for uses associated with the perovskite family of materials.