Zhongpo Zhou

Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) quasi‐2D perovskites exhibit disparate chemical bonds and structures due to distinct organic spacer cations, endowing them with distinctive physical properties. A more far‐reaching investigation of the fundamental structure–physical relation, including the carrier dynamics, is expected in these layered perovskites. The phase distribution, defect state density, and ultrafast dynamics of RP‐type perovskite (PA) ₂ () ₃ and DJ‐type perovskite (HDAD) () ₃ were investigated by using transient absorption spectra. The DJ‐type perovskite exhibits a lower threshold amplified spontaneous emission (ASE); however, its Auger recombination is more severe than that of RP‐type perovskite. By adding a trace amount of HBr to the solvent during crystal growth, exciton–phonon coupling was inhibited, energy transfer was promoted, and the Auger recombination was suppressed. We ultimately chose the HBr‐treated HDAD quasi‐2D perovskite thin films, achieving a low ASE threshold and high‐performance single‐mode green lasers.

Understanding how quantum confinement governs spin-resolved dynamics is essential for the development of perovskite-based spin photonics. Here, we systematically investigate exciton spin relaxation in thickness-tunable CsPbBr3 nanoplatelets via circularly polarized transient absorption spectroscopy. At early delay times (∼0.4 ps), state-filling and Pauli exclusion lead to photoinduced absorption signals on opposite energetic sides of the exciton bleach under different circular polarizations. The same polarization spectra exhibit a thickness-dependent sign reversal on the low-energy side of the exciton bleach, arising from the shifting balance between band gap renormalization and rapid radiative recombination. Furthermore, the spin lifetime increases from 0.27 ps for 2-monolayer nanoplatelets to 1.22 ps for 6-monolayer nanoplatelets due to reduced spatial wave function overlap and suppressed exchange interactions. This work provides a crucial framework for designing perovskite gain media and spin-optoelectronic devices.

Triplet sensitization of semiconductor nanocrystals is important in photocatalysis and photodynamic therapy. However, current photosensitizers often contain toxic or precious metals, making the development of environmentally benign nanocrystal-based systems challenging due to scarce suitable materials and insufficient understanding of excited-state transfer. Herein, we investigate triplet energy transfer from CuInS ₂ /ZnS nanorods to surface-anchored 9-anthracene carboxylic acid acceptors, with a rate constant of 1.02 × 10 ¹⁰ s ⁻¹ and 90% efficiency. Besides, the transferred spin-triplet states undergo triplet–triplet annihilation in the interfaced annihilator molecules of diphenyl anthracene, enabling photon upconversion with a threshold of 23.26 W/cm² and an efficiency of 6.8%. These findings highlight CuInS ₂ /ZnS nanorods as nontoxic triplet sensitizers and provide a viable strategy for sustainable upconversion optoelectronic devices.

Quasi-two-dimensional (quasi-2D) Dion–Jacobson (DJ) perovskites modified with large organic cations exhibit superior optoelectronic properties and stability compared to their three-dimensional (3D) counterparts, making them promising for light-emitting diodes and lasing applications. While diammonium cations with linear chain structures are preferred due to their hydrogen-bonding capability and enhanced structural stability, the effect of cation chain length remains insufficiently understood. Here, we systematically investigate three diammonium spacers with varying chain lengths. Ultrafast spectroscopy reveals that longer-chain cations promote pronounced phase separation, which facilitates the formation of a high-quality n=2 phase, uniform phase distribution, efficient energy transfer, and suppressed non-radiative recombination. These effects collectively reduce the amplified spontaneous emission threshold, from 41.94 μJ/cm2 (EDA, short-chain) and 29.86 μJ/cm2 (BDA, medium-chain) to an ultralow 7.67 μJ/cm2 (PentDA, long-chain). Using this optimized gain medium, we demonstrate a single-mode vertical-cavity laser with a threshold of 6.75 μJ/cm2, a narrow linewidth of 0.49 nm, and a high-quality factor of 1093.8. Conversely, short-chain cations lead to weak phase separation and an insufficient n=2 phase content, resulting in film transient absorption characteristics dominated by excited-state absorption. This study clarifies the critical role of cation chain length in tuning the phase behavior and optical gain of quasi-2D DJ perovskites, providing guidance for their use in low-threshold laser devices.

Quasi-two-dimensional (2D) Dion–Jacobson (DJ) perovskites demonstrate remarkable photophysical properties and exhibit tremendous potential in amplified spontaneous emission (ASE) and lasing. However, their inferior crystallinity and the inappropriate multiphase structure in the quasi-2D perovskite seriously affect the energy transport efficiency in the energy funnel and the lasing threshold, which severely impedes the pace of development in this emerging area. Here, we report a green ASE with a low threshold of 8.2 μJ/cm2, accomplished by introducing an ionic liquid additive strategy that refines the crystallization kinetics, passivates defect-rich small-n (n = 1, 2) phases, and improves energy funneling in the quasi-2D (BDA)(MA)3Pb4Br13 perovskite film. The single-mode vertical-cavity laser is demonstrated with a low threshold of 9.98 μJ/cm2, a narrow linewidth of 0.47 nm, and a quality factor of 1125.3. This work will be helpful for further prompting the performances of the low-threshold lasers based on DJ perovskites.

The generation of terahertz (THz) radiation by a photoconductive antenna (PCA) is investigated through the interaction between a laser and a semiconductor. The dynamic changes of charge carriers on the antenna surface under 50 fs laser excitation ( λ = 800 nm) are simulated using COMSOL Multiphysics v6.1 software based on the finite element method. The electric field radiation resulting from changes in the semiconductor surface electric current is simulated using CST Studio Suite 2022. A new PCA with unequal spacing electrodes is presented, which generates a non-uniform field using a metal microstructure (500 nm height, 500 nm diameter). Finite-difference time-domain (FDTD) simulations revealed more pronounced surface plasmon resonance enhancement effects for the new PCA, with a ~1.3 times increase in light absorptivity and a ~130 times increase in electric field intensity. This leads to a ~1.6 times enhancement in THz radiation intensity. Additionally, the directivity of the new PCA increases from 1.2 dBi to 7.17 dBi at 1.3 THz. This PCA is designed for straightforward fabrication and significantly enhances THz radiation intensity, aiming to meet the demands of rapidly developing communication technologies.

Quasi-two-dimensional (quasi-2D) Dion-Jacobson (DJ)-type perovskites have recently received growing attention in photoelectronics for their excellent photophysical properties. However, the uncontrollable nature of the crystallization process increases the density of defect states, constraining further improvement in device efficiency. In this study, we investigated the phase distribution, energy transfer, and Auger recombination in quasi-2D perovskite HDAD(FA0.8Cs0.2)4Pb5Br16 thin films through additive methods. The results demonstrate that the incorporation of EABr enhances the radiative recombination efficiency of DJ-type perovskites. More importantly, we realized green amplified spontaneous emission and single-mode vertical-cavity surface-emitting lasing with low thresholds of 8.5 and 12.67 μJ/cm2, respectively. This study presents an approach for fabricating high-performance green lasers.