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2D orthorhombic palladium diselenide is attracting rapidly increased interest by virtue of its fascinating physical properties and feasibility of phase transformation. However, it remains a major challenge to produce ultrathin PdSe2 through a facile chemical route and control phase transformation because of its anisotropic structure with strong interlayer coupling. Here, the efficient synthesis of few‐layer PdSe2 nanosheets with large sizes using an electrochemical exfoliation approach is reported. Upon thermal annealing at 300–350 °C, the as‐exfoliated PdSe2 nanosheets transform into metallic phase PdSe2‐x, as verified by scanning transmission electron microscopy, Raman spectroscopy, and electrical characterizations. Simple encapsulation using hexagonal boron nitride (h‐BN) can effectively suppress the Se‐loss triggered phase transformation, so that a metal‐semiconductor junction is formed by local phase modification. The fabricated PdSe2 field‐effect transistors exhibit p‐type transport property, which is in stark contrast to electron‐dominated ambipolar transport of pristine PdSe2 devices. The combination of high‐resolution X‐ray photoelectron spectroscopy and cross‐sectional transmission electron microscopy analysis reveals that the modulation of carrier polarity in h‐BN encapsulated PdSe2 should arise from the p‐doping effect associated with the impact of interfacial condition. The study opens up a new route for future phase‐engineered electronics in PdSe2 and other 2D noble metal dichalcogenides materials. [ABSTRACT FROM AUTHOR]

Phonon-assisted upconversion process is one of the important means to generate upconversion photoluminescence (UCPL), and has important applications in laser refrigeration and other fields. However, until now, the studies on UCPL behavior are still insufficient. Herein, this work synthesizes a series of Mn-doped two-dimensional hybrid metal halide (2D HMH) thin films and investigates their optical properties using various spectral techniques. Raman spectroscopic measurement confirms that Mn-doping is achieved via interstitial doping rather than Pb-substitution. By the measurement of the temperature-dependent PL spectrum, it is found that Mn-doping will weaken the thermal expansion effect of 2D HMHs, but will enhance the electron–phonon coupling strength. More importantly, both two-photon-excited and phonon-assisted UCPL are observed in Mn-doped 2D HMHs, with an extremely large phonon-assisted energy gain (approximately 500 meV). Our experimental results are of significance for designing phonon-assisted UCPL materials and expanding their applications. [ABSTRACT FROM AUTHOR]

Core–shell perovskite nanocrystals (NCs) have emerged as a promising class of materials for optoelectronic applications due to their unique properties and stability. Although much research has been conducted on the shell growth mechanism and properties of the core–shell NCs, little is known about the role of shell thickness in determining their optical properties. Herein, a heteroepitaxial method is employed to prepare a series of core–shell FAPbBr3/CsPbBr3 NCs with different shell thicknesses. Through temperature‐dependent photoluminescence measurement, it is found that the electronic structure of core–shell FAPbBr3/CsPbBr3 NCs evolves from quasi‐type‐II to type‐I with the increase in shell thickness. This abnormal transition can be attributed to the thickened gradient alloy layer FA1‐xCsxPbBr3, which effectively relieves the lattice mismatch and releases strain in the NCs, resulting in variations in the bandgap between the core and the shell. Furthermore, the biexciton Auger lifetimes in these samples exhibit a non‐monotonic dependence on shell thickness, indicating the electronic structure transition. These results provide valuable insights into the relationship between shell thickness, electronic structure, and optical properties in core–shell perovskite NCs, which may offer guidance for the design of high‐performance optoelectronic devices. [ABSTRACT FROM AUTHOR]

Lead halide perovskite nanocrystals (PeNCs) have attracted intense interest by virtue of their numerous remarkable optoelectronic properties, which render them promising for various optoelectronic applications. Over the past few years, substantial progress has been made in the study of chiral PeNCs, from the sample preparation, spectroscopic characterization to practical applications. In this review, the state‐of‐the‐art progress of the construction strategies and photophysical properties of chiral PeNCs has been summarized. The focus is placed on emerging developments in terms of synthetic methods, chiroptical properties, nonlinear optics, and chiral spintronics in chiral PeNCs. In the end, there is a discussion on the current challenges and future prospects in this versatile, rapidly evolving field. [ABSTRACT FROM AUTHOR]

Photo-generated dynamics have been extensively studied in two-dimensional (2D) heterostructures, such as MoSe2/WSe2 and MoSe2/MoS2. Here, we fabricate few-layer PbI2 and monolayer MoSe2 van der Waals (vdW) heterostructures. The excited-wavelength dependent measurements of photoluminescence (PL) and transient dynamic absorption spectra show that there is almost no photo-generated charge transfer between PbI2 and MoSe2. PL changes of MoSe2 are rather dominated by the Fermi level (EF) modulation through the interlayer charge transfer. Density functional theory calculation shows that binding energies in the heterostructures of MoSe2/WSe2 or MoSe2/MoS2 are 2–3 times higher than that of the MoSe2/PbI2 heterostructure, suggesting the weaker interlayer coupling between MoSe2 and PbI2. We propose that the weak interlayer vdW coupling cannot drive the photo-generated interlayer charge transfer while the EF modulation can be achieved through the interlayer charge transfer. The findings will be helpful to fundamental research and applications for novel optoelectronic devices based on 2D material vdW heterostructures. [ABSTRACT FROM AUTHOR]