Photoluminescence and ODMR studies of lamellar Cd2P2S6 and Zn2P2S6 lattices

ZnPSe3 as ultrabright indirect band-gap system with microsecond excitonic lifetimes

ZnPSe₃ was identified as a two-dimensional material wherein valley and spin can be optically controlled in technologically relevant timescales. We report an optical characterization of ZnPSe₃ crystals that show indirect band-gap characteristics in combination with unusually strong photoluminescence. We found evidence of interband recombination from photoexcited electron-hole states with lifetimes in a microsecond timescale. Through a comparative analysis of photoluminescence and photoluminescence excitation spectra, we reconstructed the electronic band scheme relevant to fundamental processes of light absorption, carrier relaxation, and radiative recombination through interband pathways and annihilation of defect-bound excitons. The investigation of the radiative processes in the presence of a magnetic field revealed spin splitting of electronic states contributing to the ground excitonic states. Consequently, the magnetic field induces an imbalance in the number of excitons with the opposite angular momentum according to the thermal equilibrium as seen in the photoluminescence decay profiles resolved by circular polarization.

Lithium Storage Performance Boosted via Delocalizing Charge in Znx Co1- x PS3 /CoS2 of 2D/3D Heterostructure

A promising anode material consisting of bimetallic thiophosphate Zn_x Co_{1- x} PS₃ and CoS₂ with 2D/3D heterostructure is designed and prepared by an effective chemical transformation. Density functional theory calculations illustrate that the Zn²⁺ can effectively modulate the electrical ordering of Zn_x Co_{1- x} PS₃ on the nanoscale: the reduced charge distribution emerging around the Zn ions can enhance the local built-in electric field, which will accelerate the ions migration rate by Coulomb forces and provide tempting opportunities for manipulating Li⁺ storage behavior. Moreover, the merits of the large planar size enable Zn_x Co_{1- x} PS₃ to provide abundant anchoring sites for metallic CoS₂ nanocubes, generating a 2D/3D heterostructure with a strong electric field. The resultant Zn_x Co_{1- x} PS₃ /CoS₂ can offer the combined advantages of bimetallic alloying and heterostructure in lithium storage applications, leading to outstanding performance as an anode material for lithium-ion batteries. Consequently, a high capacity of 794 mA h g^-1 can be retained after 100 cycles at 0.2 A g^-1 . Even at 3.0 A g^-1 , a satisfactory capacity of 465 mA h g^-1 can be delivered. The appealing alloying-heterostructure and electrochemical performance of this bimetallic thiophosphate demonstrate its great promise for applications in practical rechargeable batteries.

Exfoliated CrPS4 with Promising Photoconductivity

Layered semiconductors have attracted significant attention due to their diverse physical properties controlled by composition and the number of stacked layers. Herein, large crystals of the ternary layered semiconductor chromium thiophosphate (CrPS₄ ) are prepared by a vapor transport synthesis. Optical properties are determined using photoconduction, absorption, photoreflectance, and photoacoustic spectroscopy exposing the semiconducting properties of the material. A simple, one-step protocol for mechanical exfoliation onto a transmission electron microscope grid is developed, and multiple layers are characterized by advanced electron microscopy methods, including atomic resolution elemental mapping confirming the structure by directly showing the positions of the columns of different elements' atoms. CrPS₄ is also liquid exfoliated, and in combination with colloidal graphene, an ink-jet-printed photodetector is created. This all-printed graphene/CrPS₄ /graphene heterostructure detector demonstrates a specific detectivity of 8.3 × 10⁸ (D*). This study shows a potential application of both bulk crystal and individual flakes of CrPS₄ as active components in light detection, when introduced as ink-printable moieties with a large benefit for manufacturing.

Metal Thio- and Selenophosphates as Multifunctional van der Waals Layered Materials

Since the discovery of Dirac physics in graphene, research in 2D materials has exploded with the aim of finding new materials and harnessing their unique and tunable electronic and optical properties. The follow-on work on 2D dielectrics and semiconductors has led to the emergence and development of hexagonal boron nitride, black phosphorus, and transition metal disulfides. However, the spectrum of good insulating materials is still very narrow. Likewise, 2D materials exhibiting correlated phenomena such as superconductivity, magnetism, and ferroelectricity have yet to be developed or discovered. These properties will significantly enrich the spectrum of functional 2D materials, particularly in the case of high phase-transition temperatures. They will also advance a fascinating fundamental frontier of size and proximity effects on correlated ground states. Here, a broad family of layered metal thio(seleno)phosphate materials that are moderate- to wide-bandgap semiconductors with incipient ionic conductivity and a host of ferroic properties are reviewed. It is argued that this material class has the potential to merge the sought-after properties of complex oxides with electronic functions of 2D and quasi-2D electronic materials, as well as to create new avenues for both applied and fundamental materials research in structural and magnetic correlations.

Spectroscopy and Photophysics of Self-Organized Zinc Porphyrin Nanolayers. 3. Fluorescence Detected Magnetic Resonance of Triplet States

Fluorescence detected magnetic resonance (FDMR) has been applied to approximately 25-nm-thick porphyrin films, containing ordered domains of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides. Illuminating the films at 1.4 K with 457.9-nm light from a continuous wave Ar(+) laser produces at least two different, Jahn-Teller-distorted, ZnTOPP triplet species, labeled i and ii. Microwave-induced magnetic resonance of i and ii in the absence or presence of an externally applied magnetic field affects the fluorescence intensity of ZnTOPP, thus allowing FDMR. For triplet species i, formed in films spin-coated from toluene solution, the zero-field splitting (ZFS) parameters were determined as |D| = (316.9 +/- 0.1) x 10(-4) cm(-1) and |E| = (32.0 +/- 0.5) x 10(-4) cm(-1). By exposure of the spin-coated films to chloroform vapor at room temperature, triplet i is converted into species ii, with |D| = (295 +/- 3) x 10(-4) cm(-1) and |E| = (121 +/- 3) x 10(-4) cm(-1). For the excited triplet state of ZnTOPP in a toluene glass, ZFS parameters with values of |D| = (295 +/- 1) x 10(-4) cm(-1) and |E| = (91 +/- 1) x 10(-4) cm(-1) are found. From a combined study of the FDMR- and microwave-induced fluorescence spectra, i and ii are identified as unligated and ligated ZnTOPP triplet species, respectively. From the asymmetrically shaped zero-field FDMR signals of i, we conclude that the local crystal field perturbations of the stacked molecules are anisotropic. The FDMR results of the ZnTOPP films are compared with those for a film of zinc tetraphenylporphyrin (ZnTPP), which lacks the octyl substituents, and therefore is nonordered. Upon illumination, the ZnTPP films contain only a single, ligated, triplet species with ZFS parameters very similar to those of ligated ZnTOPP. At approximately 5 K, the lifetime of triplet i is considerably shortened compared to that of ZnTOPP in a glass at the same temperature.