Induced ferromagnetism in Ni(II) doped ZnO monolayers via Al co-doping and their optical characteristics:ab initiostudy.

For applications in magneto-electronic devices, diluted magnetic semiconductors (DMSs) usually exhibit spin-dependent coupling and induced ferromagnetism at high Curie temperatures. The processes behind the behavior of optical emission and ferromagnetism, which can be identified by complicated microstructural and chemical characteristics, are still not well understood. In this study, the impact of Al co-doping on the electronic, optical, and magnetic properties of Ni(II) doped ZnO monolayers has been investigated using first principles calculations. Ferromagnetism in the co-doped monolayer is mainly triggered by the exchange coupling between the electrons provided by Al co-doping and Ni(II)-dstates; therefore, the estimated Curie temperature is greater than room temperature. The spin-spin couplings in mono-doped and co-doped monolayers were explained using the band-coupling mechanism. Based on the optical study, we observed that the Ni-related absorption peak occurred at 2.13-2.17 eV, showing a redshift as Ni concentrations increased. The FM coupling between Ni ions in the co-doped monolayer may be responsible for the reduction in the fundamental band gap seen with Al co-doping. We observed peaks in the near IR and visible regions of the co-doped monolayer, which improve the optoelectronic device's photovoltaic performance. Additionally, the correlation between optical characteristics and spin-spin couplings has been studied. We found that the Ni(II)'sd-dtransition bands or fundamental band gap in the near configuration undergoes a significant shift in response to AFM and FM coupling, whereas in the far configuration, they have a negligible shift due to the paramagnetic behavior of the Ni ions. These findings suggest that the magnetic coupling in DMS may be utilized for controlling the optical characteristics.

Photon-carrier-spin coupling in a one-dimensional Ni(II)-doped ZnTe nanostructure.

Transition metal (TM) ion doping in II-VI semiconductors can produce exciton magnetic polarons (EMPs) and localized EMPs containing longitudinal optical (LO) phonon coupling, which will be discussed in this paper. TM ion doping in II-VI semiconductors for a dilute magnetic semiconductor show emission via magnetic polarons (MPs) together with hot carrier effects that need to be understood via its optical properties. The high excitation power that is responsible for hot carrier effects suppresses the charge trapping effect in low exciton binding energy (8.12 meV) semiconductors, even at room temperature (RT). The large polaron radius exhibits strong interaction between the carrier and MP, resulting in anharmonicity effects, in which the side-band energy overtone to LO phonons. The photon-like polaritons exhibit polarized spin interactions with LO phonons that show strong spin-phonon polaritons at RT. The temperature-dependent photoluminescence spectra of Ni-doped ZnTe show free excitons (FX) and FXs interacting with 2LO phonon-spin interactions, corresponding to3T1(3F) →1T1(1G) and EMP peaks with ferromagnetically coupled Ni ions at3T1(3F) →1E(1G). In addition, other d-d transitions of single Ni ions (600-900 nm) appear at the low-energy side. RT energy shifts of 14-38 meV are observed due to localized states with density-of-states tails extending far into the bandgap-related spin-induced localization at the valence band. These results show spin-spin magnetic coupling and spin-phonon interactions at RT that open up a more realistic new horizon of optically controlled dilute magnetic semiconductor applications.

Bound magnetic polaron in Zn-rich cobalt-doped ZnSe nanowires.

The micro-luminescence spectra of the diluted magnetic semiconductor (DMS) can reflect the spin-exciton interaction and related relaxation process. Here the micro-photoluminescence (micro-PL) spectra and PL lifetime measurements have been done on an individual ferromagnetic (FM)-coupled cobalt (Co) doped zinc selenide (ZnSe) nanowire. There occurs a double-peak profile in its near bandedge emission spectrum: the first peak is from free exciton (FX) and the second comes from magnetic polaron (MP). In their temperature dependent PL spectra, the MP emission peak demonstrates obviously temperature-independent behavior, in contrast to the behaviors of FX and reported exciton MP in nanobelt. It is found that in this Co(II) doped ZnSe nanowires, this MP's temperature-independent emission is related to the coupling between exciton and a FM nanocluster (↑↑↓). The nanocluster is likely due to the interaction of Se vacancies of the wide bandgap semiconductors with the antiferromagnetic (AFM) arrangement transition metal (TM) ions in these Se-deficient Co doped ZnSe nanowires. These results reflect that the AFM coupling TM ions pair can give rise to FM behavior with the involvement of positive charge defect, also indicating that the micro-luminescence detection can be used to study the magnetic coupling in DMS.

The Preparation and Optical Properties of Ni(II) and Mn(II) Doped in ZnTe Nanobelt/Nanorod by Using Chemical Vapor Deposition.

The doping techniques are often used to modify the properties of semiconductors. Transition metal ion doping in semiconductor can lead to dilute magnetic semiconductors (DMSs), which may initiate some novel properties related to spins. In contrast to the wide band semiconductor ZnO, ZnSe and CdS crystal the transition metal (TM) ion aggregate can be the origin of the ferromagnetic behaviors, which influence their optical properties mainly through the exciton-spin interactions due to their high exciton binding energy. For narrow band semiconductor, the carrier-spin coupling is the main cause of magnetism as observed in ZnTe. The ZnTe nanobelt for DMS with the TM ions such as Ni(II) and Mn(II) doping mainly induce the excess carrier effect in the lattice after photo-excitation, whose optical properties are also strongly depended on the fabrication method structure and morphology. Photo-excited carriers and electron-phonon interaction (but less excitons) are responsible for their large redshifts in ZnTe nanostructures. The strong interaction between the doped magnetic ion spins and holes, electron-phonon coupling, p-d hybridization as well as local electron correlation in TM ions determined their optical properties. TM ions incorporation in ZnTe lattice has suppressed the broad defect emission band far from the bandedge and broadened the electron correlations and electron hole plasma band near bandedge when excited by the rising excitation powers. We also identified that the polarized PL of Ni(II) and Mn(II) doped samples to calculate the strain dependence of band splitting near valance band.

Optically programmable encoder based on light propagation in two-dimensional regular nanoplates.

We design an efficient optically controlled microdevice based on CdSe nanoplates. Two-dimensional CdSe nanoplates exhibit lighting patterns around the edges and can be realized as a new type of optically controlled programmable encoder. The light source is used to excite the nanoplates and control the logical position under vertical pumping mode by the objective lens. At each excitation point in the nanoplates, the preferred light-propagation routes are along the normal direction and perpendicular to the edges, which then emit out from the edges to form a localized lighting section. The intensity distribution around the edges of different nanoplates demonstrates that the lighting part with a small scale is much stronger, defined as '1', than the dark section, defined as '0', along the edge. These '0' and '1' are the basic logic elements needed to compose logically functional devices. The observed propagation rules are consistent with theoretical simulations, meaning that the guided-light route in two-dimensional semiconductor nanoplates is regular and predictable. The same situation was also observed in regular CdS nanoplates. Basic theoretical analysis and experiments prove that the guided light and exit position follow rules mainly originating from the shape rather than material itself.

Synthesis of Novel Sea-Urchin-Like CdS and Their Optical Properties.

A novel morphology of CdS sea-urchin-like microstructures is synthesized by simple thermal evaporation process. Microstructures with average size of 20-50 µm are composed of single crystalline CdS nanobelts. The structural, compositional, morphological characterization of the product were examined by X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectroscopy, scanning electron microscope, transmission electron microscopy and selected area electron diffraction while optical properties are investigated by Photoluminescence spectroscopy and time-resolved Photoluminescence measurements. The tentative growth mechanism for the growth of sea-urchin-like CdS is proposed and described briefly. A strong green emission with a maximum around 517 nm was observed from the individual CdS microstructure at room temperature, which was attributed to band-edge emission of CdS. These Novel structures exhibit excellent lasing (stimulated emission) with low threshold (9.07 µJ cm(-2)) at room temperature. We analyze the physical mechanism of stimulated emission. These results are important in the design of green luminescence, low-threshold laser and display devices in the future.

Synergetic enhancement of CsPbI3 nanorod-based high-performance photodetectors via PbSe quantum dot interface engineering.

The advancement of optoelectronic applications relies heavily on the development of high-performance photodetectors that are self-driven and capable of detecting a wide range of wavelengths. CsPbI3 nanorods (NRs), known for their outstanding optical and electrical properties, offer direct bandgap characteristics, high absorption coefficients, and long carrier diffusion lengths. However, challenges such as stability and limited photoluminescence quantum yield have impeded their widespread application. By integrating PbSe colloidal quantum dots (CQDs) with CsPbI3 NRs, the hybrid nanomaterial harnesses the benefits of each component, resulting in enhanced optoelectronic properties and device performance. In this work, a self-powered and broadband photodetector, ITO/ZnO/CsPbI3:PbSe/CuSCN/Au, is fabricated, in which CsPbI3 NRs are decorated with PbSe QDs as the photoactive layer, ZnO as the electron-transporting layer and CuSCN as the hole-transporting layer. The device performance is further improved through the incorporation of Cs2CO3 into the ZnO layer, resulting in an enhancement of its overall operational characteristics. As a result, a notable responsivity of 9.29 A W-1 and a specific detectivity of 3.17 × 1014 Jones were achieved. Certainly, the TCAD simulations closely correlate with our experimental data, facilitating a comprehensive exploration of the fundamental physical mechanisms responsible for the improved performance of these surface-passivated heterojunction photodetectors. This opens up exciting possibilities for substantial advancements in the realm of next-generation optoelectronic devices.

Two Bulk-Heterojunctions Made of Blended Hybrid Nanocomposites for High-Performance Broadband, Self-Driven Photodetectors.

Heterojunctions based on low dimensional semiconducting materials are one of the most promising alternatives for next-generation optoelectronic devices. By choosing different dopants in high-quality semiconducting nanomaterials, p-n junctions can be realized with tailored energy band alignments. Also, p-n bulk-heterojunctions (BHJs) based photodetectors have shown high detectivity because of the suppressed dark current and high photocurrent, which are due to the larger built-in electric potential within the depletion region and can significantly improve the quantum efficiency by reducing the carriers' recombination. In this work, PbSe quantum dots (QDs) blended with ZnO nanocrystals (NCs) were used as the n-type layer, while CsPbBr3 NCs doped with P3HT were used as the p-type layer; as a result, a p-n BHJ was formed with a strong built-in electric field. Consequently, such a kind of p-n BHJ photodetector ITO/ZnO/PbSe:ZnO/CsPbBr3:P3HT/P3HT/Au showed a high ON/OFF current ratio of 105 with a photoresponsivity of 1.4 A/W and specific detectivity of 6.59 × 1014 Jones under 0.1 mW/cm2 532 nm illumination in self-driven mode. Moreover, the simulation performed by TCAD also agrees well with our experimental results, and the underlying physical mechanism for enhanced performance is discussed in detail for this type of p-n BHJ photodetector.