Yuzong Gu

Despite progress in sodium‐ion batteries, developing cathodes with high stability and performance under harsh conditions remains a critical challenge. Herein, a sustainable in‐situ Zn substitution method to partially replace Fe in sodium iron hexacyanoferrate (FeHCF) using ZnO as the precursor under acidic media. The resulting Zn‐FeHCF‐2 exhibits a lower amount of coordinated water (∼10.75%), effectively alleviating lattice strain during repeated Na ⁺ insertion/extraction. As a result, the material delivers highly reversible electrochemical behavior with minimal volume variation according to in‐situ XRD. Structural analyses reveal uniform cubic particles with high crystallinity, contributing to mechanical stability and improved charge‐transfer kinetics. Electrochemically, the cathode achieves a specific capacity of ∼158.98 mAh g ⁻¹ at 0.1 C and maintains excellent rate capability up to 50 C. Moreover, a full cell assembled with Zn‐FeHCF‐2||hard carbon anode retains 96.5% of its initial capacity (88.34mAh g ⁻¹ ) after 6000 cycles at −20°C. Additionally, density functional theory (DFT) calculations indicate that zinc incorporation lowers the energy barriers for sodium‐ion diffusion, thereby facilitating faster reaction kinetics.

The heterojunction engineering can provide an effective platform for optimizing and synthesizing the properties of nanomaterials. Herein, the TiS ₂ powder was synthesized via the solid-phase sintering method and the TiS ₂ /graphene (TiS ₂ /G) heterostructure film with enhanced saturable absorption was developed by using the liquid-phase exfoliation and the layer-by-layer spin-coating techniques. Measurement results at 2.8[ ][ ]m revealed that it exhibited a modulation depth of [ ]5.7%, an obvious enhancement compared to the [ ]4.2% of pure TiS ₂ film, meanwhile, the saturation intensity was [ ]0.12[ ]MW/cm ² , markedly lower than [ ]0.17[ ]MW/cm ² of solo TiS ₂ device. With this SAM, a robust passively Q-switched Er:YAP bulk laser operating at [ ]2.8[ ][ ]m was demonstrated. The maximal signal-to-noise ratio of the stable pulse sequence reached 35[ ]dB at an absorbed pump power of 6.1[ ]W, with a repetition rate of 177.3[ ]kHz, a pulse width of 232[ ]ns and an average output power of 0.42[ ]W. This functional TiS ₂ /Graphene heterostructure film can provide an available optical modulator for a robust passively Q-switched laser operation in the mid-infrared band.

Mid-infrared (Mid-IR) pulsed lasers are vital for diverse applications, yet their development is hindered by the scarcity of high-performance saturable absorbers (SAs) for Q-switching and mode-locking. While graphene and its analogs have emerged as promising candidates, their low modulation depth in the mid-IR regime hinders its practical implementation. To overcome this, we engineer a Ti:Sb₂Te₃/reduced graphene oxide (rGO) heterostructure via hydrothermal synthesis, leveraging synergistic Ti⁴⁺ doping and interfacial charge control. Ti⁴⁺ introduces tailored trap states in Sb₂Te₃ nanosheets—selected for their narrow bandgap and high mobility—suppressing non-radiative recombination and extending carrier lifetimes. This defect-mediated design achieves a significantly enhanced modulation depth of 1.8% (2.4× higher than graphene) and a nonlinear absorption coefficient of 6.84 cm GW⁻¹ at 2.8 μm. Transient absorption spectroscopy confirms trap-assisted carrier dynamics and accelerated charge transfer. Integrating the heterostructure as an SA mirror into an Er:YAP laser generates stable 2.8 μm pulses with a 253 ns width, 163 kHz repetition rate, and 230 mW peak power at 5.5 W pump power. This work demonstrates defect-engineered Ti:Sb₂Te₃/rGO as a promising high-performance mid-IR SA for narrow-pulse lasers.

The systematic and comprehensive research on the single-pass second harmonic generation (SHG) of the perfect vortex beam (PVB) under low fundamental wave depletion is reported. Based on Fourier transformation of the Bessel-Gaussian vortex beam (BGVB) generated through the combination of the spiral phase plate and the axicon, the perfect vortex beam (PVB) at 1064 nm with topological charge (TC) up to 6 is created. By single-pass SHG of these PVBs through the MgO-doped, periodically poled congruent LiNbO₃ crystal, PVBs at green wavelength (532 nm) with TCs up to 12 are generated. The TC of the PVB is identified by the interferogram between the PVB and the reference TEM₀₀ Gaussian beam. The SH power (efficiency) of the PVB is measured to be independent of the TC. Furthermore, the impacts of beam parameters, including the ring radius (ρ) and the ring half-width (Δ), on the SH efficiency of the PVB, are also investigated. The SH efficiency is inversely proportional to both the ring radius ρ and ring half-width Δ. Experimental results agree well with those theoretical ones. The SH PVB transforms to the BGVB at the far-field. The paper also indicates that by transforming the Laguerre–Gaussian vortex beam (LGVB) into the PVB, the detrimental impact that the SH efficiency of LGVB decreases with the increase of TC value can be effectively mitigated, and high SH efficiency can be maintained even at high TC value.

In this work, we demonstrate a Watt-level, high-quality Laguerre–Gaussian (LG) LG_0±1 vortex mode directly output from an end-pumped Nd:YVO₄ laser by using an axicon-based annular pump beam. A theoretical model for the annular beam end-pumped solid-state laser with an LG vortex mode output was established. Chirality control of the vortex laser was achieved by carefully tilting the output coupler. Watt-level 1064 nm lasers with pure LG_0,1/LG_0,−1 vortex mode, and the incoherent superposition mode of LG_0,1 odd and even petal modes, were achieved successively in our experiments. The intensity profile of the generated pure LG_0,1 vortex laser was measured, and it can be well fitted by using the standard expression of the LG_0,1 vortex mode. The beam quality of the pure LG_0,1 mode is M_x² = 2.01 and M_y² = 2.00 along the x-axis and y-axis, respectively. Our study demonstrates that that axicon-based annular pumping has great potential in developing high-power vortex solid-state lasers with simple and compact structures.

The composite of graphene and semiconductor nanoparticles has attracted increasing interest in the search for novel nonlinear optical materials. Herein, composites of reduced graphene oxide (RGO) and SnO₂ nanoparticles with different mass ratios were synthesized via a facile hydrothermal method. The structural morphology and basic physical properties of the SnO₂/RGO composites were characterized using TEM, SEM, XRD, Raman, XPS and UV–Vis spectra, indicating that SnO₂ nanoparticles were uniformly anchored on the surface of graphene nanosheets through covalent and partial-ionic bonds. The third-order optical nonlinearities of the composites were studied for the first time by the Z-scan technique using a picosecond laser at 532 nm. It was found that the composites demonstrated saturable absorption and positive nonlinear refraction properties, and both were significantly enhanced compared with pure SnO₂ nanoparticles and RGO nanosheets, and the enhancement was tunable with the variation of SnO₂:GO mass ratio. The maximum saturable absorption coefficient and the third-order susceptibility of the as-prepared SnO₂/RGO composites were obtained to be −2.93×10^–11 m W⁻¹ and 2.25 × 10^–11 esu, respectively. The maximum saturable absorption modulation depth obtained was 10% with the corresponding saturation light intensity of 0.3 GW cm⁻². Moreover, the optimised third-order susceptibility of SnO₂/RGO was found much greater than many other materials ever studied. Several involved factors contributing to the nonlinearities were discussed. The results propose that the third-order optical nonlinearities of SnO₂/RGO and other similarly structured composites can be potentially tuned to meet certain application requirements of nonlinear optical devices by controlling the mass ratio of semiconductor to graphene.

Ni‐rich layered oxides have been intensively considered as promising cathode materials for next‐generation Li‐ion batteries. Nevertheless, the performance degradation caused by intergranular cracks and electrode/electrolyte interface parasitic reactions restricts their further application. Compared with secondary particles, single‐crystal (SC) materials have better mechanical integrity and cycling stability. However, the preparation of ultrahigh‐nickel layered SC cathode still remains a serious challenge. Herein, a novel LiOH‐LiNO₃‐H₃BO₃ molten‐salt method is proposed to synthesize SC LiNi_0.92Co_0.06Mn_0.02O₂ with considerable crystallinity and uniformity. The critical impacts of calcination temperature and boric acid on the microstructure and electrochemical property of Ni‐rich layered oxides are systematically investigated. The results show that the crystal growth is promoted and the stability of crystal structure is improved by this synthesis method. In particular, the optimal electrode demonstrates a superior initial discharge capacity of 214.8 mAh g^–1 with a high capacity retention of 86.3% over 300 cycles as tested by pouch‐type full cells at 45 ºC. This work not only prepares an ultrahigh‐nickel layered CS cathode with superior electrochemical performances, but also provides a feasible method for the synthesis of other CS layered cathode materials.

Graphene has broad prospects for application in photonic devices. However, its zero-band gap limits its nonlinear optical (NLO) properties, and thus, its application. In this study, we synthesized reduced graphene oxide modified by Mn-doped semiconductor CdS nanoparticles (RGO/CdS:Mn) via a solvothermal method to study the development of NLO properties of graphene. The structures, morphologies and basic physical properties of RGO, CdS, RGO/CdS, and RGO/CdS:Mn were characterized. The third-order optical nonlinearities were tested by the Z-scan technique using a mode-locked Nd:YAG laser operating at 532 nm with a 30 ps pulse width. The results showed that the nonlinear susceptibility and saturation absorption of RGO/CdS:Mn were 15.3 and 26 times higher than those of RGO, respectively. The mechanism of the enhancement was analyzed based on the charge transfer between and within the components, and Mn doping produced trapping effect. The significantly improved optical nonlinearity of RGO/CdS:Mn lays a foundation for its applications in photonic devices.