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Electrochemical nitrogen reduction reaction (NRR) is a promising approach for NH3 production to take place of the traditional Haber-Bosch process, which is still limited by the low NH3 yield rate and low Faradaic efficiency. Herein, Ti was post-synthetic exchanged into Zr-based metal organic frameworks to synthesize UiO-Zr-Ti as NRR electrocatalysts. The incorporated Ti is found to function as active sites for NRR and benefit the improved charge-transfer efficiency, which has a positive effect on the high NH3 yield rate. Moreover, the existence of Zr and Ti species can effectively suppress the competing HER, thus leading to high Faradaic efficiency. Therefore, the modified UiO-Zr-Ti-5d shows the highest NH3 yield rate of 1.16 × 10−10 mol cm−2 s−1 and the highest Faradaic efficiency of 80.36%, which is comparable to recently reported NRR electrocatalysts.

To meet the demand of producing hydrogen at low cost, a molybdenum (Mo)-doped cobalt oxide (Co3O4) supported on nitrogen (N)-doped carbon (x%Mo–Co3O4/NC, where x% represents Mo/Co molar ratio) is developed as an efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This defect engineering strategy is realized by a facile urea oxidation method in nitrogen atmosphere. Through X-ray diffraction (XRD) refinement and other detailed characterizations, molybdenum ion (Mo4+) is found to be doped into Co3O4 by substituting cobalt ion (Co2+) at tetrahedron site, while N is doped into carbon matrix simultaneously. 4%Mo–Co3O4/NC is the optimized sample to show the lowest overpotentials of 91 and 276 mV to deliver 10 mA cm−2 for HER and OER in 1 M potassium hydroxide solution (KOH), respectively. The overall water splitting cell 4%Mo–Co3O4/NC||4%Mo–Co3O4/NC displays a voltage of 1.62 V to deliver 10 mA cm−2 in 1 M KOH. The Mo4+ dopant modulates the electronic structure of active cobalt ion (Co3+) and boosts the water dissociation process during HER, while the increased amount of lattice oxygen and formation of pyridinic nitrogen due to Mo doping benefits the OER activity. Besides, the smaller grain size owing to Mo doping leads to higher electrochemically active surface area (ECSA) on 4%Mo–Co3O4/NC, resulting in its superior bifunctional catalytic activity.

In this letter, a novel acousto-optical (AO) Q-switch is designed by using $\alpha $ -BaTeMo $_{\mathbf {2}}~\text{O}_{\mathbf {9}}$ crystal grown by the flux method. The acousto-optical modulator (AOM) exhibits a high polarization extinction ratio of 65 dB with a rise time of 32.8 ns and insertion loss of 3.66 dB. An actively Q-switched ytterbium doped all fiber laser at 1035 nm is successfully realized by using the prepared AOM. Under a pump power of 404.9 mW, a maximum output power of 1.66 W is obtained with pulse width of 167 ns at the modulation rate of 10 kHz. The results show that the $\alpha $ -BaTeMo $_{\mathbf {2}}~\text{O}_{\mathbf {9}}$ AOM is a potential Q-switch for all fiber lasers.

Co-Nd2O3/N-doped carbon (NC) as bifunctional oxygen electrocatalyst was synthesized by annealing a bimetal precursor (Co, Nd). It exhibits a nanostructure of Co-Nd2O3 hybrid nanoparticles coated with NC shells. The introduced Nd2O3 is beneficial to obtain high ratios of O vacancy/total O and graphitic-N/total N and modify the Lewis acidic property of Co-Nd2O3/NC-700, thus benefiting the OER activity. Besides, not only high Co2+/total Co and pyridinic-N/total N ratios, but also the enhanced Lewis base property is achieved after the introduction of Nd2O3, which is favorable for the ORR activity. As a result, the optimal Co-Nd2O3/NC-700 exhibits the enhanced OER/ORR activity. Especially, the OER activity is remarkably improved, thus leading to the excellent bifunctional catalytic activity with low ΔE of ∼0.86 V. Furthermore, the Zn-air battery with Co-Nd2O3/NC-700 shows a high specific capacity of ∼613.6 mA h g−1Zn and superior charge-discharge cycling durability.

A new multi-functional crystal has been implemented by combining the acousto-optic (A/O) modulation with Raman laser output, which has never reported before. Notably, the α-BTM displaying an adequate A/O figure of merit of 10.18 × 10 -18 s 3 /g using the comparison method is originally tailored to fabricate an A/O modulator that exhibits a high diffraction angle and diffraction efficiency of 1.432° and 82.1% at 1064 nm, respectively, which can be competitive with that of TeO 2 . Pumped by a pulsed laser, sequentially, the self-Q-switch Raman laser working at 1178.1 nm is successfully realized based on α-BTM crystal. A maximum output power of 86 mW operating at 1178.1 nm and the repetition frequency of 15 kHz were obtained with the pump power of 27 W. Our works not only enrich the family of A/O materials, but also opens up a viable route towards exploiting the design of multi-functional crystal.

To alleviate the sluggish oxygen evolution reaction (OER) kinetics, it's urgent to develop electrocatalysts with high activity and low cost. In this work, Fe doped metal organic frameworks (Ni)/carbon black composites were synthesized via a facile hydrothermal method. Benefiting from the direct use of metal organic frameworks (MOFs) for OER, numerous and highly dispersed active sites are exposed to the electrolyte and reactants. By regulating Ni/Fe ratios, a high electrochemical active surface area (ECSA) and high relative surface content of active Ni3+ species are obtained, which mainly contribute to the high OER activity. Besides, the introduced carbon black (CB) was found to enhance the charge-transfer efficiency of the electrocatalysts, which is also favorable for OER. The optimal Ni9Fe1-BDC-0.15CB electrocatalyst shows excellent OER activity with the low overpotential of ~290 mV at 10 mA cm−2 and the Tafel slope of ~76.1 mV dec−1, which is comparable to RuO2 and other MOFs-based OER electrocatalysts reported in recent years.

A metal-organic framework-derived method was developed to synthesize highly efficient non-noble metal electrocatalyst for alkaline hydrogen evolution reaction (HER). Zn2+, phosphomolybdic acid were coordinated with 2-methylimidazole, and zinc (Zn) and phosphorus (P) species were removed by annealing at 850 °C in N2 atmosphere, resulting in micro/mesoporous molybdenum carbide (Mo2C) composited with nitrogen-doped carbon (denoted as ZIF8-xMo-850). The optimized sample ZIF8-12Mo-850 displayed a low overpotential of ~85.7 mV to deliver a current density of 10 mA cm−2, with a corresponding Tafel slope of ~69.7 mV dec−1 in 1 M KOH. This HER catalytic activity was competitive with the most recently developed Mo2C-based HER electrocatalysts. From further investigation, the high HER catalytic activity of ZIF8-12Mo-850 is owing to three aspects: (i) The appropriate Mo feeding amount of ZIF8-12Mo-850 resulted in the highest surface content of Mo2+ active site; (ii) The evaporation of Zn and P in the ZIF8-12Mo precursor formed its largest average pore diameter of 32.3 nm, which leaded to the highest electrochemically active surface area (ECSA) of 64.29 cm2 (iii) The 2-methylimidazole in the precursor resulted in the highest surface content of pyridinic N in ZIF8-12Mo-850 (14.63%), which efficiently improved its conductivity and charge transfer efficiency.

Non-noble-metal based materials with high activity for oxygen reduction reaction (ORR) are urgently required to substitute Pt-based materials. Herein, metallic Co/N-doped carbon electrocatalysts were synthesized via a facile pyrolysis method of bimetal ZIF(ZnCo)/polypyrrole-polyaniline (ppy-pani) precursors. The evaporation of Zn and the introduced ppy-pani can lead to the porous structure and effectively hinder the aggregation of Co species, which results in the small nanoparticles uniformly distributed on carbon matrices. A high ECSA and a high content of Co species are obtained after the introduction of ppy-pani, thus resulting in the abundant Co2+ species to enhance ORR. Therefore, the optimized ZIF/ppy-pani-750 exhibits a high E1/2 (~0.86 V) and a low Tafel slope (~43.6 mV dec−1).

The global NH3 production is dominated by Haber–Bosch process, requiring high temperature and pressure. Electrochemical N2 reduction reaction (NRR) under ambient conditions is a greener path for artificial N2 fixation to NH3 but calling for efficient catalyst to increase activity and selectivity. Herein, we report the iron-based metal–organic frameworks (MOFs), i.e., MIL-88B–Fe and amine-functionalized MIL-88B–Fe (NH2–MIL-88B–Fe) as efficient catalysts for electrochemical NRR under ambient temperature and pressure in neutral electrolyte. NH2–MIL-88B–Fe shows higher NH3 yield rate of 1.205 × 10–10 mol s−1 cm−2 than MIL-88B–Fe (3.575 × 10–11 mol s−1 cm−2). Furthermore, NH2–MIL-88B–Fe exhibits the highest Faradaic efficiency of 12.45% at 0.05 V versus RHE. The control experiments prove that NH3 is produced through electrocatalytic NRR. This work may trigger the interest of using MOFs as highly efficient catalysts for electrochemical NH3 production.

Two-dimensional (2D) mono-elemental materials (Xenes) show remarkable potential in the fields of fundamental science and technology, have been regarded as a wide range of building blocks for electronic technologies due to their unique chemical, physical, electrical, and optical properties. Here, 2D tellurene/black phosphorus (Te/BP) heterojunctions are successfully fabricated through liquid-phase exfoliation (LPE) method. Their nonlinear optical absorption properties at 1.0, 2.0, and 2.8 μm have been studied by an open-aperture Z-scan method. The results revealed the excellent broadband saturable absorption responses of the prepared BP/Te heterojunctions, which are further confirmed by using them as saturable absorbers (SAs) for passively Q-switched all-solid-state lasers operating at 1.0, 2.0, and 2.8 μm, respectively. In particular, 1.04 μm continuous-wave (CW) mode-locked lasers with a pulse width of 404 fs is realized for the first time, to our best knowledge. Our work indicates that 2D Xenes especially 2D Xenes based heterojunctions have great potential in the fields of pulsed laser generation/modulation and other optoelectronic and photonic devices.

Developing earth-abundant highly efficient catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is indispensable for the widespread implementation of electrochemical water splitting to store renewable energy. Herein, amorphous bimetallic selenide (Ni-Fe-Se) hollow nanospheres electrodeposited on nickel foam (Ni-Fe-Se/NF) are developed as a bifunctional catalyst for the HER and OER. The HER and OER bifunctional activity of Ni-Fe-Se/NF outperforms those of monometallic Ni-Se/NF and Fe-Se/NF owing to the synergy of Ni and Fe in Ni-Fe-Se/NF. Moreover, the amorphous hollow spherical morphology of Ni-Fe-Se/NF increases the active site density and facilitates the mass transfer of electrolytes and H2/O2 products. Ni-Fe-Se/NF drives a current density of 10 mA cm-2 with an overpotential of ∼85 mV for the HER and 100 mA cm-2 with an overpotential of ∼222 mV for the OER. As the HER and OER bifunctional catalyst, Ni-Fe-Se/NF can split alkaline water with total voltages of ∼1.52 V and ∼1.66 V at 10 mA cm-2 and 100 mA cm-2, respectively, and remain stable over 50 hours of operation in 1 M KOH.

This work develops CoNi alloys with slight oxidation@N,O co-doped carbon (NOC) as multifunctional catalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and Zn–air batteries. Their outer NOC shells have direct contributions to ORR, OER and HER activity that is dominated by N and O dopants that closely correlate with active adjacent C atoms. Meanwhile, the inner cores (CoNi alloys with slight oxidation) can provide indirect and important contributions. Relying on enhanced collective contributions of outer NOC shells and inner cores that are tuned by Co/Ni molar ratios, CoNi(1 : 1)-TB-800N2 with a Co/Ni molar ratio of 1 : 1 affords optimized multifunctional activity. Furthermore, it also brings about optimal Zn–air battery performance: ∼98.6% and ∼74.8% of theoretical specific capacity and energy density, respectively, and more than 100 h of stable charge–discharge operation at high current densities.

In this work, a series of metallic Co-ZnO encapsulated in N-doped carbon/carbon nanotubes (Co-ZnO@NC/CNT-T) for the electrochemical oxygen reduction reaction (ORR) were synthesized by annealing bimetallic metal-organic frameworks (MOFs) containing Co and Zn in N2 atmosphere. Within the hybrid, metallic Co was integrated with ZnO and encapsulated by NC, while coral-like CNTs grew out of the obtained Co-ZnO@NC nanoparticles. When applied in ORR catalysis, the optimized Co-ZnO@NC/CNT-700 obtained in 700 °C displayed a half-wave potential of ~0.86 V and a limiting current density of ~−5.98 mA cm−2, which were even superior to 20 wt% Pt/C. Further results demonstrated that the presence of ZnO was closely related with the high ORR catalytic activity from two aspects. (i) ZnO catalyzed the formation of Co0, Co2+, pyridinic and graphitic N as the main active species for ORR. (ii) ZnO promoted the growth of CNTs and micro/mesoporous structure, which improved the electrochemical active surface area (ECSA) and mass transfer during the ORR process.

In this work, electrochemical nitrogen reduction reaction (NRR) on metallic Co@N-doped carbon (NC) (Co@NC) were investigated. The Co@NC catalysts obtained via pyrolysis of a metal-organic framework precursor (ZIF-67) showed high Faraday efficiency under ambient conditions in neutral electrolytes. At −0.9 V versus Ag/AgCl, the Faraday efficiency of Co@NC achieved as high as 21.79%, surpassing most of reported catalysts under comparable conditions, while the NH3 yield rate of Co@NC reached 1.57 × 10−10 mol s−1 cm−2 at the same potential. This work demonstrated that Co@NC had outstanding electrocatalytic performance for NRR. Thus it was a promising transition-metal-based catalyst in electrochemical ammonia synthesis.

Molybdenum sulfide (MoS2) is considered as low-cost catalyst with great potential for hydrogen evolution reaction (HER). In this contribution, a promising Mo-precursor was first designed and prepar...

A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at $2.0~\mu \text{m}$ for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, $24.2~\mu \text{J}$ , and 80 W, respectively. The results are distinguished from other two-dimensional materials-based $2.0~\mu \text{m}$ PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the $2.0~\mu \text{m}$ spectral range.

In this work, a series of metallic cobalt-molybdenum carbide@graphitic carbon (CoMo(x:y)-T@GC) nanocomposites for the electrochemical hydrogen evolution reaction (HER) were synthesized by a sol-gel method. In the as-prepared nanocomposites, β-Mo2C and metallic Co coexisted and were encapsulated by graphitic carbon. The presence of metallic Co effectively enhanced the crystallinity of β-Mo2C, charge transfer efficiency and electrochemical active surface area (ECSA), thus resulting in the improved HER catalytic activities of the CoMo(x:y)-T@GC nanocomposites. The optimized electrocatalyst CoMo(0.5:0.5)-800@GC required the lowest overpotential of ∼165 mV to deliver a current density of 10 mA cm−2 in 0.1 M KOH, which was at the forefront compared with recently reported Mo2C-based electrocatalysts.

For van der Waals (vdW) heterostructures, optical and electrical properties ( e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS2 enable the graphene/MoS2 (G/MoS2) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS2 with different thicknesses of MoS2, and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS2 heterostructure interlayer coupling can be tuned by changing the thickness of MoS2, furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS2 heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump-probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS2 heterostructures with different MoS2 layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS2 heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS2 may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices.

Metal-organic frameworks (MOFs) are a series of highly porous crystalline materials, which are built from inorganic metal nodes and organic linkers through coordination bonds. Their unique porous structural features (such as high porosity, high surface areas, and highly ordered nanoporous structures) and designable structures and compositions have facilitated their use in gas capture, separation, catalysis, and energy storage and conversion. Recently, the design and synthesis of pure MOFs and their derivatives have opened new routes to develop highly efficient electrocatalysts toward oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), which are the core electrode reactions in many energy storage and conversion techniques, such as metal-air batteries and fuel cells. This review first discusses recent progress in the synthesis and the electrocatalytic applications of pure MOF-based electrocatalysts toward ORR or OER, including pure MOFs, MOFs decorated with active species, and MOFs incorporated with conductive materials. The following section focuses on the advancements of the design and preparation of various MOF-derived materials—such as inorganic nano- (or micro-) structures/porous carbon composites, pure porous carbons, pure inorganic nano- (or micro-) structured materials, and single-atom electrocatalysts—and their applications in oxygen electrocatalysis. Finally, we present a conclusion and an outlook for some general design strategies and future research directions of MOF-based oxygen electrocatalysts.

1T-titanium selenide (1T-TiSe2), a representative of 1T phase transition metal dichalcogenides (TMDs), exhibits semimetallic behaviour with a nearly zero bandgap structure, which makes it a promising photoelectric material. A high-quality multilayer 1T-TiSe2 saturable absorber (SA) is successfully fabricated by a combination of liquid phase exfoliation and the spin coating method. The broadband nonlinear saturable absorption properties of the prepared 1T-TiSe2 SA are investigated by using the open aperture (OA) Z-scan method. Passively Q-switched (PQS) all-solid-state lasers with different bulk crystals at the wavelengths of 1.0, 1.3, 2.0 and 2.8 μm are realised based on the 1T-TiSe2 SA. To the best of our knowledge, this is the first presentation of the application of a 1T-TiSe2 material to all-solid-state bulk lasers. The results indicate that 1T-TiSe2 could be an alternative broadband SA for solid-state pulsed lasers and exhibits promising potential applications in mode-locked ultrafast lasers.

Electrochemical nitrogen reduction reaction (NRR) is regarded as a promising route for ammonia synthesis, which still faces several challenges including NH3 yield and low selectivity. Herein, Zr-doped α-FeOOH (Zr/α-FeOOH) was developed as NRR electrocatalyst, which shows a high NH3 yield of 1.39 × 10−10 mol s−1 cm−2 and a significantly increased Faradaic efficiency (FE) of 35.63%. The Zr doping is found to induce more O vacancies as NRR active sites, which results in the increased NH3 yield. Besides, Zr species can suppress the competing side reaction effectively and have a positive effect on the high FE. Furthermore, the electrochemical in situ attenuated total reflection surface-enhanced infrared reflection absorption spectroscopy was conducted to investigate the NRR mechanism on Zr/α-FeOOH surface, which was revealed to follow an associative reaction pathway.

Electrolysis of water in alkaline media to produce hydrogen is a green and promising energy storage technology, but the kinetically sluggish hydrogen evolution reaction (HER) in alkaline electrolytes limits its development, requiring cheap and highly efficient catalysts to increase the HER rate. The HER activity of transition metal-based catalysts is closely associated with the d-band structures. Herein, the surface strain of Ni and NiO was engineered to regulate the d-band centers and the HER activity. DFT calculations found that the Ni(111) supported NiO(111) shows expanded surface lattice compared to the unsupported NiO(111), and the NiO(100) supported Ni(100) shows compressed surface lattice compared to the unsupported Ni(100), leading to ∼2 eV upshift and downshift of d-band centers of the surface Ni atoms, respectively. Guided by the DFT calculation, the surface-oxidized Ni (so-Ni) and surface-reduced NiO (sr-NiO) catalysts were synthesized and shows expanded and compressed surface lattice respectively, leading to enhanced HER activity. The synthesized sr-NiO shows the highest HER activity with an overpotential of 164 mV to deliver a current density of 10 mA cm−2, which outperforms many of the recently reported Ni-based HER catalysts in alkaline electrolytes.

Metal–organic-frameworks (MOFs) (i.e., MOF(Fe), MOF(Co) and MOF(Cu)) were synthesized by a hydrothermal process. The prepared MOFs were characterized using X-ray diffraction, Fourier transform infrared spectroscopy and N2 adsorption–desorption. The catalytic activities of the MOFs for the electrochemical synthesis of ammonia were evaluated when using N2 (air) and water as raw materials at low temperature and ambient pressure. The results indicated that the prepared MOFs have fine crystalline structures, abundant micropores, and large specific surface areas. The prepared MOFs showed excellent catalytic activity for the electrochemical synthesis of ammonia at low temperature and ambient pressure. Among these MOFs, the MOF(Fe) displayed the best catalytic activity, and the highest ammonia formation rate and the highest current efficiency reached 2.12 × 10−9 mol s−1 cm−2 and 1.43%, respectively, at 1.2 V and 90 °C, when using pure N2 and water as raw materials. The prepared MOFs in this work showed remarkable catalytic activities for the electrochemical synthesis of ammonia at low temperature and ambient pressure among the non-noble metal catalysts. It was the first exploration to apply MOFs as the electrocatalysts for the electrochemical synthesis of ammonia at low temperature and ambient pressure.

Stable passive mode-locking multi-segment composite Nd:GdVO 4 lasers with a semiconductor saturable absorber mirror were demonstrated for the first time. For the composite crystals, the output power increased linearly with the increase of the incident pump power, showing excellent thermo-mechanical performances. While for the conventional crystal, power saturation was observed when the incident pump power exceeded 8.79 W. The maximum average output power of 1.465 W was achieved by Nd(0.1%):GdVO 4 /Nd(0.5%):GdVO 4 /Nd(1%):GdVO 4 composite crystal at an incident pump power of 9.28 W. The largest pulse energy of 14.90 nJ and the highest peak power of 0.53 kW with a pulse duration of 28.0 ps were also obtained by using the same composite crystal, revealing that the multi-segment composite crystal with a proper combination of Nd 3+ -doped concentrations could obtain the optimal laser performance.

Here, few-layered W2C nanosheets and microfiber-based few-layered W2C-SA are fabricated by the magnetron sputtering deposition method. The third-order nonlinear optical responses of the prepared 2D W2C nanosheets are investigated by the Z-scan method with βeff and n2 determined to be −88.2 cm/MW and −1.112×10−13 m2/W, respectively, revealing its excellent nonlinear saturable absorption properties and optical modulation capabilities. In addition, by incorporating microfiber based few-layered W2C-SA into Yb-doped and Er-doped fiber lasers (YDFLs and EDFLs), the passively mode-locked operations at the central wavelength of 1035.1 and 1562 nm are realized, respectively. In addition, multi-soliton bound mode-locked operation in EDFLs with soliton pulses up to 36 is realized. Our results not only demonstrate the capability of few-layered W2C as a wideband optical modulator, but also provide a practical approach to explore soliton dynamics in fiber lasers.

Niobium carbide ( N b 2 C ), a novel two-dimensional MXene material, has attracted much attention due to its outstanding electronic and optical properties. In this work, a microfiber-based few-layer N b 2 C saturable absorber (SA) is fabricated by the magnetron sputtering deposition technique. The reverse saturable absorption (RSA) response of few-layer N b 2 C nanosheets is observed with I-scan measurements. The square-wave pulses (SWPs) are generated by using the as-prepared microfiber-based few-layer N b 2 C SA in an erbium-doped fiber laser. The SWP width increases from 0.33 to 2.061 ns with the single pulse energy increases linearly up to 0.89 nJ while the amplitude remains as a constant. In addition, nonlinear polarization rotation mode-locking fiber lasers with different cavity lengths are constructed to explore the formation conditions of SWP. Our results indicate that the RSA effect of the few-layer N b 2 C nanosheets plays a decisive role in the formation of the SWP.

In order to reduce the energy consumption of hydrogen evolution reaction (HER), a series of lanthanum-doped cobalt oxide (x%La–Co3O4–T, where x% represents the La doping molar ratio and T represents the annealing temperature) electrocatalysts are successfully synthesized by a co-precipitation process, followed by annealing in air. Through X-ray diffraction (XRD) refinements, La3+ is doped into Co3O4 lattice, which decreases the crystallinity of Co3O4. It inhibits the aggregation and growth of Co3O4 grains. 2%La–Co3O4-350 is the optimized sample to show the lowest overpotential of 98 mV at 10 mA cm−2 with the corresponding Tafel slope of 72.8 mV dec−1 in 1 M KOH. Although La is an inactive rare-earth metal element for HER, it enhances the HER activity of Co3O4 efficiently. From further studies, the high HER catalytic activity of 2%La–Co3O4-350 can be owing to three aspects: (i) The highly dispersed and small-size Co3O4 nanoparticles caused by La doping own high specific surface area and electrochemically active surface area (ECSA), which benefits exposing more Co3+ active sites to electrolyte. (ii) La dopants make 2%La–Co3O4-350 own more oxygen vacancies that facilitating the water dissociation step of HER. (iii) La doping leads to improved conductivity and charge transfer efficiency of 2%La–Co3O4-350 during HER.

A diode-pumped Tm,Ho:YAP laser utilizing a self-made LiNbO 3 (LN) electro-optically modulator (EOM) at room temperature is demonstrated for the first time. A minimum pulse duration of 107.4 ns was obtained at a pulse repetition rate (PRR) of 200 Hz, giving a maximum single pulse energy of 1.65 mJ. At a PRR of 1 kHz, pulse duration of 145.8 ns was achieved under the absorbed pump power of 7.4 W, corresponding to a maximum single pulse energy of 0.546 mJ, and the pulse to pulse amplitude instabilities were measured to be about 4.6% and 5.83% for PRRs of 200 Hz and 1 kHz, respectively.

Diode-pumped dual-wavelength a-cut Nd:MgO:LiNbO3 lasers near 1085 and 1093 nm were experimentally and theoretically investigated. The simultaneous dual-wavelength emitting was mainly attributed to the Boltzmann distribution of the occupation in the Stark-split energy-levels in manifold 4I11/2. Under an absorbed pump power of 7.45 W, a maximum continuous wave (CW) output power of 1.23 W was obtained, giving a slope efficiency of 21.2%. Using Cr:YAG as saturable absorber, the shortest pulse duration of 28 ns was obtained with a repetition rate of 24 kHz, resulting in a peak power of 729 W.

Characteristics of diode-wing-pumped highly efficient Tm:LuAG lasers running both in continuous wave (CW) and electro-optical Q-switching regimes have been investigated. Using a simple plane-plane cavity, a maximum CW output power of 8.5 W has been achieved with a corresponding slope efficiency of 44.5% by “wing pumping” at 790 nm. With a V-shaped cavity, a diode-wing-pumped MgO:LiNbO3 crystal based electro-optically Q-switched Tm:LuAG laser at 2022.9 nm delivered a maximum pulse energy of 10.8 mJ and a minimum pulse width of 52 ns at a corresponding repetition rate of 100 Hz. To the best of our knowledge, the achieved CW output power and Q-switched pulse energy have both set records for all-solid-state Tm:LuAG lasers, which well reveals an efficient way to generate high-power and high-energy lasers at 2 μm wavelength.

Microfibers with different waist diameters were prepared successfully by a flame-brushing technique. Their saturable absorption properties were investigated. The non-saturable loss and modulation depth both decreased with the increase of the diameter. According to the mode distribution of microfibers with a waist diameter of 25 μm, it could be supposed that the evanescent field effect may be useful for microfibers being saturable absorbers (SAs). Based on the 25 μm-diameter microfiber, an all-fiber-structure mode-locked fiber laser was achieved successfully with long term stability in the span of a week. The results indicated that microfibers with suitable diameters were excellent SAs. To the best of our knowledge, this is first report on the usage of microfibers as a SA for building ultrafast fiber lasers.

An electro-optical modulator (EOM) made of a z -cut LiNbO 3 (LN) crystal with size of 9×9×25 mm 3 was designed to work in transverse-field regime. The extinction ratio of the EOM was measured to be 324:1. With the EOM operating in off Q-switching regime, a diode pumped all-solid-state actively Q-switched Tm:LuAG laser at 2 μm was realized. At repetition rate of 200 Hz, 2.5 mJ pulses with duration of 88.2 ns were generated. A maximum pulse energy of 2.51 mJ was achieved at repetition rate of 50 Hz, corresponding to a minimum pulse duration of 88 ns.

Diode-pumped CW and passively Q-switched Nd:LuLiF 4 lasers with stable, synchronous dual-wavelength operations near 1047 and 1053 nm were demonstrated for the first time. The maximal CW output power of 821 mW was obtained at an incident pump power of 6.52 W. Employing high quality Bi-doped GaAs as saturable absorber, stable dual-wavelength Q-switched operation was realized. Under 6.52 W incident pump power, the minimal pulse duration of 1.5 ns, the largest single pulse energy of 11.32 μJ, and the highest peak power of 7.25 kW were achieved.

By simultaneously using a multi-walled carbon nanotube (MWCNT) and a monolayer graphene saturable absorber (SA) in the cavity, a laser-diode-pumped dual-loss-modulated passively Q-switched Tm:LuAG laser at 2 mu m is demonstrated for the first time. In comparison with the singly passively Q-switched laser with MWCNT or monolayer graphene SA, the doubly passively Q-switched laser with both MWCNT and monolayer graphene SA can generate shorter pulse width and higher peak power. A maximum pulse width compression ratio of 2.8 and a highest peak power enhancement factor of 4 were obtained at the incident pump power of 5.8 W, respectively. The experimental results show that the dual-loss modulation is an efficient method to compress the pulse widths and improve the peak powers of the Q-switched lasers at 2 mu m.

By using monolayer graphene as saturable absorber, a passively Q-switched Tm:LuAG laser with high efficiency at 2 μm is demonstrated. At the incident pump power of 5.8 W, pulses with duration of 235 ns and maximum average output power of 873 mW were obtained at a repetition rate of 72 kHz. This is, to the best of our knowledge, the highest average output power, as well as the narrowest pulse width, ever obtained among graphene-based passively Q-switched solid-state bulk lasers at 2 μm regime.

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta2NiS5 with a narrow bandgap, has been successfully fabricated and used as a SA in a 1.9 μm spectral region. The nonlinear saturable absorption properties of the as-prepared SA have been investigated by using an open-aperture Z-scan method. A passively Q-switched all-solid-state laser operating at 1.9 μm has been realized with the Ta2NiS5 SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the passively Q-switched (PQS) laser are 1.1 W, 313 ns, 22.0 μJ, and 71.0 W, respectively. This is the first demonstration of the saturable absorption property of Ta2NiS5, to the best of our knowledge. The results indicate well the promising potential of Ta2NiS5 as a broadband SA in realizing pulsed mid-infrared lasers with high performance.

A saturable absorber (SA) based on molybdenum sulfoselenide (MoSSe) was fabricated using a combination of liquid exfoliation and laser deposition methods. A dual-wavelength passively Q-switched Er-doped fiber laser (EDFL) was fabricated by inserting the MoSSe-SA into a ring cavity. The maximum average output power was 23.4 mW. The pulse width decreased from 2.8 to 1.78 μs while the corresponding pulse repetition rate increased from 50 to 90 kHz. To the best of our knowledge, this is the first report on a passively Q-switched EDFL based on a MoSSe-SA operating at 1.5 μm. Our results indicate that MoSSe-like three-element transition-metal dichalcogenides could be a promising alternative optical modulators for pulsed fiber laser generation.

The mode-locked performances of composite and conventional Nd:YVO 4 crystals were demonstrated with a semiconductor saturable absorber mirror. For the conventional crystal, power saturation was observed when the pump power exceeded 5.31 W, while for the composite crystals, the output power increased linearly with the pump power, showing good thermo-mechanical performances. The maximum average output power of 1.2 W was achieved by a composite crystal at an incident pump power of 7.09 W. The largest pulse energy of 34.6 nJ and the highest peak power of 4.9 kW with a pulse duration of 7 ps were also obtained by the same composite crystal while the non-composite crystal got the shortest pulse duration of 5.3 ps. The theoretical analysis on pulse duration for different laser media is in agreement with the experimental result.

Organic–inorganic hybrid membranes based on poly(methyl methacrylate) (PMMA)/silica have been synthesized using a sol-gel technique for use in polymer electrolyte fuel cells (PEFCs). The properties of these membranes were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis. The results indicate that these membranes are formed through hydrogen bonds between the carbonyl group of PMMA and the uncondensed alcohol functional groups of the inorganic clusters. The proton conductivity of these membranes is on the order of 10 −1 S cm −1 , and the 60PMMA–30SiO 2 –10P 2 O 5 membrane displays the highest proton conductivity of 3.85 × 10 −1 S cm −1 at 90 °C and 50% RH. The performance of a fuel cell using these membranes was tested. A maximum power density of 370 mW cm −2 is obtained at 80 °C, and the current density at 0.4 V remains almost unchanged during the 100-h test time under the test conditions. This class of hybrid membranes is an extremely promising material for use in PEFCs.

Using electro-optic (EO) modulator and GaAs saturable absorber, a diode-pumped doubly Q-switched and mode-locked (QML) YVO4/Nd:YVO4 laser at 1.06 μm is realized. The experimental results show that the number of the mode-locking pulses underneath the Q-switched envelope decreased with increasing pump power. With an output coupling of 6.5 %, the single mode-locking pulse underneath the Q-switched envelope with 1 kHz repetition rate was obtained when the pump power exceeded 4.65 W. At a pump power of 8.25 W for an output coupling of 10 %, a stable mode-locking pulse train at a repetition rate of 1 kHz was achieved with pulse energy as high as 582 μJ and pulse duration of about 580 ps, corresponding to a peak power of 1 MW. Using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled rate equations for diode-pumped doubly QML YVO4/Nd:YVO4 laser are given and the numerical solutions of the equations are basically in accordance with the experimental results.

The hybrid Q-switched and mode-locked (QML) operation of Nd:Lu0.15Y0.85VO4 crystal at 1.34 μm with V:YAG saturable absorber and acousto-optic (AO) modulator has been realized. The laser characteristics are distinctly improved by the hybrid QML if compared to those with the single V:YAG QML. At the pump power of 5.04 W, the Q-switched pulse energy is enlarged to 5.6 times and the Q-switched pulse width is shortened to 40% by the AO modulator in contrast to those of the single passively QML.

By simultaneously using an electro-optic (EO) modulator and a single-walled carbon nanotube saturable absorber (SWCNT-SA) in the cavity, a diode-pumped doubly Q-switched Nd:Lu0.33Y0.37Gd0.3VO4 (Nd:LuYGdVO4) laser is demonstrated. At the incident pump power 11.43 W and f=2 kHz, the minimum pulse width 17.6 ns and the maximum pulse peak power 19,886 W can be obtained. The experimental results show that this doubly Q-switched Nd:LuYGdVO4 laser can generate shorter pulse width and higher peak power compared to the singly Q-switched Nd:LuYGdVO4 laser with only EO or SWCNT-SA.

By using double-mixed crystal Nd:Lu0.15Y0.85VO4 as laser medium, a diode-pumped doubly Q-switched and mode-locked (QML) Nd:Lu0.15Y0.85VO4 laser with acousto-optic (AO) modulator and central semiconductor saturable absorption mirror (SESAM) is realized for the first time. The Q-switched envelope modulation depth is nearly 100%.The average output power and the pulse width of the Q-switched envelope etc. for different AO modulator repetition rates have been measured. The experimental result show that Nd:Lu0.15Y0.85VO4 crystal is an excellent laser medium for doubly QML lasers.

Two graphene oxide saturable absorbers (GO-SAs) spin coated on indium tin oxide (ITO) substrate have been prepared and their transmissivity spectra have also been measured. The performance of the diode-pumped passively Q-switched Nd:YVO4 laser with GO-SA has been investigated for the first time. The shortest pulse width of 113 ns and the highest peak power of 4.3 W are obtained at the pump power of 5.04 W. The output laser characteristics have demonstrated that graphene oxide is a promising saturable absorber for passive Q-switching.

By using acousto-optic (AO) modulator as active Q-switch, the diode-pumped actively Q-switched Nd:Lu0.15Y0.85VO4 and Nd:Lu0.33Y0.37Gd0.3VO4 lasers are realized. The average output power and the pulse width under different AO repetition rates are measured. The actively Q-switched laser performances for two kind mixed crystals are compared for the first time. The experimental results show that the actively Q-switched Nd:Lu0.33Y0.37Gd0.3VO4 laser can generate shorter pulse width with higher peak power in comparison with the actively Q-switched Nd:Lu0.15Y0.85VO4 laser. Due to broader fluorescence line-width, the triple-mixed crystal Nd:Lu0.33Y0.37Gd0.3VO4 is a promising laser medium for shorter Q-switched pulse with higher peak power.

A diode-pumped dual-loss-modulated Q-switched and mode-locked (QML) Nd:Lu0.15Y0.85VO4 laser at 1.34 μm with single-walled carbon nanotube saturable absorber (SWCNT-SA) and acousto-optic (AO) modulator is demonstrated. The modulation depth of the dual-loss-modulated QML laser reaches 90%, being deeper than 75% that obtained by the single passively QML laser. The stability of the hybrid QML laser is significantly improved if compared to that only with SWCNT-SA. The Q-switched pulse energy and the Q-switched pulse width of the QML laser with the dual-loss-modulation are 487 and 27% of those only with SWCNT-SA, respectively.

By using a piece of single-walled carbon nanotube saturable absorber, the performance of the passively Q-switched composite Nd:YVO4 laser has been demonstrated for the first time. The maximum average output power and the shortest pulse width are 1220 mW and 103 ns at the incident pump power of 5.04 W for a 10% transmission of the output coupler. The highest pulse repetition rate of 415.6 kHz and the largest single-pulse energy of 2.94 μJ are also obtained. The composite Nd:YVO4 crystal has more excellent laser performance than the normal Nd:YVO4 crystal at 1064 nm.

Diode pumped continuous wave operation and passively Q-switched performances of a Nd:Sc2SiO5 laser crystal at 1.08 microns have been demonstrated. A maximum continuous wave average output power up to 1.86 W has been obtained, corresponding to an optical conversion efficiency of 20.7% and a slope efficiency of 30.4% with respect to the absorbed pump power. With a Cr4+:YAG wafer used as the saturable absorber, a passively Q-switched Nd:Sc2SiO5 laser generated a pulse as short as 22.5 ns at a repetition rate of 20 kHz. The maximum pulse energy of 44.8 μJ was achieved, corresponding to a maximum pulse peak power of 1.66 kW.