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Nitrogen-doped graphite-encapsulated cobalt nanoparticles (Co@G NPs) were fabricated via a one-step arc-discharge method. The core/shell nanostructure and surface functionality were tailored by changing the ammonia content in the working gas mixture. Specifically, the average core diameter changed from 5 to 23 nm, average graphite shell thickness from 1.5 to 3.5 nm as the NH3 ratio increased from 0% to 20%. All these arc products exhibited better microwave absorption properties than the pristine Co micro powders. Co@G NPs prepared with 5% of NH3 presented 1.5 at.% of surface doping nitrogen, showing the optimal reflection loss (RL) value of −37.70 dB at the thickness of 5 mm. For the products prepared with 12.5% of NH3, wide absorption bandwidths of 5.60 GHz (RL

Highly concentrated amino group-modified biochars derived from twelve biomass residuals are achieved using a two-step radio-frequency Ar/NH3 plasma. The dependence of amino number, N bonding states, surface defects on the pretreatment time of Ar plasma, post-treatment power, duration and gas ratio are well established. For bamboo-biochar, the amino number and N content reach the maximum (8.04 × 1016/mg of biochar, 8.84 at.%) at 8.0% NH3 in NH3/Ar, presenting a highly consistent variation tendency with the emission intensity of NH radical. Notably, micropores can be created in matrix by the processing of plasma in moderate conditions, i.e., a given pretreatment time (e.g., 12.5 min), specific gas ratios of post-treatment (≥50% of NH3) at high RF power (e.g., 240 W) and proper duration (≤15.0 min). The uptake capacities of Pb(II) (123.1 mg g−1), Cu(II) (98.5 mg g−1) and Cd(II) (61.2 mg g−1) on aminated biochars are 5.42, 5.38 and 7.56 times higher than those on raw biochars. This study shows attractive prospects for the fundamental research in powder modification as well as potentials in environmental management.

Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions (RE3+) doped upconversion (UC) materials is still desirable. In this work, the intense single-band red emission is achieved by co-doping only Ho3+ in the BiOCl: Er3+ under 1550 nm excitation. In the BiOCl layered host, co-doping Ho3+ can further enhance the red emission and simultaneously suppress the green emission of Er3+, and thus obviously improve the red-to-green (R/G) ratio. It is found that Ho3+ does not serve as energy trapping through the 5I6 state as in traditional UC materials but acts as ET bridge (4S3/2, 2H11/2 (Er3+) → 5F4, 5S2 (Ho3+) → 4F9/2 (Er3+)). The tuning mechanism of Ho3+ is discussed in detail and further confirms through a comparative experiment. Our research gives an unusual perspective to tune the UC behavior of Er3+ through co-doping Ho3+, which might be inspiring for achievement of single-band red UC emission.

Substitutional heterovalent doping has been an effective method to manipulate the optical properties of Lanthanide-doped phosphors in the past. Herein, we report a new strategy of nonmetal atom carbon dopant in BiOCl nanosheets for tailoring the electric dipole transitions (EDTs) of Eu3+ ions, in which photoferroelectric effect (PFE) play a crucial role rather than the traditional lattice modification. Experimental results and first-principles calculations provide evidence that the replacement of C ions for Cl gives rise to strengthen macroscopic polarization and spontaneous inter electric field (IEF) of BiOCl. Under interband excitation, the enhanced PFE triggered by the IEF generated higher photopolarzition field and carrier separation efficiency. Consequently, the intensity ratio of 5D0-7F4/5D0-7F2 transition of Eu3+ ion was enhanced significantly due to environmental sensitivity of EDTs, accompanying with prolonged decaytimes. However, under intraband excitation where no PFE occurs, all of these factors exhibit the opposite tendency with the increase of C dopants. The result of our work shows that the tunable PFE via C-heterovalent doping in the layered BiOCl host offer a new method that utilize the light-matter interactions to modify the PL properties of rare-earth (RE) ion doped materials.

A heating-induced monotonous increase in the Yb3+ excited state (2F5/2) lifetimes is found in Yb3+ single doped Bi7F11O5 nanocrystals, possibly due to the thermal-enhanced photocarrier separation in polarized layered semiconductors with spontaneous internal electric fields. This unique phenomenon is evaluated for its thermometric performance in terms of lifetime luminescence thermometry, and the maximum absolute/relative temperature sensitivity (Sa/Sr) reaches as high as 0.65 μs K−1/0.24% K−1 in biological temperature regions. The results of this work can offer great potential for lifetime luminescence thermometry in biological areas and provide ideas for designing efficient photonic and photoelectric thermal devices.

Neural interface is a critical component for the communication between the central nervous system and outside devices. But neural tissues withstand constant mechanical activity with outside devices...

Due to the wide range of anisotropic properties, layered hosts that consist of two-dimensional (2D) platelets may endow the upconversion (UC) of rare-earth ions (RE3+) dopants with new optical properties different to traditional three-dimensional (3D) host. Here, we first reported a different UC construction mechanism of Er3+ ions triggered by Bi9V2O18Cl layered crystal that combines spontaneous polarization and narrow-bandgap. The solid-method prepared Er3+-doped Bi9V2O18Cl crystals that are connected by van der wars forces present individual micro-sheet and significant polarization property. Over the threshold power of a commercial 980 nm laser, a special two-photon near-infrared (NIR) emission of 4I13/2 level in Er3+ ions are observed without concentration dependence, accompanied by a special UC process that upconverting photon number of red emission is always over that of the green one. Experiment indicant that under the spontaneous inter electric field (IEF), efficient photocarriers separation in the narrow band-gap semiconductor makes a special band-to-band multi-photon process of Er3+ ions possible, being responsible for the unusual multi-photon NIR and UC appearance. The results of this study can provide new insights into the relationship between the material structure and UC of RE3+ ions and promote the potential applications of photon avalanche phosphors in solid-state lasers and optical switches.

Substitutional heterovalent doping has been considered as an effective method to control optical properties of lanthanide doped phosphors in the past, but it focuses only on three-dimensional and insulating crystal hosts. This study aimed to report the efficient upconversion enhancement of Er3+ induced by a new strategy of Ca2+ heterovalent doping in the layered semiconducting host based on BiOCl crystals concentrated by van der Waals force. The surface photovoltage (SPV) tests, theoretical calculations and optical probing effect of Eu3+ ions provided evidence that the replacement of Bi3+ with Ca2+ strengthened the macroscopic polarization and the corresponding spontaneous internal electric field (IEF) along the [001] of the BiOCl crystal sheet. The upconversion (UC) red and green emission intensities of the sample co-doped with 10 mol% Ca2+ ions were enhanced 39 and 12 times, respectively, compared with those of the Ca2+-free sample. Moreover, this study showed that the higher separation efficiency of photocarriers led to the prolongation of the decay time of excited energy levels under the strengthened intrinsic IEF by Ca2+-heterovalent doping, which was partially responsible for the UC photoluminescence (PL) enhancement of Er3+. This work not only provided new insight into the method for the engineering of UC emissions but also enhanced the understanding of layered semiconducting materials to modify the transition of lanthanide ions.

In this work, we report a new optical properties and modification methods for the rare-earth (RE) ion doped upconversion (UC) materials. Here, The Yb3+- Eu3+ co-doped BiOCl layered micrometer crystals were synthesized via the traditional solid state reaction. The experiment results show that due to efficient photocarrier space separation role of IEF, a band-to-band multiphoton excitation process of Yb3+ ions and the subsequent photopolarization role have been triggered inside BiOCl crystals via a commercial 980 nm laser. Then, it combines the photopolarization electric field (PPF) of the laser beam to generate a multiplexed tunable photopolarization on the Eu3+ ions. Consequently, the uponverting Stark splitting and emission intensity ratio of electrical dipole transitions (EDTs) of Eu3+ ions could be tailored simultaneously, either by pumping power or Yb3+ ion doping level, but showing an opposite trend. This research provides new insights into the interaction between the light and materials as well as the UC tailored method of lanthanide ions, which may inspire the design of opto-electric multifunctional devices.

Under 980 nm excitation, bright visible upconversion (UC) photon avalanche (PA) luminescence as well as 1560 nm near infrared (NIR) emission with looping behavior have been generated from Er3+-doped BiOCl nanosheets synthesized by solvent-thermal method. On tuning the surfactant addition, solvent content and pH value in synthesis, the cycle numbers for the UC and NIR PA processes could be modified accordingly. Comprehensive investigation indicated that the PA behaviors were initiated by the intense Raman vibration models due to Er3+ doping, which could be greatly intensified and modify the PA behaviors consequently when the synthesis conditions change the orientation of BiOCl nanosheets.

The upconversion of near-infrared (NIR) fluorescence, with a high tissue penetration depth, possesses a distinct advantage in biological temperature detection but is limited by the lack of rare earth-doped nanophosphors with intense and selective NIR UC emission. Here, we show that high-efficiency NIR temperature sensing can be achieved by appropriately doping Tm3+ activators into a polarized layered host, utilizing the high environmental sensitivity of the 3H4→3H6 electric dipole transition (808 nm) of Tm3+. To confirm this concept, Yb3+/Tm3+ codoped Bi7F11O5 upconverting nanosheets were synthesized and characterized. Furthermore, the thermometric performance of the samples was analyzed based on the temperature-dependent fluorescence intensity ratio from the thermally coupled levels (3F3/3H4) of Tm3+. The results showed that, under 980 nm diode laser excitation, the prepared samples can produce a high NIR-to-visible UC emission ratio (I800nm/I475nm) of over 2000 for Tm3+. The maximum sensitivity Sa/Sr was 1.4% K−1/0.577 K−1 at 303 K based on the 3F3 and 3H4 levels, and the material exhibited a wide functional temperature range of 303–573 K. The results of our work not only improve the understanding of the optical properties of RE3+ ions in layered materials but also show a potential application for physiological temperature sensing in biological tissues and cells.

In this work, under excitation at 808 nm, not only an unusual dominant emission of 2I11/2 → 4I15/2 transition (1.0 μm) but also the relatively weaker 1.55 μm luminesce (2I13/2 → 4I15/2) of Er3+ ions are observed with multi-phonon process and optical bistability behavior simultaneously for the first time. The bistability loops exhibit uniformly clockwise cycle characterized by a relatively lower trace of emission intensity at decreasing pump power. The result show that the looping behavior of NIR emissions has been found to be related to the 808 nm excited multi-photon band transition of BiOCl. Temperature sensing behavior of Er3+ indicate that such bistability effect is associated with thermally enhanced nonradiative decay and reduced luminescence quantum yield due to the strong pump-induced local thermal loading. This work may offer a novel insight into the transition behavior of lanthanides in layered semiconductors and promote the potential applications in optical switchers and temperature sensing.

The efficient extraction of uranium is challenging for radioactive wastewater treatment. Concerning to the specific coordination of functional groups with radionuclides, the development of ideal sorbents with high surface area, enhanced porosity and abundant functional groups compatibly to uptake uranium selectively is of great significance. Biochar, an attractive material to concentration aquatic targets, exhibits a positive correlation of surface area and pore volume of biochars with pyrolysis temperature, whereas a negative relation of surface functionality with thermolysis temperature. Here we applied a facile and environmental-friendly ball-milling technique to engineer raw biochars in the presence of phytic acid. Ball-milling treatment increased the external surface area of biochars by reducing grain sizes, as well as enhanced the micropore surface area by exposing blocked micropore networks. P-containing moiety was grafted to the surface of biochar matrix successfully. The physicochemical characteristics of biochars enabled a high uptake capacity (128.5 mg/g) and favorable selectivity of U(VI). It suggested that ball-milling of raw biochars with activating solvents could achieve an excellent performance for the efficient concentration of aquatic uranium.

Properly engineering of surface functionality and structural porosity is critical to improve the sorption performance of biochars. Herein, we report a facile one-pot preparation of phosphate group-functionalized biochars (PBs) derived from bamboo sawdust by engineering with phytic acid prior to pyrolysis. High specific surface areas (629, 1298 and 1109 m2·g−1), large pore volumes (0.332, 0.919 and 0.789 cm3·g−1), and abundant phosphorous contents (1.14, 3.32 and 1.53 at.%) are achieved compatibly for the PBs pyrolyzed at given temperatures (i.e., 300, 450 and 600 °C) which are significantly higher than those of pristine biochars. Phytic acid not only releases hydrogen protons to tailor biochar matrixes to make micropores created and further developed, but also provides organic phosphorous-containing moiety to guarantee the surface phosphate functionality. PBs extract U(VI) from aqueous media efficiently, i.e., equilibrium achieved within 8 h, high sorption capacity of 229.2 mg·g−1 (at pH 4.0, T 298 K), and favorable selectivity towards U(VI) against the interference of coexisting metal ions. PBs can be regenerated by 0.1 mol·L−1 Na2CO3 and reused well after six recycles. This present work provides a path for the design and synthesis of advanced biochars with favorable potentials in the extraction of U(VI)-containing effluents.

Bohai offshore oilfield in China is characterized by high oil viscosity, strong reservoir heterogeneity and big inter-well distances, which leads to the breakthrough of injection water in deep reservoirs with poor sweep efficiency and development effect. To solve this problem, this paper evaluated the performance of self-adaptive microgel system (SMG), and introduced its application in field trial.The self-adaptive microgel is a kind of microsphere in various sizes with strong deformation ability. In this paper, the physical and chemical properties of the self-adaptive microgel are studied by means of metallographic microscope and the statistical principle. Also, the extreme permeability value of the self-adaptive microgel which allows it to flow though the core is determined through core flow experiments and the evaluation method of resistance factor and residual resistance factor. Furthermore, a long core is used to evaluate the fluid diversion ability of the self-adaptive microgel under the condition of constant speed and constant pressure flooding. Finally, a field trial case study of the self-adaptive microgel is analyzed.Experiment results suggest that the self-adaptive microgel has good water swelling properties, narrow particle size distribution, huge inaccessible pore volume and large accessible pore volume of its carrier fluid. When the self-adaptive microgel with micron and submillimeter particle size flow through the core and the injection pressure stays stable, the permeability limit is 237×10−3μm2 and 712×10−3μm2, respectively. Since the self-adaptive microgel enters larger pores and generates plugging effect, while its carrier liquid enters smaller pores and displaces oil. So it obtains combined effects of "plugging" and "flooding". Moreover, the oil increment of the self-adaptive microgel under constant pressure flooding is higher than that under constant speed flooding. The case study shows that self-adaptive microgel flooding can increase oil production and reduce water cut obviously, which obtains technical and economic success.Also, this paper preliminarily establishes a property evaluation method for the self-adaptive microgel, analyzes its mechanism and displacement effect. Furthermore, the field trial effect of self-adaptive microgel flooding is explored. In summary, the research results provide a theoretical basis and technical support for the application of self-adaptive microgel flooding technology.