Plasmon-Assisted Self-Encrypted All-Optical Memory

All-optical responsive nanomaterials, which can rapidly switch between two stable states, have been regarded as the next-generation memories due to their potential to realize binary information storage and implement on-chip, integrated photonic neuromorphic systems. Rare earth oxides are preeminent candidates owing to their extraordinary luminescent stability and narrow optical transitions. However, due to the lack of simple and effective optical switches, it is difficult to realize all-optical data storage, encoding, and retrieval by pure rare earth-doped luminescent nanoparticles. Here, a rapid and high-contrast of 10⁴ luminescent switching of Y₂O₃:Eu³⁺ nanoparticle between the enhancement and quenching states is achieved by employing the strong light confinement and ultrafast thermal response of localized surface plasmon resonance. A self-encrypted all-optical memory is presented with optical information writing, encryption, reading, and re-writing, and a high-sensitivity synaptic response of emitters to frequency and light intensity flux, which can be harnessed to encrypt information flows and promote convenient and high-security information encryption. Such a convenient and secure plasmonic thermally assisted self-encrypting luminescent switch paves the way for constructing high-performance stimuli-responsive rare earth oxide crystals on demand and expanding their applications in various data encryption, anti-counterfeiting, and rewritable colouration devices.     

Organometallic L-Alanine Cadmium Iodide Crystals for Optical Device Fabrication

Single crystals of L-alanine cadmium iodide (LACI) were grown by the slow evaporation technique at room temperature. A single-crystal X-ray diffraction (SXRD) model was used to evaluate the crystal structure of the as-grown LACI crystal. The energy dispersive X-ray (EDX) analysis and ultraviolet-visible-near infrared (UV-vis-NIR) transmittance studies were carried out, and the results reveal the presence of elements in the title compound. From the transmittance data, the optical bandgap as a function of photon energy was estimated, and the different optical constants were calculated. A fluorescence study was performed for the LACI crystal. Thermogravimetric and differential thermal analyses have also been studied to investigate the thermal property of the LACI crystal. The efficiency of the second harmonic generation (SHG) of the title crystal was investigated. The magnetic and electrical properties were estimated by the vibrating sample magnetometer (VSM) analysis and impedance study, respectively.     

Single particle tracking of fluorescent nanodiamonds in cells and organisms

Ever since the discovery of fullerenes in 1985, nanocarbon has demonstrated a wide range of applications in various areas of science and engineering. Compared with metal, oxide, and semiconductor nanoparticles, the carbon-based nanomaterials have distinct advantages in both biotechnological and biomedical applications due to their inherent biocompatibility. Fluorescent nanodiamond (FND) joined the nanocarbon family in 2005. It was initially developed as a contrast agent for bioimaging because it can emit bright red photoluminescence from negatively charged nitrogen-vacancy centers built in the diamond matrix. A notable application of this technology is to study the cytoplasmic dynamics of living cells by tracking single bioconjugated FNDs in intracellular medium. This article provides a critical review on recent advances and developments of such single particle tracking (SPT) research. It summarizes SPT and related studies of FNDs in cells (such as cancer cell lines) and organisms (including zebrafish embryos, fruit fly embryos, whole nematodes, and mice) using assorted imaging techniques.     

Numerical and experimental investigation of the mesoscale fracture behaviour of quenched steels

During heat treatment processes, especially during quenching, cracks may form because of the presence of high thermal and mechanical stresses and strains. Notwithstanding the fact that increasingly detailed modelling for heat treatment is being performed (considering, i.a., grain size, creep and transformation plasticity), homogeneous microstructures are still normally assumed. Chemical and hence structural inhomogeneities are not commonly explicitly considered, which is especially accentuated in the case of real parts simulation because of the resulting numerical problem's size. Intensive quenching on a cylindrical specimen of 100Cr6 (SAE) steel is proposed here to experimentally investigate the microcrack generation. A finite element based model is proposed to numerically evaluate the fracture behaviour in a two‐step simulation. First, by solving the quenching problem in direct correspondance with the experimental test performed, and second, by studying the mesoscale response taking into account the influence of second phase particles in a representative volume element based approach. The maximum principal stress criterion is used to trigger the fracture by means of the extended finite element method at the mesoscale. The trend to form cracks in the surface region, experimentally observed, has been well captured by the model. The influence of carbides sizes and content on the mesoscale fracture response has been numerically analysed as well. A good agreement has been reached between the simulations and the experimental results, exhibiting the potential of the introduced approach to be used as a failure prediction methodology.     

磷光粉表面包覆对铜基磷光复合材料发光及摩擦性能影响

选用热稳定性好的SiO2为包覆物,采用溶胶-凝胶法,以正硅酸乙酯为硅源,对商用磷光粉SrAl2O4∶Eu2+,Dy3+表面进行包覆,以解决磷光粉在高温下制备复合材料过程中因与金属粒子接触以及高温氧化产生猝灭的问题。实验通过热压烧结制备块体铜基磷光复合材料,考评包覆工艺对高温下制备的复合材料发光及摩擦性能的影响。通过X射线衍射、扫描电镜、荧光分光仪等设备对包覆前后磷光粉的表面形貌和发光性能进行分析和表征,采用摩擦试验机对包覆前后磷光粉与高铝青铜粉末混合制备复合材料烧结试样的摩擦性能进行研究。结果表明磷光粉表面包覆可有效避免其在高温下氧化猝灭和接触猝灭,包覆后磷光粉应用于铜基复合材料中可有效降低复合材料的磨损量,提高材料的耐磨性,当包覆比为10%时复合材料的发光性能、耐磨损性能最佳。     

淬火速率对汽车用高强铝合金性能的影响

采用力学性能测试、电导率测试和透射电子显微镜研究了淬火速率对汽车用高强铝合金性能的影响。结果表明：淬火速率从960℃/s降低到1.8℃/s,电导率提高了5.7% IACS,硬度的下降率为40%,抗拉强度和屈服强度的下降率分别为24.2%和56.9%,硬度和强度与淬火速率的对数呈线性关系。随着淬火速率的降低,淬火析出相的尺寸和面积分数显著增大,导致性能下降。淬火速率为1.8℃/s时,淬火析出相的平均尺寸为465.6 nm×158.2 nm,析出相的面积分数为42.1%。     

Responses of the reflectance indices PRI and NDVI to experimental warming and drought in European shrublands along a north-south climatic gradient

The aim of this study was to evaluate the use of ground-based canopy reflectance measurements to detect changes in physiology and structure of vegetation in response to experimental warming and drought treatment at six European shrublands located along a North-South climatic gradient. We measured canopy reflectance, effective green leaf area index (green LAIe) and chlorophyll fluorescence of dominant species. The treatment effects on green LAIe varied among sites. We calculated three reflectance indices: photochemical reflectance index PRI [531 nm; 570 nm], normalized difference vegetation index NDVI₆₈₀ [780 nm; 680 nm] using red spectral region, and NDVI₅₇₀ [780 nm; 570 nm] using the same green spectral region as PRI. All three reflectance indices were significantly related to green LAIe and were able to detect changes in shrubland vegetation among treatments. In general warming treatment increased PRI and drought treatment reduced NDVI values. The significant treatment effect on photochemical efficiency of plants detected with PRI could not be detected by fluorescence measurements. However, we found canopy level measured PRI to be very sensitive to soil reflectance properties especially in vegetation areas with low green LAIe. As both soil reflectance and LAI varied between northern and southern sites it is problematic to draw universal conclusions of climate-derived changes in all vegetation types based merely on PRI measurements. We propose that canopy level PRI measurements can be more useful in areas of dense vegetation and dark soils.     

Plasmonic enhanced fluorescence spectroscopy using side-polished microstructured optical fiber

We report excitation of surface plasmon in a gold-coated side-polished D-shape microstructure optical fiber (MOF). As the leaky evanescent field from the fiber core becomes highly localized by the plasmon wave, its intensity also gets amplified significantly. Here we demonstrate an efficient use of this intensified field as excitation in fluorescence spectroscopy. The so-called plasmonic enhanced fluorescence emission from Rhodamine B has been investigated experimentally. First, plasmonic effect alone was found to provide an immediate fluorescence enhancement factor of two. Second, experimental results show a good agreement with theoretical modeling. Strong evanescent field generation and surface enhancement with simple metallic coating makes this fiber based device a good candidate for compact fluorescence spectroscopy.     

A highly selective triphenylamine-based indolylmethane derivatives as colorimetric and turn-off fluorimetric sensor toward Cu detection by deprotonation of secondary amines

A new triphenylamine-based fluorogenic probe bearing an indolylmethane unit (R1) was developed as a fluorescent chemosensor with high selectivity toward Cu²⁺ over other cations tested. The new probe R1 only sensed Cu²⁺ among heavy and transition metal (HTM) ions in CH₃CN/H₂O (70/30, v/v) solution. The capture of Cu²⁺ by the receptor resulted in deprotonation of the secondary amine conjugated to the triphenylamine, so that the electron-donation ability of the “N” atom would be greatly enhanced; thus sensor showed a 250 nm change in the new absorption band (from 291 nm to 541 nm) and a large colorimetric response, it also exhibited the large decrease in fluorescence intensity at 378 nm and affinity to Cu²⁺ over other cations such as Hg²⁺, Fe³⁺, Pb²⁺, Zn²⁺, Cd²⁺, Ni²⁺, Co²⁺ and Mn²⁺ make this compound a useful chemosensor for Cu²⁺ detection in CH₃CN/H₂O (70/30, v/v) mixture. The probe R1 (c = 1.0 × 10⁻⁶ M) displayed significant fluorescence change and colorimetric change upon addition of Cu²⁺ among the metal ions examined.     

A fluorescent chemosensor for cysteine based on naphthalimide derivative in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize cysteine (Cys) in aqueous solution. The fluorescence enhancement of 1 was attributed to the cyclization reaction of 1 with Cys by 1:1 binding stoichiometry, which has been utilized as the basis of fabrication of the Cys-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Cys indicated that the methods can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Cys-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Cys with a linear range covering from 3.9 × 10⁻⁸ to 1.4 × 10⁻⁵ M and a detection limit of 7.8 × 10⁻⁹ M. And the chemosensor shows excellent selectivity for Cys over other amino acids. Moreover, the response of the chemosensor toward Cys is fast (response time less than 3 min). In addition, the chemosensor has been used for determination of Cys in serum samples with satisfactory results.