The LSPR regulation of TiO2: W nanocrystals and its application in enhanced upconversion luminescence

The localized surface plasmon resonance (LSPR) absorption peaks of semiconductor nanocrystals are mainly concentrated in the infrared band, and the absorption characteristics can be controlled by the amount of element doping. The coupling of upconversion nanocrystals (UCNPs) and semiconductor nanocrystals can improve the upconversion luminescence (UCL) of rare-earth ions. Here, the LSPR absorption and morphology of the semiconductor nanocrystalline TiO₂: W were adjusted by using ammonium fluoride during synthesis. Significant absorption enhancement of TiO₂: W in the near-infrared region was obtained to enhance the UCL of NaYF₄: Yb³⁺, Er³⁺. The Glass/NaYF₄: Yb³⁺, Er³⁺/TiO₂: W@SiO₂ layered structure films were fabricated through spin coating. Compared with Glass/NaYF₄: Yb³⁺, Er³⁺, the green and red lights of the Glass/NaYF₄: Yb³⁺, Er³⁺/TiO₂: W@SiO₂ films were enhanced by 15.9 and 17.8 times, respectively. The UCL enhancement of Glass/NaYF₄: Yb³⁺, Er³⁺/TiO₂: W@SiO₂ was derived from the LSPR property of TiO₂: W through the enhancement of the excitation. The present work is important for possible applications of these layered structures as biomarkers, photocatalysts, flexible materials, and photoluminescence display panels.     

Plasmon enhanced upconversion luminescence of NaYF(4):Yb,Er@SiO(2)@Ag core-shell nanocomposites for cell imaging

NaYF(4):Yb,Er@SiO(2)@Ag core-shell nanocomposites were prepared to investigate metal-enhanced upconversion luminescence. Two sizes (15 and 30 nm) of Ag nanoparticles were used. The emission intensity of the upconversion nanocrystals was found to be strongly modulated by the presence of Ag nanoparticles (NPs) on the outer shell layer of the nanocomposites. The extent of modulation depended on the separation distance between Ag NPs and upconversion nanocrystals. The optimum upconversion luminescence enhancement was observed at a separation distance of 10 nm for Ag NPs with two different sizes (15 and 30 nm). A maximum upconversion luminescence enhancement of 14.4-fold was observed when 15 nm Ag nanoparticles were used and 10.8-fold was observed when 30 nm Ag NPs were used. The separation distance dependent emission intensity is ascribed to the competition between energy transfer and enhanced radiative decay rates. The biocompatibility of the nanocomposites was significantly improved by surface modification with DNA. The biological imaging capabilities of these nanocomposites were demonstrated using B16F0 cells.     

Enhancing upconversion luminescence and thermal sensing properties of Er/Yb co-doped oxysulfide core-shell nanocrystals

The development of noncontact thermal probe based on stable inorganic materials of trivalent lanthanide (Ln³⁺) doped phosphors with nontoxicity is of vital importance for their promising applications in bio-medical fields. Here we explore the upconversion luminescence and thermal sensing properties of Er³⁺, Yb³⁺ co-doped oxysulfide in a broad temperature range of 300-583 K. It was found that constructing an active shell with an optimum concentration of sensitizers is an efficient way to improve both the luminescent intensities and thermal sensitivity. Compared with the core-only sample, the luminescent intensity of the Y₂O₂S: Er³⁺, Yb³⁺@ Y₂O₂S: 5%Yb³⁺ sample is significantly enhanced by 12-fold at excitation of 980 nm. While further increasing the Yb³⁺ concentration in the shell activates new quenching pathways of Er³⁺ → Yb³⁺ → quencher from the core to the shell. Similar quenching mechanisms are also observed at excitation of 1550 nm. These energy transfer processes and luminescence mechanisms are verified in the fluorescence decay measurements. Furthermore, coating the core sample with an active shell doped by 10% Yb³⁺ enhances the thermal sensitivity by 30%, holding a high and stable sensitivity more than 50 × 10⁻⁴ K⁻¹ in a broad temperature range of 423-573 K at 980 nm excitation. In addition, at the much safer excitation wavelength of 1550 nm, this sample achieved the maximum sensitivity of 45 × 10⁻⁴ K⁻¹ at 503 K. Our work contributes a feasible and versatile way to promote the luminescence and thermal sensing properties of Ln³⁺-based materials, combining with the nontoxic oxysulfide host, indicating their potential applications as safe fluorescent and temperature nano-probes in bio-field.     

基于上转换发光的可见/近红外光催化研究现状及展望

上转换发光材料可将低能光子转换为高能光子,对于太阳能的转化利用具有潜在的应用前景。本文以TiO₂为例,介绍了上转换发光在可见/近红外光催化领域的研究背景,说明了光能吸收、光能转换、光能转移、表面反应的光能利用机制,总结了上转换发光的研究进展。同时重点分析了稀土上转换发光在可见/近红外光催化领域的研究现状,阐述了上转换发光与其它改性方法协同提高TiO₂光催化效率的基本原理。最后提出了基于复合上转换发光的光催化研究思路,展望了上转换发光在光催化中的应用前景。     

Fabrication and upconversion luminescence properties of Er:SrF2 transparent ceramics compared with Er:CaF2

SrF₂ transparent ceramic is a promising upconversion material due to the low phonon energy. The effect of different sintering temperatures on Er:SrF₂ transparent ceramics was investigated. The suitable sintering temperature for Er:SrF₂ transparent ceramics was 900 °C by hot-pressed sintering in this study. High quality of Er:SrF₂ transparent ceramics with different doping concentrations were obtained. The upconversion luminescence spectra and decay behavior were compared between Er:SrF₂ and Er:CaF₂ transparent ceramics with different Er³⁺ doping concentration. The green emission of 5 at.% Er:SrF₂ ceramic was much stronger than that of 5 at.% Er:CaF₂ ceramic, while the red emission of Er:SrF₂ ceramic was almost the same as that of Er:CaF₂ ceramic. The upconversion luminescence lifetime of Er:SrF₂ transparent ceramics was longer than that of Er:CaF₂.All the results indicated Er:SrF₂ transparent ceramics was a candidate for green fluorescent upconversion materials.     

Investigation of high-level waste glass melting using X-ray computed tomography

A method has been developed to quantitatively assess the melting behavior of simulated nuclear waste glasses in a 5-cm-diameter stainless steel beaker heated from the bottom. The method applies X-ray scanning and computed tomography to build three-dimensional volumetric data of a heat-treated sample and performs an adaptive segmentation analysis of the volumetric data to identify morphologically distinct regions in the sample matrix and quantify the amount of material in each region based on computed tomography density. The method was applied to two different series of simulated high-level waste glass melter feeds, and the results showed that it provides detailed images of samples at various stages of melting, including distribution of gas bubbles of varying sizes within the sample matrix, as well as a quantitative measure of how fast various waste/frit feeds melted relative to each other. The results show that the melting rate is influenced by the rate of calcine gas evolution, melt viscosity, and the presence of modifier ions in the feed.     

Effective regulation of upconversion luminescence in NaErF4 and NaErF4@SiO2 core-shell particles

Upconversion luminescence materials have gained extensive attentions owing to their unique luminescence characteristics of converting near-infrared excitation to visible light emission. However, how to improve the doping concentration of activator (usually <3 mol%) in traditional sensitizer-activator system is still a great challenge due to the luminescence quenching effect. In this work, NaErF₄ crystals with diverse crystal phases and morphologies were prepared by simple hydrothermal method, constructing a 100% doping concentration system of activator (Er³⁺). With the increase of F^? content, the phase of NaErF₄ transfers from cubic to hexagonal, and the morphology changes from nanospheres to hexagonal microflakes, meanwhile, the upconversion luminescence intensity also increases gradually. In addition, in order to further inhibit the luminescence quenching effect of NaErF₄ bare core, a series of NaErF₄@SiO₂ core-shell samples with different SiO₂ shell thickness were successfully prepared. Compared with NaErF₄ bare core, the morphology and structure of the NaErF₄@SiO₂ core-shell samples have no obvious change, but the UC luminescence intensity is significantly enhanced. Interestingly, the change of NaErF₄ crystal phase and SiO₂ shell thickness can both bring about multicolor luminescence. In addition, different from the traditional NaYF₄:Yb, Er co-doping system, the as-prepared hydrophilic NaErF₄ and NaErF₄@SiO₂ samples showed a greater red to green ratio (R/G > 1), which may expand their potential applications in biological imaging and sensing fields.     

Bi3+ as an enhancer for down- and upconversion luminescence in ternary vanadate structures

A series of dual-mode nanomaterials based on Ba₂LaV₃O₁₁:Yb³⁺, Er³⁺, Bi³⁺, with different bismuth content were synthesized using the hydrothermal method. Various analytical methods, such as x-ray diffraction (XRD) with additional detailed Rietveld analysis, transmission electron microscopy (TEM), inductively coupled plasma mass spectroscopy (ICP-MS) and laser spectroscopy have confirmed that with increasing Bi³⁺ content, phase purity, optical absorption and luminescence intensity significantly increased. Moreover, a slight luminescence color tunability was observed along with the gradual introduction of bismuth into the host structure since, among the others, the local crystal field around emitting Er³⁺ ions was changing. The use of ultraviolet and near-infrared excitation wavelengths allowed to obtain a dual mode luminescence, which extended the emission range and demonstrated the possibility of using the studied materials, e.g. in solar cells.     

Functionalizable composite nanoparticles as a dual magnetic resonance imaging/computed tomography contrast agent for medical imaging

A dual contrast agent for computed tomography (CT) and magnetic resonance imaging (MRI) was synthesized via microemulsion polymerization. This contrast agent consists of Fe₃O₄ particles (d = 7 nm) with an iodine-carrying nanopolymeric shell, with overall particle sizes ranging from 50 to 250 nm. 2-Methacryloyloxyethyl(2,3,5-triiodobenzoate) was used as the monomer. Sodium oleate was used as the surfactant and its amount was varied to control the overall particle size. The composite nanoparticles were mainly characterized via dynamic light scattering, with further analyses using transmission electron microscopy and atomic force microscopy. The particles provided a highly visible contrast in CT and MR images. A template for biomedical applications was created by adding a comonomer and the particles were further functionalized with the somatostatin analogue Tyr³-octreotate. The particles were tested for specific uptake into somatostatin receptor-positive AR42J cells. The additional uptake of the functionalized particles was investigated. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47571.     

Er3+ concentration-dependent microstructural and upconversion luminescence process of transparent perfluoride composite glass

Er³⁺-doped transparent perfluoride composite glass (PFCG) containing SrF₂ crystals was obtained by a one-step method. PFCG was observed to maintain the formation of a single SrF₂ crystal phase even when the Er³⁺ doping concentration was as high as 8 mol%. Importantly, Er³⁺ was enriched in the crystalline region, which promoted grain growth. This ensures effective emission of upconversion (UC). Interestingly, green and red UC emissions were found to be tunable in the range of 1–6 mol% Er³⁺ doping, and the UC emission and lifetime started to produce concentration quenching until 6 mol% Er³⁺ doping. To the best of our knowledge, this is the highest quenching concentration of Er³⁺ in composite-glass materials. Moreover, the dominant UC process was systematically analyzed at different doping levels. This research is expected to provide ideal candidate materials and appropriate Er³⁺ concentration doping level guidance in PFCG for the field of UC lasers.     

Local displacement measurements within adhesives using particle tracking and In Situ computed tomography

Strain measurements are essential for understanding the mechanical behavior of bonded joints under different load conditions and for validating numeric simulations. Strain gauges and extensometers are typically used to determine local strains in a specific direction. The introduction of digital image correlation (DIC) allows for the full-field measurement of surface strains both in two dimension and in three dimension. However, these methods observe the strain of the adhesives’ surface which may vary in comparison to the volumetric strains.In this article, a new technique for measuring the internal displacement field in adhesives is proposed. The method is based on in situ x-ray computed tomography (CT) and particle tracking. Basic approach of the measurement is to identify and track characteristic markers within adhesives during loading. The displacement due to the load can be calculated by the different positions of the characteristic markers between two image sets. Initial results for a single lap joint with a thick bond line indicate that a sufficient resolution of the measurement can be reached and motivate further research to develop this novel measurement technique for adhesives.     

基于XCT的气固流化床布风板射流特征研究

构建了X光层析成像（XCT）气固流动参数测量系统,基于锥形束滤波反投影算法（FDK）开发了CT三维重建软件,并设计了射流识别及量化算法。基于以上方法获得了不同流化风速下床料粒径d_p、布风板孔口直径d₀和布风板孔口均分面积A₀对射流形态结构和几何特征的影响规律。结果表明平均射流长度L、最大直径D和体积V与床料粒径d_p成反比,与孔口直径d₀和孔口均分面积A₀成正比,最终拟合了流化床平均射流长度关联式。     

Measurement of particle concentration in powder coating process using capacitance computed tomography and wavelet analysis

Capacitance computed tomography techniques were used to visualize particles movement in the draft tube of a spouted fluidized bed for the coating process of drug production. A total of 512 frames images of the particle concentration distribution were obtained at 10-millisecond intervals over a coating time of 5 min using a capacitance computed tomography system. The three-dimensional capacitance CT images (time and two-dimensional space images) were decomposed to wavelet time and space levels to extract the dominant particle distribution feature using three-dimensional discrete wavelet multiresolution at different coating times. As a result, the time and space dominant particle distribution with a specific frequency level can be visualized.     

Anisotropic thermal diffusivity and conductivity in SiC/SiC tubes studied by infrared imaging and X-ray computed tomography

Traditional flash diffusivity evaluation of thermal diffusivity/conductivity of composite tubes require machining of specimens. For a thin-wall tube, this method can only be used to obtain through-thickness transport property. A novel method to evaluate anisotropic thermal diffusivity in a composite tube has been developed. Braided SiC/SiC composite tubes were subjected to a xenon flash heating pulse. A high-speed, high-sensitivity infrared camera was used to measure surface temperature changes as a function of time and nondestructively detect subsurface defects/damages, such as macroscopic pores. Standard reference material (Pyroceram 9606) and curved SiC/SiC composite tube specimens were used to validate thermal diffusivity obtained from infrared imaging. Unlike the traditional method, there is no need prepare special specimens, and thermal diffusivity values in three orientations are obtained after a single flash. A finite element analysis model based on x-ray computed tomography scans was developed to simulate the heat transfer. This technique is significant in assessing thermal conductivity and inspecting the health of ceramic tubes during and after service.     

Evaluation of the morphology and pore characteristics of silica refractory using X-ray computed tomography

Silica refractory has excellent high-temperature performance, but its apparent porosity is relatively high. In this work, samples obtained before and after creep testing of silica brick (1550 °C, 50 h), from used silica checker brick (existing only tridymite and amorphous) and from used dome brick (existing only cristobalite and amorphous) were investigated using a three-dimensional structure model based on X-ray computed tomography (CT). The results show that the porosity of silica brick was high but consisted mainly of interconnected pores, with a very small proportion of closed pores (smaller after long-term use). During the use of silica brick, the morphology and phase transformation caused large particles to rupture, and the mineralizer became liquid at high temperature. The broken particles and interconnected pores provided channels for the migration of the liquid in the brick at high temperature. The silica brick presented a homogeneous ceramic structure during long-term operation. Tridymite or cristobalite presented a solid frame leading to an excellent creep performance of the silica brick (the creep rate of the checker brick was ?0.16% at 1550 °C for 50 h). Results were discussed, compared with literature and a model for the transformation of the silica brick from a refractory structure to a homogeneous ceramic structure was established in this paper.     

Designing and temperature sensing characteristics of upconversion luminescence core-shell structures with negative and positive thermal expansion

Generally, lanthanum ions doped positive expansion and negative expansion materials exhibit thermal quenching and enhancement of upconversion luminescence (UCL), respectively. Combining the UCL characteristics of positive expansion and negative expansion lattices is of importance for developing efficient temperature sensing systems. Here, positive expansion TiO₂:Yb³⁺, Er³⁺ three dimensionally ordered macroporous film was prepared by the template-assisted approach, and the Yb₂W₃O₁₂: Er³⁺ solution was filled into the TiO₂: Yb³⁺, Er³⁺ three dimensionally ordered macroporous film. After secondary sintering, the shell of negative expansion Yb₂W₃O₁₂: Er³⁺was formed on the surface of TiO₂:Yb³⁺/Er³⁺ core. Under 980 nm excitation, the red and green UCL is predominate for the spectra of TiO₂:Yb³⁺/Er³⁺ core and Yb₂W₃O₁₂: Er³⁺ shell, respectively. With the measurement temperature increasing, the green UCL from negative expansion Yb₂W₃O₁₂: Er³⁺ shell increases, while the red UCL from positive expansion TiO₂:Yb³⁺, Er³⁺ core decreases. The performance of temperature sensing was characterized by the monitoring the UCL intensity ratio between 525 nm and 660 nm. The temperature sensitivity is about 1.12% K^?1, which is larger than that of thermally coupled FIR technology. We believed that the present work is instructive for developing new generation temperature sensor.     

X-ray computed tomography in large bubble columns

X-ray computed tomography (CT) is used to explore the differences in a semi-batch bubble column operated at superficial gas velocities of U_g=3, 10, and 18 cm/s. Air-water or air-water-cellulose fiber systems comprise the multiphase flow, and the bubble column has a 32.1 cm internal diameter. A CT image of a phantom object composed of several air-filled tubes immersed in water is used to identify several characteristic features of the X-ray CT system. CT images are then compared between air-water and air-water-cellulose fiber systems. When the fiber mass fraction is 0.1%, gas holdup is slightly higher than that of the air-water system in the column center and near the column wall. In 1.0% cellulose fiber slurries, gas holdup is lower than that of air-water results at all radial positions.     

Phase transitions and upconversion luminescence in oxyfluoride glass ceramics containing Ba4Gd3F17 nanocrystals

Novel transparent Er³⁺ doped oxyfluoride glass-ceramics containing Ba₄Gd₃F₁₇ nanocrystals were prepared by melt quenching followed by heat treatment of as-prepared glasses. The phase composition and microstructure were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Intense upconversion luminescence (UCL) was detected. Longer characteristic decay times and splitting of the luminescence bands compared to the precursor glass indicated the incorporation of erbium ions in the crystalline phase. The spectroscopic properties of glass ceramics were compared with single phase cubic and rhombohedral Ba₄Gd₃F₁₇ ceramics. The unit cell parameters and atomic positions in the rhombohedral phase were calculated using Rietveld refinement. The local environment of Er³⁺ and the phonon energy of both polymorphs were analyzed using luminescence and Raman spectroscopy. In the glass ceramics, a phase transition from distorted metastable fluorite to ordered rhombohedral Ba₄Gd₃F₁₇ was observed and resulted in the enhancement of the efficiency of UCL.     

The investigation of gas holdup distribution in a two-phase bubble column using ultrasonic computed tomography

In this study, time-averaged gas holdup distributions were investigated in a 16 cm diameter bubble column for two-phase dispersed system of air–water and air–glycerol solution of 10 wt% by using ultrasonic computed tomography (UCT). A quantitative result of UCT – as a coupling of the ultrasonic transmission method and the iterative filtered backprojection (IFBP) image reconstruction technique – is presented. The UCT results are in a good agreement with those by the bed expansion method. A higher gas holdup in the air–glycerol 10 wt% solution than in the air–water system was observed. The distribution of gas holdup in the column with an attached baffle is also investigated by UCT.     

Analysis of distributions of gas and TiO2 particles in slurry bubble column using ultrasonic computed tomography

The ultrasonic computed tomography (UCT) as a coupling of the ultrasonic transmission method and the image reconstruction technique based on the iterative filtered back-projection was applied to investigate the cross-sectional distributions of gas and particle holdups in a slurry bubble column. The dispersion system of air–water–TiO₂ was used in this study. The loading of the titanium dioxide particle has affected on the increase of the gas holdup. The UCT was used to analyze the macroscopic flow scheme of the system under various operating conditions. Based on the experimental results and the observation during the experiments, the macroscopic bubble flow scheme may be considered to be a helical rising flow.