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Thermodynamic properties, electronic structures and spectroscopic properties of defects and Ce3+ in Y2O3 are studied by using the hybrid density functional theory associated with multi-reference configuration interaction ab-initio calculations. Thermodynamic transition energy levels of the easily generated oxygen vacancies in the host are analyzed according to HSE06-calculated formation energies, which may be conducive to interpretations of the persistent luminescence (PersL) of Y2O3-based phosphors. Besides, the locations of impurity states (caused by VO and Ce3+) in energy bands are obtained from derived density of states. Moreover, energies and oscillator strengths of 4f1 → 5d1−5 transitions of Ce3+ ions (at Y1 and Y2 sites) calculated from the CASSCF/CASPT2/RASSI−SO method agree reasonably well with experimental excitation spectra of Y2O3: Ce3+ phosphors, achieving the assignment of excitation spectra. The presented calculations can be applied to identify luminescent centers in Ce3+-doped phosphors and reveals possible native defects and their roles in the PersL of phosphors.

In recent years, crystalline-driven self-assembly (CDSA) has received enormous attention, but almost only for block copolymers (BCPs). Herein, we introduced perfluorocarbon chains into main-chain-type liquid crystalline alternating copolymers (ACPs) to obtain perfluoroalkane-containing ACPs with periodic C-I bonds in polymer backbones via step transfer-addition and radical-termination (START) polymerization, followed by an iodine reduction reaction of C-I bonds to induce CDSA of ACPs and put forward a novel concept of "reduction-induced crystallization-driven self-assembly" (RI-CDSA) of main-chain-type ACPs for the first time. Finally, we proposed the folded-chain model and mechanism to explain the novel RI-CDSA behavior, and its rationality has been proved by the corresponding experimental results.

Main-chain liquid crystalline polymers seldom develop into a columnar phase, let alone mesophase transitions between the columnar phase and other phases as the temperature changes. Herein, we present a new series of main-chain liquid crystalline copolymers which consist of strictly alternating rod-like aryl ester core, alkyl chain and perfluoroalkyl segments synthesized by photoinduced step transfer-addition and radical-termination (START) polymerization. The mesophases can be adjusted by changing the length of alkyl chains or perfluoroalkyl segments, which have been fully investigated and simulated in terms of molecular arrangements of molecules. Importantly the resultant liquid crystalline copolymers can present rare reversible phase transitions from a hexagonal columnar phase to a rectangular columnar phase and finally to a smectic phase with temperature increasing.

In this work, we report a much simpler and low-cost method to prepare main-chain-type semifluorinated alternating copolymers by the formation of a halogen bond (XB) complex between α,ω-diiodoperfluoroalkanes and amines/halide salts. It is interesting that the terminal iodine functional group of the polymer chains is easily lost in the amine-promoted system, while the loss can be significantly reduced by adding a small amount of water. Importantly, the system promoted by halide salts can ensure complete retention of the iodine functional group. Overall, the establishment of this method provides a new strategy for designing smart fluoropolymer materials in a green and environmentally friendly facile manner under irradiation with visible light at room temperature.

Side-chain liquid crystalline polymer (SCLCP) usually contains a simple and flexible homopolymer as main chain, while its effect on the self-assembly behavior is often ignored. In this work, in order to increase the structural complexity and investigate the interaction between the main chain and mesogens, perfluorinated segments are introduced into the main chain using a photoinduced Step Transfer-AdditionRadical-Termination polymerization method, producing a novel series of SCLCPs containing 4-methoxyphenyl benzoate mesogens, soft hydrocarbon spacers, and a strictly alternating perfluoroalkyl and alkyl backbone. By adjusting the length of spacers or perfluoroalkyl segments, several mesophases with complex chain packing structures are achieved. This design strategy that constructing highly ordered liquid crystalline (LC) structures from SCLCPs with precise chemical structure provides a facile way toward novel LC nanomaterials.

Introducing fluoroalkyl chains into metallopolymers is a prerequisite to studying the self-organization effect of fluoroalkyl chains and their structure-property relationship. In this work, we present a fluorinated metallopolymer to build an alternating conduction-insulation "molecular fence" model synthesized by the coordination of Ru(II) and a bis-terpyridine-end-capped-phenyl (BTP) ligand modified with fluoroalkyl chains. Taking advantage of scanning tunneling microscopy (STM), a well-aligned periodic linear layered structure is observed clearly, which provides the most direct visualization of the self-organization effect of fluoroalkyl chains for the first time. In addition, combining ultraviolet-visible (UV-vis) absorption spectroscopy and theoretical calculations, we find that fluoroalkyl chains demonstrate a septation effect between two adjacent metallopolymer chains and further restrain the occurrence of interchain charge-transfer transition (ICCT) due to their closed packed structure. This "molecular fence" model can provide a novel route for electron conduction in molecular networks and guide potential applications in the materials science field.

We investigate the influences of W/Ni co-doping on the structural, magnetic, electrical, and optical properties of four-layered Aurivillius Bi5FeTi3O15 ceramics. All the specimens can be indexed with the orthorhombic structure and the space group of A21am. The incorporation of W/Ni significantly promotes the grain’s growth and compactness. Compared with the antiferromagnetic state in pure sample, a weak room-temperature ferromagnetic state is found in the doped samples. The dielectric relaxations in samples with x ≤ 0.1 follow with Vogel–Fulcher relation and can be ascribed to the fluctuation behavior of local polarization, whereas the dielectric relaxation in sample x = 0.15 obeys well Arrhenius law and is due to the localized hopping process of electrons. The piezoelectric measurements indicate that the composition x = 0.05 represents the largest d33 value of 14pC/N at room temperature, which can be attributed to the optimal conductivity. In addition, all the compositions have two absorption edges with the direct inter-band transition due to the electron excitation from the hybridized Bi 6s + O 2p + Fe t2g valence band to Fe eg and Ti 3d conduction bands.

A new photocontrolled iodine-mediated reversible-deactivation radical polymerization (RDRP) strategy to facilely prepare main-chain-type semifluorinated alternating block copolymers was successfully established under irradiation with blue LED light at room temperature, by using a semifluorinated alternating copolymer ((AB)n, where A represents α,ω-diiodoperfluoroalkane and B represents α,ω-unconjugated diene) as a macroinitiator and chain-transfer agent, and methacrylates, acrylates and styrene as the monomers. The end group of (AB)n terminated with perfluoroalkyl iodide –(CF2)n–I can be activated by Ru(bpy)3Cl2/AsAc-Na reducing quenching catalytic cycle which generates initial carbon centered radicals (–(CF2)n˙) to initiate the polymerization under blue LED light irradiation. The polymerization can reach a reversible equilibrium through effective oxygen–iodine halogen bonding in acetone and undergo a photocontrolled iodine-mediated RDRP process. In addition, the “living” features of this photocontrolled iodine-mediated RDRP system were confirmed by polymerization kinetics and controlled “on–off” light switching cycle regulation. What's more, different types of fluoropolymers can be introduced on the copolymer chains due to the powerful designability of (AB)n. Therefore, this strategy can provide a facile and highly efficient approach to the precision synthesis of main-chain-type semifluorinated alternating di/triblock polymers under visible light irradiation.

Stimuli-responsive liquid crystal polymer networks (LCNs) have carved a new path for remote actuation and soft actuators. However, it is still a great challenging work to prepare LCNs with excellent high strength and anti-fatigue properties fitting the transmission model. Herein, for the first time, a prototype of a photocontrolled reciprocating piston “pump” is designed based on near-infrared (NIR) responsive LCNs with alternating fluorine-containing polymer chains. The introduction of fluorinated polymer chains greatly enhances the mechanical strength, extends the durability of the LCNs, and results in the rapid, accurate and lasting NIR-controlled transportation of liquid via the model pump. Amazingly, if the NIR light source is fixed to cycle on for 15 s and off for 20 s automatically, the as-prepared NIR-controlled pump can transport 0.5 mL of liquid each cycle (35 s) and work uninterruptedly for more than 1.0 h without any manually assisted operation.

The structural, magnetic, dielectric and optical properties of Aurivillius Bi6Fe2Ti3O18-based ceramics were investigated in detail. The replacement of Co for Fe/Ti ions obviously varies the grain morphology. Compared with Bi6Fe2Ti3O18 (BFTO) with antiferromagnetic ordering, a spin glass state can be observed in Bi5.25La0.75Fe2Ti3O18 ceramic, while other samples exhibit the ferromagnetic behavior. The specimen Bi6Fe2Ti2(NbCo)0.5O18 (BFTNCO) represents the largest remanent magnetization Mr of 0.93emu/g among all the samples, which can be attributed to the combination of a short lattice parameter c and a large lattice distortion as well as more magnetic ions in a unit cell. The room-temperature dc conductivity of BFTNCO is one order magnitude lower than that of BFTO. In addition, the band gaps of Co-doped samples are about 0.2eV smaller than these of Co-free samples. This work provides a promising path forward to tailor the multiferroic and optical properties in five-layered Aurivillius compounds.

The structural, magnetic, dielectric and magneto-dielectric properties of Aurivillius phase Bi4.25Nd0.75FeTi2(NbCo)0.5O15 (BNFTNCO) ceramics were investigated. X-ray diffraction and Raman results suggest that Nd ions can be effectively incorporated into Bi sites. A typical four-layered Aurivillius structure is confirmed by high resolution transmission electron microscope. The double remanent magnetization 2Mr at 300 K is determined to be 0.88 emu/g, which is one order of magnitude larger than that of Bi5Fe0.5Co0.5Ti3O15 ceramic. The sample undergoes the ferromagnetic and ferroelectric transition at 642 K and 1094 K, respectively. The ferromagnetic Curie temperature is about 200 K higher than that of Bi4.2Nd0.8Fe0.5Co0.5Ti3O15 ceramic. The dielectric relaxation around 300 K with activation energy of 0.435 eV is associate with the hopping process of oxygen vacancies, while the high-temperature dielectric relaxation with a rather large activation energy of Ea= 2.43 eV may be related to the viscous motion of domain walls. More importantly, the intrinsic magneto-electric coupling effect with the magneto-dielectric constant of − 0.57% can be achieved at 300 K and 1 kHz. In addition, the optical band gap Eg of BNFTNCO is 2.50 eV.

The effects of Co ions substitution on the structural, multiferroic, dielectric, and optical properties of Aurivillius Bi5FeTi3O15 are investigated. High resolution transmission electron microscope measurements imply that Bi5FeTi2Nb0.5Co0.5O15 (BFTNCO) exhibits a typical four-layered Aurivillius structure. The co-doping of Nb/Co ions at Ti sites is found to induce the lattice distortion. In comparison with Bi5FeTi3O15 and Bi5Fe0.5Co0.5Ti3O15, the sample BFTNCO shows a more superior multiferroicity with the remanent magnetization Mr and polarization Pr of 76.4 memu/g and 10.2 μC/cm2, respectively. The improved multiferroicity can be ascribed to reduced oxygen vacancy, large lattice distortion and large grain size. In addition, a relatively narrow optical band gap Eg can be obtained as 2.30 eV for BFTNCO. The decreased Eg in BFTNCO can be attributed to large lattice distortion and the overlap of Co 3d state with Ti t2g state. These results reveal that Ti-site doped Aurivillius phase may be the potential candidates for exploring excellent room-temperature multiferroics with narrow band gap.

CT (coiled tubing) acidizing is the main work before horizontal wells put into production in the Middle East. The targeted stimulation interventions directly affect the afterwards performance of production and injection wells. This work not only highlights the importance of removing damage to enhance productivity of producer in the initial production stage, but also put forwards the effective measures of equilibrating flow profiles of injector and producer in the stable production stage. The real-time acidizing techniques combined with distributed temperature sensing (DTS) is used to equilibrate inflow profile in injectors successfully. However, it is lack of effective measures or BHA to guide removing the un-uniform damage and improving acid absorbing in poor interval of horizontal producers. Combined with logging interpretation data and drilling parameters, a velocity-based un-uniform damage model is developed to understand the drilling fluid displacement, mixture and diffusion process in the reservoir-scale. To help ensure accurate acid placement in producer at different production stages, a targeted-acidizing idea is proposed based on the quantitative prediction of inflow and skin factor profiles. To compare the acidizing efficiency between various proposals and illustrate the effectiveness of targeted-acidizing design, A three-dimensional diverted-acidizing simulator is developed for carbonate reservoir, and applied in AHDEB Oilfield, Iraq. According to the simulation of various acidizing designs in new producer, the acid placement based on skin factors can receive the highest productivity compared with traditional uniform, cone-shaped or permeability-based acidizing measures. In the case study, 3 typical acidizing targets cooperated with re-open work of producer have been proposed. The injection rate and acid volume have been optimized through simulation. In order to make under-stimulated intervals absorbing more acid and avoid connecting thief layers, the CT selective acid jetting plus drag back tech is introduced. The production performance after acidizing shows that the stimulation ratio reaches to 7 times. The water cut is also controlled very well. It is difficult to enhance productivity and equilibrate flow profile at the same time under the limited acidizing scale, especially in the long horizontal wells (over 1000m). this paper highlights which goals we should consider firstly at different production stages, and give out the effective measures of evaluation and execution in the matrix acidizing procedure of horizontal wells.

The effects of La ions substitution on the structural, magnetic, ferroelectric and leakage properties of Aurivillius Bi6−xLaxFe1.4Co0.6Ti3O18 (BLFCTO, 0 ≤ x ≤ 1) thin films are investigated. X-ray diffraction (XRD) refinement results indicate that all the samples have an orthorhombic crystal structure and the space group of B2cb. The coexistence of room-temperature ferromagnetism and ferroelectricity can be found in all the samples. Doping La ions can increase ferroelectricity magnitude and decrease leakage current. Furthermore, the energy conversion efficiency can be significantly improved from 16.0 to 53.1% due to the decrease of leakage current. The remanent magnetization 2Mr of 8.2 emu/cm3 and polarization 2Pr of 37.4 µC/cm2 are observed in the x = 0.6 sample. The changes of magnetic, ferroelectric, and leakage properties are discussed in terms of lattice distortion, grain size, oxygen vacancy and compactness. The present work provides an available way to explore room-temperature multiferroics (MFs) and optimize energy efficiency in Aurivillius compounds.

A kind of novel hybrid nanostructure of anodic aluminum oxide (AAO) template or Au sputtered AAO template covered by a single layer NaYF4: Yb3+, Er3+@NaYF4 nanocrystals (NCs) was prepared by a facile strategy. Two kinds of available models that include with and without Au nanolayer were suggested for simulations. Significant downconversion luminescence (DCL) enhancement was observed when the supported template changed from single AAO to Au nanolayer covered AAO. A formula for luminescence enhancement factor based on the cavity quantum optics theory was constructed. With luminescence dynamics analyses, the DCL enhancement was ascribe to the main positive influence of excitation enhancement, besides the minor negative impact of the competition among the nonradiative loss of resonant cavity, the higher order mode loss of Purcell factor, and the increase of radiative transition rate. It proposed a new idea for surface plasmon (SP) induced luminescence regulation mechanism exploration.

The Cretaceous clastic rocks are main targets for petroleum exploration and development in the Abu Gharadig Basin. In this paper, the petrology , lithofacies , and sedimentary environment are studied based on the core samples, thin sections (TS), and scanning electron microscopy (SEM) data of Upper Cretaceous Abu Roash “G” (AR “G”) Member in the AESW Block, Abu Gharadig Basin, Western Desert, Egypt. Petrographic studies suggest that sandstones of the AR “G” are classified as sub-feldspathic arenites, quartz arenites, quartz wackes, and sub-feldspathic wackes. Based on rock textures and fabrics, eight lithofacies are identified within sandstones as gravelly sandstone (Sg), massive sandstone (Sm), cross bedded sandstone (Scb), laminated sandstone (Sl), laminated silty sandstone (Slz), ripple laminated sandstone (Srl), deformed laminated sandstone (Sdl), and bioturbated sandstone (Sb). Siltstone facies are classified as laminated siltstone (Zl), laminated sandy siltstone (Zls), laminated muddy siltstone (Zlm), lenticular siltstone (Zlt), and gravelly siltstone (Zg). Mudstone facies mainly consist of massive mudstone (Mm) and laminated mudstone (Ml). Petrographic study together with Lithofacies, typical sedimentary structures , palynomorphs , and biofacies suggest a tide-dominated coastal environment ranging from subtidal flat to intertidal flat in the study area. The tidal channels and tidal bars in the subtidal flat are the most favorable sedimentary microfacies for AR “G” sandstone reservoirs in the Abu Gharadig Basin, Western Desert, Egypt.

The structural, multiferroic, dielectric, and magneto-dielectric (MD) properties of Aurivillius Bi7Fe2CrTi3O21 ceramic are investigated in detail. The sample shows a dominant antiferromagnetic state with the existence of weak ferromagnetic ordering. The saturation magnetization Ms and remnant polarization Pr are 2.85 emu/g and 4.1 μC/cm2, respectively. The results of dielectric, electrical modulus, impedance and scaling behavior indicate that the dielectric relaxation is induced by the localized hopping process of electrons. In addition, the MD property in low frequency range can be ascribed to the extrinsic effect stemming from grain boundary relaxation, whereas the MD property in high frequency region can be attributed to the intrinsic effect arising from grain relaxation. More importantly, a relatively large intrinsic magneto-dielectric constant of −1.27% can be achieved at 1 MHz and 300 K. These results imply that Cr-doped Aurivillius compounds may be the potential candidates for MD applications.

In this work, Yb3+/Er3+, Ho3+ codoped tetragonal-phase LiYF4 octahedral microparticles have been successfully synthesized through a facile hydrothermal method. Here, we implemented a confocal microscopy setup to manipulate and study the optical properties of a single LiYF4 microparticle under a focused NIR 980 nm excitation. The strong multi-colour upconversion emission intensity with beautiful luminescent patterns have been clearly observed. And output colours (the different ratio of red-to-green emission intensity) of single LiYF4: Yb3+/Er3+, Ho3+ microparticles have been anticipated to be adjusted by controlling Yb3+ doping concentrations. The results show that the different ratio of red-to-green emission intensity of Er3+ and Ho3+ in single LiYF4 microparticle, which is due to the cross-relaxation processes and energy back transfer processes between Yb3+ ions and Er3+ or Ho3+ leading to different population densities of intermediate energy levels. The upconversion emission mechanisms and the influence of Yb3+ concentrations on upconversion emission properties of Er3+ and Ho3+ ions are also discussed according to the emission spectra and rate equations.

A new design of peculiar-shaped β-NaYF4: 20% Yb3+/2% Er3+ hexagonal microcrystal (PSβHM) is proposed and its upconversion (UC) luminescence with adjustable color pattern is studied with near infrared excitation. Flower-like green UC luminescence emission pattern from blooming to withering process and intensive directional red emission are achieved by simply adjusting the focal point position of the excitation light. The mechanism that determines the unique UC luminescence phenomena are investigated systematically. The function of the internal light reflection and waveguide effect with annular microcavity is explored based on the structure characteristic of the hexagonal microplate. The current work may have great significant and potential applications in the development of optoelectronic device, color display, directional light and laser emission of microsystem.

For prediction of the post production of acid fracturing, a numerical method has been introduced in this paper. This prediction approach is developed by the dynamic differential modeling method for forecasting single well acid fracturing performance. In this study, the average production during 30 days and fracture geometry after acid fracturing were determined as predicted indices. Fifteen parameters were considered as influencing factors consisted of geological, reservoir and treatment parameters. The field data of predicted indices and influencing parameters were collected from the data of 7 acid-fractured wells in the XB oil field. The historical data was input into the dynamic differential model to establish and discretize the relation functions. Three target well were chosen and their corresponding influencing factors were used to calculate the predicted indices. The results showed that for the target wells, the modeling predicted indices were fairly close to the real numbers. This model is practical for the engineer in the field since the input parameter acquisition is accessible from the common oil field data. It could help the engineers to optimize the acid fracturing treatment design by correlating the scale of the treatment.

Noble metal nanostructures are currently of great interest for their unique plasmonic property and potential applications in catalysis and surface-enhanced spectroscopy. However, the application of plasmonic nanostructures for quantitatively in situ SERS monitoring of the catalytic reaction has been a great challenge for investigators because combining plasmonics with catalysis requires the same kind of noble metal nanoparticles (NPs) in two very different size regimes. Herein, We have demonstrated a facile wet chemical method to synthesize Au-Ag alloy plasmonic NPs that could combine the desired plasmonic and catalytic properties with same NPs. The catalytic activity of Au-Ag alloy NPs using the reduction of 4-nitrothiophenol (4-NTP) by sodium borohydride (NaBH4) is chosen as a model reaction. The signals of the reaction processes are detected and identified through in situ SERS spectroscopy with high sensitivity. The insights gained by current study may serve as a promising and powerful technique for better investigation in the heterogeneous catalysis. Moreover, the reduction of aromatic nitro compounds with prepared Au-Ag alloy NPs also provides potential application in sewage treatment.

Ag@SiO2/LaF3:Eu3+ core–shell nanostructure was synthesized with a wet chemical method in which the SiO2 layer functioned as a separation layer between Ag-core and LaF3:Eu3+ luminescence material. With this system, surface enhanced luminescene of LaF3:Eu3+ with Ag substrate was investigated, and an obvious enhancement effect was observed. The dependence of the luminescence enhancement on the distance between the luminescence shell and the metallic core was studied too. It is believed that the enhancement effect presented by the current hybrid nanostructure system has great potential in the development of photovoltaic cells.

Due to the high stress difference, high breakdown pressure and undeveloped natural fracture, the pre-acidizing treatment is an effective method for deep shale reservoir hydraulic fracturing. However, the mechanism of complex fracture propagation in the acidized shale is unrevealed. The linear elastic mechanical theory cannot model the elastoplastic deformation of acidized shale and the changes of mechanical properties after acidizing. In this paper, the acidizing damage effect of the shale formation is studied by presenting a numerical model based on the cohesive zone finite element method which is capable for simulating complex fracture propagation. A constitutive model of acidized shale and an equivalent model for simulating the weak planes and natural fractures are embedded into the hydraulic fracturing model. The simulation results of a two-dimensional fracture intersection model considering acid damage effect show that it is more conducive for generation of complex fracture network. A three-dimensional multi-fracture propagation model considering weak planes and acid damage effect is established, and the effects of treatment parameters are analyzed. The simulation results show that the acid-damaged reservoirs are more likely to form complex fractures, which is consistent with the microseismic monitoring results. According to the modeling, the acid treatment could result in a more complex fracture geometry as well as a larger stimulated reservoir volume.

Different amounts of Au nanoparticles decorated NaYF4: Yb3+, Er3+ hexagonal disks were synthesized by using a hydrothermal strategy. In comparsion with single NaYF4: Yb3+, Er3+ hexagonal disk, the average upconversion quenching factors for the green and red upconversion emission bands of single Au nanoparticles decorated hexagonal disk increased obviously with the increasing of the amounts of uploaded Au nanoparticles. The local field distribution accompanied with the enhancement factors were obtained by finite element method. Based on the cavity quantum optics theory, a quantitative analysis for the Au nanoparticles induced quenching was addressed. The results show that the presence of the higher mode Purcell factors induced nonradiative energy transfer from the upconverter to the Au nanoparticles, which contributed to the quenching significantly. The modest weakening of local fields only played a minor role. It could offer a novel theory guidance for the seeking of the novel plasmonic nanostructure-upconverter hybrid system.

Luminescence control and sensitivity increase have attracted widespread attention in luminescence materials and spectroscopy research, which has included investigations on the fundamental mechanisms and potential applications of organic and rare-earth-doped luminescent materials. Along with conventional theory and technique development, surface plasmons and enhanced "hot spots" produced by metal nanostructures provide promising opportunities for luminescence control and intensity enhancement. In the current review, the methods traditionally employed for luminescence control are reviewed, and surface-enhanced luminescence introduced by metal nanostructures is discussed intensively for both organic molecules and rare-earth-doped nanomaterials. It is expected that more systematic and comprehensive exploration on the basic mechanism and techniques can be conducted, and some creative thoughts and methods for efficient luminescence control are suggested.

Hybrid nanostructures composed of rare earth ion-doped lanthanum trifluoride nanocrystals deposited on silica nanospheres (LaF3:Yb3+, Er3+@SiO2) and decorated with varying quantities of silver nanoparticles (Ag NPs) were synthesized using a simple strategy. Down and upconversion luminescence spectra were recorded. The luminescence dynamics were also recorded following excitation with a 532-nm pulse. Silver loading was found to have a significant effect both on the luminescence intensity and the luminescence decay rate, with the samples with the lowest silver content showing reduced luminescence intensity over silver-free samples, while the samples with large levels of silver loading showed significant luminescence enhancement. The results were successfully (and quantitatively) interpreted in terms of the competition between surface plasmon-induced field enhancement mediated by the Ag nanoparticles and nonradiative energy transfer from the luminescent ions to Ag nanoparticles. By combining the measured luminescence intensity with the luminescence decay rate determined from the dynamics measurements, and with the measured surface plasmon absorption spectra, one could obtain a quantitative and self-consistent understanding of the observed dependence of the green 4S3/2→4I15/2 (~540 nm) and red 4F9/2→4I15/2 (~650) emission bands on the Ag NP metal loading.

Tetragonal phase LiYF4:Yb3+/Er3+ microparticles are synthesized via facile hydrothermal method. Single LiYF4 microparticle is excited with IR laser at 980 nm in a confocal setup, and strong green and weak red emissions are observed. It is found that single LiYF4:Yb3+/Er3+ microparticle with sub-structure presents stronger upconversion luminescence emission and smaller intensity ratio of red to green emission than that from LiYF4:Yb3+/Er3+ microparticle with no sub-structure. The possible mechanism, the influence of particle size and the existence of EDTA on the upconversion luminescence emission are investigated. The current study suggests that the luminescence observation with single micropaticle can effectively avoid the influence of environment and neighbor particles, which is important for investigating the luminescence properties of micro- or nano-crystals and for extending their application.

Optical properties of disk-ring plasmonic nanostructures with double symmetry breaking are investigated theoretically. Tunable higher order Fano resonance is achieved, and it is sensitive to the degree of asymmetry of the nanoring, the offset and the dimension of the nanodisk. It is demonstrated that such higher order Fano resonances originate from the destructive interference between the bright mode of the displaced nanodisk and the dark mode of the asymmetric nanoring. By tunning the asymmetry degree of the nanoring, the offset, and the dimension of the nanodisk, certain higher order Fano resonances can be suppressed or enhanced. Double asymmetry breaking also allows the realization of the stronger electric field enhancement, resulting from the stronger interaction between the displaced nanodisk and the asymmetric nanoring.

NaYF4:Yb3+, Er3+, Mn2+ nanocrystals with cubic crystal phase were obtained by a facile solvothermal method through doping a proper amount of Mn2+ ions to the nanocrystals. The results of XRD and TEM showed that the as-prepared samples were well crystallized and their average size was about 25 nm. Under excitations at 978.5 nm and at 532 nm, obvious enhancement and regulation of upconversion and downconversion fluorescence were obtained. Upconversion emission spectra indicate that these effects were independent of doped concentrations of Er3+ and Yb3+, excitation power, and the excitation wavelength in the current study. It is concluded that the enhancement of fluorescence emissions is mainly due to the change of local symmetry around Er3+ ions, while the regulation of red-to-green ratios was caused by efficient energy transfer between Er3+ and Mn2+ ions. This kind of upconversion material has a great potential in bioimaging and drug delivery since the excitation and emission falls into the region of "optical window" of biological tissues.

Pr3+/Yb3+ co-doped hexagonal NaYF4(beta-NaYF4) microprisms were synthesized by the hydrothermal method, and ethylenediaminetetraacetic acid (EDTA) was introduced to control the size of the microcrystal samples. Bright upconverted fluorescence emission was observed when the samples were excited with an infrared (IR) laser at 976.4 nm. The emission was found to originate from the transitions of 3P0-3F2, 3P0-3H6 or 1G4-3H4, 3P1-3H6, 3P0-3H5, 3P1-3H5, and 3P0-3H4 of Pr3+ ions. Possible mechanisms for upconversion fluorescence and concentration dependence as well as the crystal structure and its formation of NaYF4:Yb3+/Pr3+ microprisms were explored and discussed based on the experimental observations.

Rare earth ion-doped upconversion materials show great potential applications in optical and optoelectronic devices due to their novel optical properties. In this work, the NaYF4:Yb3+/Ho3+ microrods have been successfully prepared by a hydrothermal method assisted with EDTA (ethylenediaminetetraacetic acid). Time controlled experiments were carried out and the growth mechanism of dissolution–recrystallization of the microrods is proposed. It is important that the unusual upconversion emission with a candy-like pattern from single NaYF4:Yb3+/Ho3+ microrods can be detected by confocal microscopy under NIR 980 nm excitation. The influence of the particle number on the UC emission spectra and the overall luminescence color was investigated systematically. We noted that the multicolor emission from the single NaYF4:Yb3+/Ho3+ microrods can be successfully obtained only by adjusting the excitation strength or the size of the microrods. The present study is of great importance for multicolor tuning of RE-doped NaYF4 nano/micromaterials as well as for understanding the up-mechanism. In addition, the luminescence from single microparticles can provide more precise spectral information on three-dimensional displays and biological labels.

In this work, hexagonal phase NaY(Gd0.4)F4:Yb3+/Ho3+ nanocrystals were obtained by solvothermal method. The upconversion emission tuning from green to red in NaY(Gd0.4)F4:Yb3+/Ho3+ nanocrystals was successfully achieved by replacing Y3+ ions in the nanocrystal structure with Ce3+ ions under 980 nm excitation. The red upconversion emission intensity was enhanced with Ce3+ concentration increasing. The output colors for the samples can be clearly observed in a confocal microscopy setup. It was found that two efficient cross-relaxation processes between Ho3+ and Ce3+ ions had been employed to enhance red emission and suppress green emission. The possible upconversion mechanisms and conversion efficiency between Ho3+ and Ce3+ ions were investigated in detail. In addition, the influence of the matrix and surface properties on the upconversion emission of the samples was also discussed. The red upconversion emission of Yb3+, Ho3+ and Gd3+ codoped nanocrystals in this work will have great potential applications in biological imaging, magnetic resonance imaging agents, and display and anti-counterfeiting applications.

The first-principles calculations in the combination of hybrid density functional theory (DFT) and multiconfigurational quantum-chemical methods are carried out to investigate geometric structures, electronic structures and 4f → 5d transitions of Ce3+ ions at mixed Ca2+/Y3+ sites in the CaYAlO4 (CYAO). The most energetically stable unit cell among three nonequivalent configurations is firstly determined according to the total energies from DFT calculations. The calculated defect formation energies of lanthanide dopants and complexes in the host (with relatively stable configurations) then reveal the preferred substitution of Ce3+ ions in the host. Moreover, the energies and relative oscillator strengths of the 4f → 5d transitions of Ce3+ at both Ca2+ and Y3+ sites are derived from the embedded-cluster quantum-chemical calculations at the CASSCF/CASPT2/RASSI−SO level. By comparison, the excitation bands in the experimental spectra of Ce3+-doped CYAO phosphors are mainly attributed to 4f → 5d transitions of Ce3+ ions at Ca2+ sites, which is well consistent with the conclusions attained from the calculations on defect formation energies. The computational framework presented in this study is beneficial to identify the occupation sites of lanthanide ions and assign the excitation bands of the experimental spectra for the phosphors with mixed sites or solid-solution structures.

Uniform hexagonal β-NaLn1F 4 :Yb 3+ , Ln2 3+ (Ln1 = Y, Lu; Ln2 = Er, Ho, Tm, Eu) disks were synthesized with hydrothermal method in which the sodium citrate was used as a shape modifier. The experimental observation indicated that both upconversion and downconversion fluorescence emissions were significantly stronger in β-NaLuF 4 than that for β-NaYF 4 . It was found that the stronger hypersensitive transitions were mainly due to the increase of J–O parameter ( Ω 2 ) in β-NaLuF 4 host, while the stronger insensitive transitions were mainly caused by the stronger overlap of electron cloud that was induced by the decrease of Ln F bond lengths. Additionally, the larger absorption strength in the near-infrared region is another important factor for the stronger fluorescence emissions. The current research has a great potential in improving near-infrared conversion efficiency of silicon solar cells.

Fluoride nanoparticles of Ln3+ (Ln3+=Pr3+, Nd3+, Sm3+, Gd3+,Tb3+ Dy3+, Ho3+, Er3+, Tm3+, Yb3+)/Eu3+:LaOF and Eu3+:LaOF with rhombohedral crystal structure were prepared by a hydrothermal-sintering method. The red fluorescence emission of Eu3+ ions was found to be enhanced with most of the co-dopant Ln3+ ions. Compared with strong fluorescence emission at 610 nm of Eu3+:LaOF nanoparticles, the enhancement factors was up to ten times in Ln3+ (Ln3+=Gd3+, Dy3+, Tm3+)/Eu3+:LaOF co-doped nanoparticles. The results show that the asymmetry of the local environment of Eu3+ ion was reduced by co-doping Ln3+ ion into the nanoparticles, and that energy transfer might occur between Eu3+ and codopant Ln3+ ions, which is suggested as the source of the observed fluorescence enhancement.

A series of β-NaYF 4 microrods doped with Yb 3+ /Er 3+ have been successfully synthesized through a facile hydrothermal method. The fluoride microcrystals have been characterized by XRD, SEM, and the photoluminescence spectra method. The upconversion spectra show that the output light color have been tuned from green to red under near infrared excitation at 977 nm when replacing Y 3+ ions with a different amount of Yb 3+ in NaYF 4 :Yb/Er microcrystals. The effect of the intrinsic structural feature of fluoride compounds and four external factors, namely the concentration of Yb 3+ , the concentration of Er 3+ , the particle size and the use of an organic additive (EDTA), on the ultimate output light color of samples are investigated detailedly. The results show that the output light color is more sensitive to the concentration of Yb 3+ than that of Er 3+ . When elevated the concentration of dopants (Er 3+ or Yb 3+ ) in the NaYF 4 host lattice, the cross-relaxation process derived from Er 3+ promoted the red emission and quenched the green emission.

Efficient up and down frequency conversions in Tm(3+) and Ho(3+) doped LaOF tetragonal nanocrystals have been investigated. Bright fluorescence emissions are obtained in co-doped Tm(3+)/Ho(3+):LaOF tetragonal nanocrystals through UV and infrared excitation. Green florescence from doped Ho(3+) ions, which can be clearly seen with bared eyes, is obtained when Tm(3+) ion is excited. Specific mechanism of the cross relaxation between doped ions is explored through spectroscopic measurements in time and frequency domains. About 90% energy transfer efficiency is obtained when the weak radiative and nonradiative relaxations are neglected.

Optical transitions of Eu(3+)-doped LaOF nanocrystals with tetragonal and rhombohedral structures were studied experimentally using laser spectroscopic method. Fluorescence emissions from 5D1 and 5D0 of Eu3+ in LaOF nanocrystals were detected by exciting the sample with a 532 nm pulsed laser, and the influence of local symmetry on the fluorescence emission of doped ions was observed. The specific crystalline phase as well as the local symmetry on the fluorescence emission was investigated in both the frequency domain and time domain. It was found that Eu3+ ions doped in the tetragonal crystal structure present more efficient fluorescence emission, which was explained by lower symmetric distribution of local field at the doped ions.

Pr3+/Yb3+ co-doped hexagonal NaYF4(beta-NaYF4) microprisms were synthesized by the hydrothermal method, and ethylenediaminetetraacetic acid (EDTA) was introduced to control the size of the microcrystal samples. Bright upconverted fluorescence emission was observed when the samples were excited with an infrared (IR) laser at 976.4 nm. The emission was found to originate from the transitions of 3P0-3F2, 3P0-3H6 or 1G4-3H4, 3P1-3H6, 3P0-3H5, 3P1-3H5, and 3P0-3H4 of Pr3+ ions. Possible mechanisms for upconversion fluorescence and concentration dependence as well as the crystal structure and its formation of NaYF4:Yb3+/Pr3+ microprisms were explored and discussed based on the experimental observations.

The tetragonal LaOF:Eu3+ nanoparticles have been successfully synthesized by three different methods including hydrothermal, solvothermal and chemical precipitation methods. Strong red fluorescence emissions were observed by exciting the samples with 532 nm laser. Under the proper conditions, the sample synthesized via chemical precipitation method presented the strongest fluorescence emission. It is found that the particle size, surface modification, crystal structure and local environment could be adjusted with different preparation processes.

Nano-scaled and micro-scaled Tm(3+)-doped LaF3 were prepared by a hydrothermal technique. Two-photon resonant excitation from the ground state 3H6 to the excited state 1D2 was fulfilled by two pulsed dye lasers tuned at 656 nm and 643 nm, respectively, which were resonant with the ground state absorption of 3H6 --> 3F2 and the excited state absorption of 3H4 --> 1D2. The time evolution of the corresponding state was investigated with blue upconverted emission by tuning the delay of two excitation lights. The results showed that the nonradiative relaxation of the 3F2 state was mainly affected by the confinement effect, while the radiative relaxation of 3H4 state was significantly influenced by the Tm3+ concentration.

Tm(3+):LaF(3) nanocrystals were synthesized with hydrothermal technique. Local-field effect on the radiative relaxation rate was studied in the system of Tm(3+):LaF(3) nanocrystals immersed in several liquid media. The fluorescence lifetime was measured. It was found that the fluorescence decay presented the characteristics of second-order exponential decay, for which the contribution from the ions inside the nanocrystal and ions at the interface of the nanocrystal were distinguished. Investigating the experimental results with proposed models, we found that the surface effect had to be eliminated. For rare earth doped LaF(3) nanocrystals, real-cavity model well explains the influence of surrounding medium on the fluorescence relaxation rate.

A novel hybrid nanostructure, that is a Ag nanoparticle decorated LaF(3):Yb(3+)/Ln(3+)@SiO(2) nanosphere (Ln=Er, Tm), was constructed by a facile strategy, and characterized by XRD, TEM, FTIR, XPS and UV-vis-NIR absorption. Obvious spectral broadening and red-shift on the surface plasmon resonance were obtained by adjusting the size and configuration of Ag nanoparticles. Effective upconversion luminescence enhancements for Er(3+) and Tm(3+) containing samples were obtained. It is suggested that the luminescence enhancement results from both the excitation and emission processes, and the configuration of the studied hybrid nanostructure is an efficient system to enhance the luminescence emission of rare earth doped nanomaterials. It is believed that the enhancement from the hybrid nanostructure will find great potential in the development of photovoltaic solar cells.