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Herein, Lu3Mg2GaSi2O12: Ce3+/Sm3+ (LMGS) phosphors with a garnet structure were synthesized by a high-temperature solid-phase reaction method, and their potential application in w-LEDs was evaluated. In this study, the crystal structure of the phosphor was determined using the Rietveld method and XRD pattern analysis, while the luminescence performance was characterized by the relevant PL spectrum, and then, the energy transfer (ET) mechanism was explored. When subjected to an excitation at a wavelength of 450 nm, the introduction of Sm3+ ions into LMGS: 0.015Ce3+ broadens the broadband emission of Ce3+ ions owing to the co-excitation and ET of Ce3+ and Sm3+. A continuous and controlled variation in the Sm3+ doping concentration facilitates the tuning of color coordinate from green to yellow. The maximum Ce3+→Sm3+ energy transfer efficiency of the sample was 55.64 %. From the viewpoint of practical applications, the sample exhibited excellent thermal stability and water resistance. After combining the LMGS: 0.015Ce3+, 0.03Sm3+ sample with a commercial red phosphor and a blue chip, a warm white LED with a color rendering index of 86.6 and color temperature of 3592 K can be obtained.

Ce3+-doped Lu3Mg2GaSi2O12 (LMGS) yellow-green phosphors were synthesized by a high-temperature solid-state reaction method for 3 h. The optical properties and crystal structure of the obtained samples were characterized by spectral analysis and Rietveld refinement, respectively. The emission spectra excited by 460 nm exhibit broad yellow-green emission bands from 525 to 535 nm (having short redshift with increasing Ce3+ concentration). At 423 K, the emission intensity of the LMGS: 0.0015Ce3+ phosphor decreases to 81.94% of that at room temperature, and the activation energy is approximately 0.153 eV. The samples presented good water resistance. Finally, we packaged the obtained green phosphors and commercial red phosphors Sr2Si5N8: Eu2+ with a blue LED chip. The color-rendering index and correlated color temperature of the packaged w-LED under 460 nm excitation were 84.2 and 4034, respectively. All the above results indicate that the LMGS: Ce3+ samples have great potential for applications in w-LEDs.

In this work, multi-component fluoride phosphors BaxNay−nMnYzF2x+y+3z+3m : Er3+m (M = Li and K) sensitive to 1550 nm were synthesized by the low-temperature combustion synthesis (LCS) method. The optimum batch formula was determined by orthogonal experiments. The effects of introducing alkali ions (Li+, K+) on phase formation and luminescence intensity were systematically studied. The results indicate that the luminescence intensity of 0.2 mol% Li+-introduced nanoparticles is obviously enhanced, and the diffraction peak is shifted to the direction of a smaller diffraction angle, which is attributed to the lattice expansion caused by Li+ ions entering the lattice gap that changes the local symmetry of Er3+ ions. The phase composition and morphology of phosphors were analyzed by X-ray diffraction and scanning electron microscopy (SEM). The product exhibited Er3+ ion characteristic emission under 1550 nm excitation, and its luminescence mechanism was studied. This work provides a new idea for improving the luminescence intensity of up-conversion luminescent materials (UCL) under 1.5 μm excitation.

A sequence of NaCaGd(WO4)3:Tb3+,Eu3+ phosphors were prepared via a high temperature solid state reaction method. XRD, Rietveld refinement and SEM were carried out to identify the crystalline phase and morphology. The photoluminescence properties of as-synthesized phosphors excited by ultraviolet light were studied in detail. According to the photoluminescence emission spectra and fluorescence decay curves, efficient energy transfer occurred in these Tb3+, Eu3+ co-doped NaCaGd(WO4)3 phosphors. The energy transfer efficiency reached up to 92.267% when the doping concentration of Eu3+ ions reached 0.4 mol, and the dominant energy transfer mechanism was determined to be the dipole–dipole interaction. The color tunability can be realized from green to red by adjusting the Tb3+/Eu3+ doping ratio. Moreover, the representative NaCaGd(WO4)3:0.6Tb3+,0.1Eu3+ sample exhibited excellent thermal stability, and their emission intensity at 423 K still maintains about 84.7% of that at an initial temperature of 303 K. Ultimately, the as-packaged white LED device exhibited an outstanding correlated color temperature (CCT) of 4505 K and a color rendering index (Ra) of 87.3. The results mentioned above show that all the obtained phosphors are promising candidates in the fields of display devices and pc-WLEDs.

Fluoride-based doped Er3+, Yb3+ up-conversion (UC) luminescent materials were prepared via a traditional high-temperature solid-phase method. The optimum sintering temperature and holding time of phosphors were 625 °C and 1.5 h, respectively. When the molar ratio of Er3+/Yb3+ is 1:9, the phosphor shows the highest luminescence intensity. Simultaneously, NaF is used as the charge compensator and flux, which has vital effects on the luminescent properties; when the doping amount is 15 at.%, the luminescence intensity reached a maximum. The UC emission spectra of samples compose with three emitting peaks under the excitation of a 980 nm laser, including two green color-emitting peaks with a strong emission at 540 nm and a weaker emission at 521 nm and a red color emitting peak at 651 nm corresponding to the 4S3/2 → 4I15/2, 2H11/2 → 4I15/2, and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The optimal CIE coordinate of the phosphor is (0.2925, 0.6896). These results indicate that solid solution green UC phosphors with higher purity was synthesized. These results indicate that due to the excellent physical and chemical stability of fluoride-based doped Er3+, Yb3+ solid solution up-conversion phosphors, it may have potential applications in display devices, optical communications, and biosensors.

Novel up-conversion luminescent SrGd2(WO4)2(MoO4)2: Yb3+/Tm3+/Ho3+ nano-crystals were synthesized by hydrothermal method. The composition ratio of rare earth had been investigated. It indicated that when CYb3+ = 10 mol% and CYb3+/CTm3+/CHo3+ = 10:1.5:2, the emission intensities were the highest. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and up-conversion luminescence spectra were used to characterize SrGd2(WO4)2(MoO4)2: Yb3+/Tm3+/Ho3+ nano-crystals and they showed that the sample had high degree of crystallinity, the sample was tetragonal system, and the grain size of the sample was about 56 nm. Three emission peaks, including blue emission peak, green emission peak and red emission peak were observed at 477, 543 and 651 nm corresponding to 1G4 → 3H6 and 1G4 → 3F4 transitions of Tm3+, 5F4 → 5I8 and 5F5 → 5I8 transitions of Ho3+ respectively. All the emission peaks were observed by excitation of 980 nm semiconductor laser. The relationship between up-conversion intensity and excitation power revealed that blue emission at 477 nm was a three-photon absorption process, green emission at 543 nm and red emission at 651 nm was a two-photon absorption process. The quantum yields of the sample were near 3.2%.

A series of Y2.94-xLuxAl4GaO12: 0.06Ce3+ phosphors were prepared by the conventional solid-state reaction method. It was confirmed that the phosphors exhibit cubic garnet crystal structures by XRD and Rietveld refinements. The phosphors show an intense broad emission band from 475 nm to 650 nm, which attributed to the 5d→4f transitions of the Ce3+ ions under the excitation of 450 nm. Simultaneously, obvious blue shift is observed from 518 nm to 497 nm with increasing Lu3+ concentrations from 0 to 2.94. With the increase of Lu3+ concentrations the emission intensity increases and reaches to the maximum for x = 2.5. By optimizing Lu3+ concentration, the quantum efficiency up to 89.8% is obtained. The emission intensity at 453 K is up to 92% of that at room-temperature indicating a weak thermal quenching and a superior thermal stability. These results indicate that the phosphor can be used in blue LED-Chip based white LEDs in the future.

Aluminosilicate phosphors have been successfully applied in laser technology and fluorescent lamps due to their high luminescence properties and excellent chemical stability. Consequently, research on novel aluminosilicate phosphors has a good application prospect. Rare earth (RE) ions doped SrAl2Si2O8 phosphors were prepared by solid-phase method. Excited at 350 nm, the phosphor doped with Dy3+ ions emits a blue light peaking at 482 nm and an orange light peaking at 575 nm, respectively, and its optimum doping concentration is 0.8 at.%. At the NUV excitation of 377 nm, the phosphor doped with Tb3+ ions shows emission peaks at 489 nm, 544 nm, 585 nm and 623 nm, and the luminescence intensity is the strongest when the content of Tb3+ is 9 at.%. The concentration quenching mechanism of Dy3+ and Tb3+ RE ions is the electric dipole–dipole interaction. For SrAl2Si2O8:Tb3+, Sm3+ phosphors, the energy transfer efficiency is 85.4%, and the mechanism is electric dipole–quadrupole interaction. For SrAl2Si2O8:Dy3+ and SrAl2Si2O8:Tb3+, Sm3+ phosphors, the best CIE coordinates are (0.275, 0.308), (0.316, 0.386). The consequences display that RE ions doped single matrix SrAl2Si2O8 phosphors can achieve effective white light emission and have high application value in white LEDs.

A series of emission-tunable Ca9Y(PO4)7:Eu2+, Mn2+ nanophosphors were synthesized by the hydrothermal method. X-ray diffraction (XRD), photoluminescence (PL), Rietveld refinement and transmission electron microscopy (TEM) were used to characterize the samples. The results showed that the pH value played a key role in determining the morphology of nanophosphors. With the increase of pH values in the initial solution, the morphologies of samples changed from rod-shapes to ball-shapes. And the decrease of aspect ratios accompanies a change in luminescence properties. The energy transfer from Eu2+ to Mn2+ in Ca9Y(PO4)7 was achieved due to the electric multipolar interaction of the electric dipole-quadrupole mechanism, and the critical distance (Rc) between them was calculated by the concentration quenching method.

A series of Na2MMg(PO4)2:Eu2+ (M = Ca/Sr/Ba) phosphors were synthesized by the high-temperature solid-state reaction. X-ray diffraction (XRD), photoluminescence (PL) and GSAS structural refinement were used to characterize the samples. Rietveld refinements of powder X-ray diffraction patterns of Na2MMg(PO4)2 confirm that the structure of Na2MMg(PO4)2 consist of stacking along the [001] direction. The M2+ cations are located within the interlayer space, while Na+ is found in a mount of cavities bounded to the layers. Upon excitation at 350 nm, the phosphors exhibit the asymmetric broadband emission peaked at about 392 nm attributed to the 4f65d1→4f7 transitions of Eu2+. It is found that the energy transfer occurred mainly by the electric dipole-dipole interaction according to the Eu2+ concentration quenching mechanism. Moreover, when Ca2+ sites are substituted by Sr2+ or Ba2+, the Eu2+ emission band shifts to a longer wavelength initially and then returns to a shorter wavelength. In particular, 89.5% of the room-temperature emission intensity is still maintained at 500 K, indicating a good thermal stability. The obtained results suggest that the phosphor could be a potential candidate for applications in white light-emitting diodes.

The NaCaGaSi2O7:Ce3+、NaCaGaSi2O7:Tb3+ and NaCaGaSi2O7:Ce3+/Tb3+ phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by X-ray diffraction (XRD), fluorescent decay times, photoluminescence (PL) emission and excitation spectra including temperature-dependent PL properties. The effects of Ce3+ singly doped and Ce3+/Tb3+ co-doped concentrations on the structure, luminescence properties and energy transfer of NaCaGaSi2O7 phosphors were studied in detail. The results indicated that the energy transfers between Ce3+ and Tb3+ in the host occurred mainly via a dipole-dipole mechanism, and the critical distances of the ion pairs (Rc) were calculated by the quenching concentration method and spectral overlap method. The Ce3+ emission intensity and decay lifetimes decrease with the raise of Tb3+ concentration in NaCaGaSi2O7:Ce3+/Tb3+ samples. The above results indicate that NaCaGaSi2O7:Ce3+/Tb3+ can be a candidate as a host material for solid-state lighting and display fields.

In this study, based on the intra-cavity pumped dual-wavelength theoretical model, a reabsorption effect is introduced into a quasi-three-level laser, and a new theoretical model of a dual-wavelength laser with reabsorption effect is presented. Through experiments, the output characteristics of no gain competition 912 nm and 1064 nm dual-wavelength lasers with Nd:GdVO4 and Nd:YVO4 are presented for the first time. Results showed that at an incident pumping power of 38.9 W, the total output power was generally higher than at 3.6 W (1.4 and 2.2 W at 912 nm and 1064 nm, respectively) and the overall optical-to-optical efficiency was > 17%. The fluctuations in the output powers of the 912 nm and 1064 nm lasers were 1.62 and 2.18%, respectively. However, the fluctuation in the total output power was only 0.28% at a pumping power of 27.7 W. The laser mode was TEM00, and the measured M2 values for 912 nm and 1064 nm lasers were 1.35 and 1.28, respectively, under a pumping power of 30 W.

Due to the limited availability of slip systems, deformation twins have to play an additional role to accommodate strain in developing plastic deformation and undoubtedly influence the mechanical properties of materials with hexagonal structure. Therefore, understanding the interfacial characteristic of deformation twin and interaction behavior between different twin variants during plastic deformation is crucial to microstructural design, processing and application of hexagonal close-packed (hcp) materials. In the present study, { 11 2 ¯ 2 } twinning behavior in deformed titanium, with an emphasis on the misorientation across { 11 2 ¯ 2 } twinning boundary and the interaction between two { 11 2 ¯ 2 } twin variants sharing the same [ 10 1 ¯ 0] zone axis, is investigated by a combination of electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The results reveal that the actual value of misorientation across { 11 2 ¯ 2 } twinning boundary is not always equal to the theoretical one. Also, a distinctive phenomenon of one twin penetrating into the interior of the other twin, which is not observed when two { 10 1 ¯ 2 } twins encounter to each other, is discovered when the interaction between two { 11 2 ¯ 2 } twins takes place. Accordingly, the possible mechanisms behind such phenomena are proposed and discussed. These findings are expected to provide an insight into understanding the twinning behavior in hcp metals.

Deformation twins usually play an important role in plastic deformation and undoubtedly influence the mechanical properties of hexagonal close-packed (hcp) materials. Due to the rotated crystallography lattice of the twinned region, the dislocation activity within the twin may differ from that inside the matrix. Thus, understanding the origin and characteristic of these dislocations within the twin would be crucial to microstructural design, processing and application of hcp materials. In the current work, the characteristic of dislocations activated in the grain containing 11 2 ¯ 2 twins in deformed titanium has been investigated by transmission electron microscopy. Multiple type dislocations, including 〈a〉, 〈c〉 and 〈c+a〉 type dislocations, are characterized inside the twin. In contrast, only 〈a〉 type dislocations are detected within the corresponding matrix. In addition, abundant dislocation lines presenting a zigzag feature are found within the twin during deformation. According to these experimental observations, the possible mechanisms responsible for such dislocation features within the twin are proposed and discussed.

Ca2NaMg2V3O12 (CNMV):Ln3+ (Dy3+, Sm3+) phosphors were successfully prepared by high temperature solid-state method. The effect of different Ln3+ concentrations on the luminescent properties of phosphor was investigated. General structure analysis system (GSAS) shown Ln3+ ions occupied Ca2+/Na+ sites. CNMV:Ln3+ (Dy3+, Sm3+) had broad excitation bands at 200–450 nm and broad emission bands at 400–700 nm. Under 365 nm excitation, CNMV:Dy3+ samples show two dominant emission peaks at around 480 nm and 575 nm, which is corresponding to 4F9/2-6H15/2 and 4F9/2-6H13/2 transitions of Dy3+, CNMV: Sm3+ samples show three emission peaks, which is corresponding to the 4G5/2-6HJ/2 (J = 5,7,9) transitions of Sm3+. The energy transfer (ET) mechanism could be judged as an electric multipole interaction with their quenching concentration and critical distance. ET efficiency (ETE), lifetime, quantum efficiency (QE), color coordinates and good thermal stability were reported. Emitting-color tended to near white light when adjusting Ln3+ concentration.

The fatigue fracture was characterized and the fracture behavior was analyzed, using scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD), the fatigue tests of two strain amplitude at room temperature were 0.5% and 1.0% respectively, and the results showed that the fatigue deformation of different strain amplitude produced two typical fatigue fracture morphology, and when the strain amplitude was 1.0%, fatigue fracture mechanism of AZ31 magnesium alloy induced by $$\{ 10\bar{1}2\}$$ twins, when the strain amplitude is 0.5%, it was induced by $$\{ 10\bar{1}2\} - \{ 10\bar{1}2\}$$ double twins. In the present study, the average thickness of primary twin is ~ 20 μm at amplitude of 0.5% and ~ 80 μm at amplitude of 1.0%. The thickness of $$\{ 10\bar{1}2\}$$ primary twins was large enough to activate $$\{ 10\bar{1}2\} - \{ 10\bar{1}2\}$$ secondary twins at a high strain amplitude, while the thickness of $$\{ 10\bar{1}2\}$$ primary twins was too narrow to activate $$\{ 10\bar{1}2\} - \{ 10\bar{1}2\}$$ secondary twins at a low strain amplitude.

SrB2Si2O8: Eu2+/Ce3+ co-doped phosphors were synthesized via conventional high temperature solid state reaction method. The best rare earth doping SrB2Si2O8 phosphors were obtained at 950 °C for 6 h. For SrB2Si2O8: Eu2+, a large broad band locating at 440 nm corresponding to the 4f65d-4f7 (8S7/2) transition. The optimal concentration of Eu2+ is 8 at.%, its concentration quenching is due to dipole–dipole interaction. Under UV excitation of 320 nm, SrB2Si2O8: Ce3+ phosphor demonstrates a strong emission peak located at 373 nm. By Gaussian fitting, the emission of the sample peaking at 367 nm (27223 cm−1) and 396 nm (25270 cm−1) corresponding to the transition 5d–4f (2F5/2) and 5d–4f (2F7/2), respectively, the best doping concentration of Ce3+ is 0.6 at.%. Simultaneously, a series of Sr1−xB2Si2O8: xEu2+, Ce3+ phosphors were studied, results indicating that the emission intensity of Ce3+ ions decreases with the increasing of Eu2+ concentration, when the doping concentration of Eu2+ reaches 1.0 at.%, the emitting intensity is 2.1 times higher than that of the single doped Eu2+. The energy transfer efficiency among Ce3+ and Eu2+ ions is calculated to be as high as 93.4%, which is caused by the dipole–dipole resonant type from Ce3+ to Eu2+.

The effects of a micro-twin lamellar structure on the mechanical properties and fracture morphology of AZ31 Mg alloy have been investigated through impact test, tensile test, and SEM observation of the failure surface. A hot-rolled AZ31 Mg alloy sheet was subjected to dynamic plastic deformation with the aim of introducing a {10 1 ¯ 2} twin lamellar structure prior to tee tensile test, because dynamic plastic deformation with a high strain rate (4–6 × 102 s–1) can activate a greater number of deformation twins in AZ31. Compared with the mechanical properties of hot-rolled and annealed Mg alloy before dynamic plastic deformation, it was found that the tensile yield stress and maximum flow stress of the AZ31 Mg alloy increase after dynamic plastic deformation, and ductility improves under tension in the range 0–30°. Based on the analyses of microstructure and fracture morphology, the phenomenon can be ascribed to the fact that the micro-twin lamellar structure can refine the matrix grain and render the microstructure more homogeneous.

The Na3LuSi2O7:Ce3+ and Na3LuSi2O7:Ce3+, Tb3+ phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by X-ray diffraction (XRD), Photoluminescence (PL) emission and excitation spectra. The effects of Ce3+ singly doped and Ce3+/Tb3+ codoped concentrations on the structure, luminescence properties and energy transfer of Na3LuSi2O7 phosphors were studied in detail. The results indicated that the energy transfers between Ce3+ and Tb3+ in the host occurred mainly via a dipole-quadrupole mechanism, and the critical distances of the ion pairs (Rc) were calculated by the quenching concentration method and spectral overlap method. Based on the good PL properties adjusting the doping concentration of the activators (Ce3+,Tb3+) might be promising as a host material for solid-state lighting and display fields.

This review focuses on grain growth behaviors and the underlying mechanisms of bulk electrodeposited nanocrystalline nickel and nickel-iron alloys. Effects of some important factors on grain growth are described. During thermal-induced grain growth process, grain boundary migration plays a key role. For similar thermal conditions, due to grain boundary mobility with solute drag, limited grain growth occurs in nanocrystalline alloys, as compared to pure metals. Nonetheless, in the case of stress-induced grain growth process, there are a variety of mechanisms in samples having various deformation histories. As an example the grain growth of nanocrystalline nickel and Ni-20%Fe alloy with nearly the same grain-size distribution and average grain size is compared in this paper. Thermal analysis indicates nanocrystalline nickel is much more prone to rapid grain growth than nanocrystalline Ni-20%Fe alloy. Nevertheless, grain growth of nanocrystalline Ni-20%Fe is found to be more pronounced than nanocrystalline nickel during rolling deformation.

In this paper, thick 4H-SiC epilayers of 147 μm demanded for ultra-high-voltage power devices has been obtained at a high growth rate of 85 µm/h under optimized growth conditions. We have attempted to improve the quality and reduce the surface defect density of thick epilayers. The surface defect density is obviously reduced from 3.46 cm−2 to 0.85 cm−2, owing to the addition of the etching process. The effect of the etching process on the surface defect is discussed based on the measured results. The results demonstrate that the fast epitaxial growth system can grow ultra thick 4H-SiC epilayers with high quality that satisfies the requirement of ultra-high-voltage devices.

In this work, a group of NaBi(MoO4)2 phosphors doped with various Sm3+ concentrations were prepared utilizing the solid state reaction. The crystalline phases were identified by the implement of XRD as well as Rietveld refinement, and the relevant data of the optimum sample turn out to be a = b = 5.245 A, c = 11.563 A, Rp = 7.66%, Rwp = 9.64% and χ2 = 1.512. Upon the irradiation of 406 nm, all the phosphors exhibited orange-red light emission with the primary peak at 599 nm. Furthermore, the optimal doping concentration of Sm3+ ion was determined as 0.08 mol, and the mechanism of energy transfer between two adjacent Sm3+ ions was dominated by the dipole-dipole interaction. The possible lattice sites occupied by Sm3+ ions were investigated via the fitting function type of decay curves. The calculated CIE chromaticity coordinate of NaBi(MoO4)2: 0.08Sm3+ phosphor verified that its emission light was located in the orange-red region. The aforementioned results demonstrated that the NaBi(MoO4)2: Sm3+ phosphors could be used in the area of NUV-excited white light emitting diodes.

A series of Dy3+ activated Ba(YLu)2Si3O10 samples were prepared by high temperature solid-phase method. The purity of the phase was determined and the structural changes were analyzed. Under excitation at 350 nm, the BaY2Si3O10: Dy3+ phosphor shows two stronger luminescence peaks at 486 nm and 572 nm and weaker emission peak at 668 nm. In addition, with the continuous replacement of Y3+ in the matrix by Lu3+ ions, the chromaticity coordinates of samples in the system can be adjusted from the cold white region to the warm white region, and the luminescence performance of phosphors can be effectively improved. It was observed that the thermal stability of the phosphor was gradually enhanced with Lu3+ concentration increases, and the emission intensity of the BaLu2Si3O10: 0.04Dy3+ phosphor at 453 K could still maintain 83.78% of that at room temperature, which was discussed in conjunction with the Debye temperature and the rigid structure model to provide a reference for the improvement of the thermal stability performance. In addition, the increase of the concentration of Lu3+ ions doping will shorten the lifetime of phosphors due to the non-radiative energy transfer caused by the shortening of the ion distance in the lattice.

Previous studies have shown that an accurate prediction of frost heaves largely depends on the pore water pressure and hydraulic conductivity of frozen fringes, which are difficult to determine. The segregation potential model can avoid this problem, however, the conventional segregation potential is considered to be approximately unchanged at a steady state and only valid in an open system without dehydration in the unfrozen zone. Based on Darcy&rsquo, s law and the conventional segregation potential, the segregation potential was expressed as a function of the pore water pressure at the base of the ice lens, the pore water pressure at the freezing front, the freezing temperature, the segregation freezing temperature and the hydraulic conductivity of the frozen fringe. This expression indicates that the segregation potential under quasi-steady-state conditions is not a constant in a closed system, since the pore water pressure at the freezing front varies with the freezing time owing to the dehydration of the unfrozen zone, and that when the pore water pressure at the freezing front is equal to that at the base of the ice lens, the water migration and frost heave will be terminated. To analyze the possibility of applying the segregation potential model in a closed system, a series of one-sided frost heave tests under external pressure in a closed system were carried out in a laboratory, and the existing frost heaving test data from the literature were also analyzed. The results indicate that the calculated frost heave was close to the tested data, which shows the applicability of the model in a closed system. In addition, the results show the rationality of calculating the segregation potential from the frost heaving test by comparing the potential with that calculated from the numerical simulation results. This study attempted to extend the segregation potential model to freezing soil in a closed system and is significant to the study of frost heaves.

In this work, a series of red emitting Lu3Te2Li3O12: Eu3+ phosphors were synthesized for the first time by high temperature solid state reaction. The structure was characterized by X-ray diffraction. The excitation spectra, emission spectra and CIE chromaticity coordinate were studied. The phosphors show strong red emission at 611 nm due to the 5D0-7F2 transition of Eu3+ ions. The optimal doping concentration of Eu3+ in LTL host is x = 0.5 due to the concentration quenching mechanism of dipole-dipole interaction. The CIE chromaticity coordinates of the LTL: 0.5Eu3++ phosphor is (0.644,0.355), and the purity of the color is up to 93.61%. The phosphor can be considered as a potential red-emitting candidate for near UV WLEDs.

Yttrium aluminum garnet (Y3Al5O12, YAG) ceramics with a relative density of about 99.5% were fabricated by solid-state reaction and pressureless sintering using commercial α-Al2O3 and Y2O3 powders as raw materials in air. The effect of different sintering additives, e.g. tetraethyl orthosilicate (TEOS), MgO and TEOS + MgO, on the relative density and mechanical properties of the YAG ceramic samples were investigated. When the dopant content of TEOS exceeded 0.5 wt.%, a sudden grain growth appeared, as well as a residual second phase located in triangle grain boundary. MgO was more effective as a sintering additive than silica in promoting the densification of the YAG ceramics. The relative density of the ceramics gradually decreased with the increase of MgO doping content and fixed TEOS content. The mechanical properties of the YAG ceramics fabricated by pressureless sintering in air at 1600–1710°C were tested. The fracture surface morphology of the MgO-doped ceramic samples was mainly transgranular, whereas the TEOS-doped samples were mainly intergranular.

Microstructural stability is an important issue for nanocrystalline materials to be practically used in many fields. The present work shows how microstructure evolves with rolling strain in pre-annealed electrodeposited nanocrystalline nickel containing an initial strong fiber texture, on the basis of X-ray diffraction line profile analysis as well as transmission electron microscopy observation. The influence of shear strain on microstructural stability of the metal/roll contact interface is compared with that of the metal/metal contact interface; the latter would be closer to deformation in plane strain compression. From the statistical microstructural information, together with experimentally observed microstructure of deformed grains after the final rolling pass, it seems fair to conclude that the microstructure of the metal/metal contact interface is more stable during pack rolling than that of the metal/roll interface.

Y2.85Al5-ySiyO12-(3x-y)/2Nx: Ce3+0.15 phosphors were prepared using aluminum nitride (AlN) and silica (SiO2) as the sources of N and Si by the high temperature solid state reaction method. XRD patterns of the phosphors present a pure phase but have a slight translation compared to the standard card of Y3Al5O12(YAG). The Al3+-N3- bonds and Y3+-N3- bonds were detected by the analysis of X-ray photoelectron spectroscopy (XPS). The tendency to bond with N3− ions for the cations changes from Y3+>Ce3+ to Ce3+>Y3+ for the samples introduced SiO2. Photoluminescence spectra (PL & PLE) show that the crystal field splitting (CFS) and the nephelauxetic effect (NE) play a conflicting role in spectral shifting. When x = y, NE plays a major role and the emission red shift reaches the maximum. The thermoluminescence tests (TL) confirm that temperature quenching of the phosphors is caused by the thermally-activated crossover process.

A hot-rolled AZ31Mg alloy sheet was subjected to dynamic plastic deformation parallel to the rolling direction, and microstructural evolutions and mechanical properties of the deformed samples were examined. It has been found that dynamic strain rate could facilitate {10-12} twin nucleation and growth and leads to a lower yield stress of about 20 MPa and an early end to twinning characteristic (happening at a strain point of about 6%) shown in the stress–strain curve. {10-12} twinning mechanism dominates the early plastic deformation; but when plastic strain exceeds ~ 9%, dislocation–slip mechanism instead of {10-12} twinning dominates the later plastic deformation. And this premature transformation of the dominant deformation mechanisms from {10-12} twinning to dislocation slip is caused by dynamic strain rate. The effect of dynamic strain rate on the number of twin nucleations remains unclear, and the more systematic researches are needed in the future.

In the present work, the influence of pre-induced { 10 1 ¯ 2 } twin characteristics on detwinning activation in a basal texture magnesium alloy is systematically investigated by a combination of electron backscatter diffraction technique and mechanical tests. Samples containing pre-induced { 10 1 ¯ 2 } twin variants with different morphological characteristics are prepared by pre-strain path change tests comprised two pre-strain paths: (i) compression along the rolling direction of magnesium alloy plate; (ii) tension along the normal direction of magnesium alloy plate. In the former case, a single { 10 1 ¯ 2 } twin variant or a { 10 1 ¯ 2 } twin pair is formed in one grain. While, multiple { 10 1 ¯ 2 } twin variants are usually activated simultaneously in one grain in the latter case. During subsequent compression along normal direction, detwinning process is effectively retarded for the samples containing multiple { 10 1 ¯ 2 } twin variants in one grain. Meanwhile, the yield stress of corresponding samples is enhanced as well, compared to that of the samples containing a single { 10 1 ¯ 2 } twin variant or a { 10 1 ¯ 2 } twin pair in one grain. According to these experimental features, the possible reasons behind such phenomena are proposed and discussed.

Tb3+ doped Na3LuSi2O7(NLSO) phosphors were prepared by a solid state reaction technique. The crystal structures and the influence of Tb3+ concentration on the photoluminescence, cathodoluminescence of the phosphors were investigated. Two groups of emission lines had been observed, which were corresponding to Tb3+ 5D3 → 7FJ (J = 6, 5, 4, 3) and 5D4 → 7FJ (J = 6, 5, 4, 3) transitions. The physical mechanisms for excitation, emission, concentration quenching and the cross-relaxation mechanism between the 5D3 and 5D4 emission were investigated in detail. Cathodoluminescence properties were also studied for the optimized samples as a function of filament current. The Commission International de I-Eclairage (CIE) chromaticity coordinates were calculated for the NLSO:Tb3+ phosphors.

MgxZn1−xO has attracted more attention due to its tunable direct band gap, which can make it tune optical absorption from near to the deep ultraviolet range. The synthesis temperature has important influence on the regulation of bandgap. So, we studied the effects of synthetic temperature on properties in this work. Mg0.3Zn0.7O thin films were grown on quartz substrates by sol–gel method from 700 to 1000 °C. The effects of substrate temperatures on the structure and optical properties were investigated. The X-ray diffraction patterns showed that all the alloy films grew along (100), (101), (002) orientation, and belonged to a hexagonal wurtzite structure. With increase of the growth temperature, the diffraction intensity of the (002) peaks increase and the film along c-axis oriented growth was formed at 900 °C. The optical band gap enlarged gradually from 3.4628 to 3.5014 eV with the increase of the growth temperature and the film has the lowest resistivity of 5.248 × 107 Ω cm at 900 °C. The photo-electric properties of the film calcinated at 900 °C were studied. A maximum photocurrent is 1.54 µA at 20 V bias and photo-responsivity peaking at 330 nm is 1.66 A/W at 30 V bias, respectively.

The relationship between microstructure and tensile behaviors of fatigued AZ31 magnesium alloy was investigated. Axial fatigue tests were performed on PLG–100 fatigue machine at stresses of 50 and 90 MPa. Tensile samples were cut from the fatigued samples, named as L-sample and H-sample respectively, and the O-sample was cut from original rolled AZ31 alloy. The EBSD and TEM were used to characterize the microstructure. It is found that the twinning–detwinning was the main deformation mechanism in high stress fatigue test, while dislocation slipping was dominant in low stress fatigue test. After fatigue tests, the average grain size of the L-sample and H-sample decreased to 4.71 and 5.33 μm, and the tensile and yield strength of the L-sample and H-sample increased slightly. By analyzing SEM images, the ultimate fracture region of the L-sample consisted of dimples, while there were many microvoids in the ultimate fracture region of the H-sample. Consequently, the tensile behaviors of fatigued magnesium have a close relationship with microstructure.

Up-conversion luminescence materials sensitive to 1550 nm are of broad application prospects. One of the most important properties is that the phosphor should be ultrafine and dispersed well with excellent luminescence intensity in order to meet the matching application requirements of those image and detection devices. The low-temperature combustion synthesis method, a most popular method for the synthesis of ultrafine oxides, was adopted to synthesize the Er3+ doped lead–sodium–yttrium–fluoride phosphor using glycine as the fuel. Orthogonal experiments were carried out to determine the optimum cation molar-proportion. Dispersing agent (NH4)2SO4 was adopted to improve the dispersion state of the ultrafine phosphor and the high-temperature solid-state reaction process was performed to optimize its morphology and luminescence properties. The sample presents Er3+ characteristic emission peaks and its luminescence mechanism excited at 1550 nm was discussed.

Y3−yAl5−xGaxO12:Ce3+y phosphors were prepared by high temperature solid state reaction method. The crystal structures, the influence of Ga3+ concentration on the photoluminescence (PL), cathodoluminescence, thermal stability and morphology of the phosphors were studied in detail. The results indicated that diffraction angle of the samples decreased gradually with the increase of Ga3+ ions content in XRD pattern. The emission peak of the spectra show a progressive blue-shift, the intensity increased first and then decreased and the optimal Ga3+ concentration in Y2.94Al5−xGaxO12:Ce3+0.06 phosphors is x = 0.75. The critical concentration of Ce3+ in YAGG:Ce3+ phosphors is affected with the ratio of Ga3+ to Al3+ and the Y2.9Al4.25Ga0.75O12:Ce3+0.1 phosphor showed the best performance on PL. However, the optimum concentration of Y3−yAl5−xGaxO12:Ce3+y phosphors is x = 1.5 and y = 0.04 when they were excited by cathode ray.

YVO4:Bi3+,Ln3+ (Ln = Dy, Sm, Eu) phosphors were successful synthesized by microwave sintering method, and characterized by X-ray powder diffraction, scanning electron microscope, photoluminescence spectra, lifetime, quantum efficiency and general structure analysis system structure refinement. Refinement results indicated that the introduced ions occupy the sites of Y3+. Under 275 nm excitation, the luminescent intensity of YVO4:Bi3+ samples reach the maximum when Bi3+ concentration is 0.02, the broad excitation spectrum of YVO4:Bi3+ has a strongest peak at near 343 nm. Doped Bi3+ can effectively improve the emission intensity of YVO4:Ln3+. The energy transfer mechanism of Bi3+ → Ln3+ was dipole-quadrupole mechanism of electric multipole interaction. The critical distance (Rc) between Ln3+ and Bi3+ were calculated by concentration quenching method. Emitting color of YVO4:Bi3+,Ln3+ phosphors were tunable by adjusting Ln3+ content. In a word, the material has a good application prospects on light emitting diodes.

Well-crystallized NaREF4: Yb3+, Er3+ (RE = Y, Lu, La, Gd) phosphors were synthesized by a solid-state reaction method. X-ray diffraction characterization showed that the synthesized samples were all pure hexagonal phase after a calcination process on the as-prepared precursors at 550 °C for 2 h by using Na2CO3 as a fluxing agent. Upconversion spectral analysis showed that under a 1550 nm laser diode excitation, the samples emitted dominant green emission centered at 540 nm and red emission centered at 654 nm, which corresponded to the 2H11/2/4S3/2→4I15/2 and 4F9/2→4I15/2 transition of Er3+ ions, respectively. Color-tunable upconversion luminescence was realized by the variation of Yb3+/Er3+ doping concentration and the types of the host materials, indicating the synthesized hexagonal Yb3+ and Er3+ co-doped NaREF4 phosphors potential applications in many fields, especially in biological imaging and detection.

MgZnO as a type of wide band-gap semiconductor has become a vital studied orientation in Ultraviolet (UV) detector. Nanometer size Mg0.2Zn0.8O films with homogeneous particle distribution were synthesized by sol-gel method and a wide UV respective photo-detector covered solar blind to near UV range has been obtained. The structure, surface morphology and properties of Mg0.2Zn0.8O films and photo-electric properties of detector have been studied. The thin film exhibits a strong (002) orientation growth property and all the Mg2+ ions have entranced into ZnO lattice. The average crystalline size of film is 30 nm and close to 70% particle size is between 25 nm and 35 nm. The films display a high transmittance close to 70%. The Eg of the film is 3.47 eV corresponding to absorption edge begins to 357 nm and the first exciton absorptive peak is at 346 nm. At various wavelength light illumination, the photo-detector with a simple metal/semiconductor/metal (MSM) structure shows a linear I-V relation. The spectral response is a broad band around between 250 nm and 400 nm peaking at 336 nm. The good responsivity arrives to 0.55 A/W, which is more than other reports.

Mg2+-Ge4+ ions substituted YAG: Ce3+ phosphors (Y3Al5-2xMgxGexO12: Ce3+) were prepared by high temperature solid state reaction method. X-ray diffraction (XRD), Scanning election microscope (SEM), Photoluminescence (PL) spectra and so on were used to characterize the samples. The effects of Mg2+-Ge4+ concentrations on the morphology, structure, luminescence properties, fluorescence lifetime and white LED performance of YAG: Ce3+ phosphors were studied in detail. The results indicate that Mg2+-Ge4+ ion pairs can partially substitute the Al3+ ions of YAG successfully. With the substitution, the garnet crystal structure remains unchanged. However the emission spectra show a progressive red-shift, from 528 to 552 nm (about 24 nm). The lifetime decreased rapidly from 84 to 26 ns. In particular, the correlated color temperature (CCT) decreases gradually from 6798 to 3261 K and the color rendering index (CRI) increases from 76.5 to 89.3 with the increasing of the incorporation content of Mg2+-Ge4+ ion pairs.

Deformation twins usually play an important role in plastic deformation and undoubtedly influence the mechanical property of hexagonal close-packed (hcp) metals. Understanding the interfacial features of twinning boundaries and their evolution during the plastic deformation is crucial to hcp materials design, processing and application. In this work, the interfacial characteristics of $$ \{ 10\bar{1}1\} $$ contraction twin in deformed magnesium alloy are investigated by means of electron back-scatter diffraction, transmission electron microscope and high-resolution TEM. The results show that the misorientation angle across the boundaries of $$ \{ 10\bar{1}1\} $$ contraction twin can deviate from the theoretical value $$ \left( {56.2^\circ \left\langle {11\bar{2}0} \right\rangle } \right) $$ , resulting in that the $$ \{ 10\bar{1}1\} $$ twinning planes of the twin crystal and the matrix crystal do not coincide any longer. Multiple dislocation activities within the $$ \{ 10\bar{1}1\} $$ contraction twin and interfacial defects located on the $$ \{ 10\bar{1}1\} $$ twinning plane are also characterized. According to these experimental features, a possible mechanism responsible for such deviation phenomenon is proposed. In addition, the similar deviation phenomenon is also observed in the $$ \{ 10\bar{1}1\} $$ – $$ \{ 10\bar{1}2\} $$ double twin system.

The typical fracture morphology of the Mg-3Al-1Zn alloy after cyclic deformation was investigated using optical microscopy (OM), and an electron back-scatter diffraction (EBSD). A novel finding of this study is that large number of stripe-like laminas were found within the primary { 10 1 ¯ 2 } tensile twins in the crack initiation and crack propagation regions. It is shown that these laminas primarily result from { 10 1 ¯ 2 } − { 10 1 ¯ 2 } twinning during cyclic deformation. According to the results and combined with theoretical analysis, the formation of { 10 1 ¯ 2 } − { 10 1 ¯ 2 } twins are largely contributing to the local strain accommodation caused by different twin variants.

In this study, Mg single crystals (99.99% purity) were subjected to focused ion beam (FIB) bombardment perpendicular and parallel to the c-axis of the hexagonal close packed (HCP) lattice respectively. The research results indicate that the {1 0 −1 2} twin nucleation induced by FIB micro-stress in magnesium single crystal is dependent on the applied ion current and the crystal orientation. The incident Ga + ions dose increases with ion current, which would enhance the FIB loading micro-stress. And when the FIB incident direction is parallel to the close-packed (0 0 0 1) plane, there would be more ion-atom interactions during FIB bombardment. Both processing mechanisms could lead to larger precipitate-matrix misfit area and further microstructure damage, which might eventually facilitate {1 0 −1 2} twin nucleation.

Hydraulic conductivity of frozen soil is indispensable for describing water flow process in freezing soils. However, this conductivity is difficult to measure in the laboratory. So, the objective of this study is to propose a simple and smooth hydraulic conductivity model for saturated frozen soil based on the soil freezing characteristic curve (SFCC). Considering that the volume of pore water approximately represents the pore volume, the distribution of effective pore radii changed as a function of temperature was determined by combining the SFCC and the Gibbs–Thomson equation. Based on the distribution of effective pore radii, Hagen-Poiseuille equation, Darcy’s law, relative hydraulic conductivity and tortuosity, a simple and smooth hydraulic conductivity model for saturated frozen soil based on the SFCC was proposed. To illustrate the model performance, eight existing experimental cases were analyzed. The results showed that predictions considering the three different tortuosity formulations were in good agreement with the tested data; the results were worse when not considering the tortuosity and the results were best when considering the tortuosity τ F = B / r b 2 . Moreover, the predictive modeling power was related to the tortuosity function. Furthermore, the model was further compared with the previous models, the results of which showed the better performance of the proposed model. The model is quite simple and timesaving to use when the SFCC and the saturated hydraulic conductivity are available. This result provides a new idea for developing the hydraulic conductivity model of saturated frozen soil.

A series of Y2-x-yMg3Ge3O12: xDy3+, yTb3+ samples were manufactured by high temperature solid phase method. XRD test and Rietveld refinement clarified the phase purity of the samples. When the excitation wavelength is 352 nm, the energy transfer efficiency is 57.74%, and q-q interaction is the main energy transfer mechanism of Dy3+-Tb3+ co-doped samples. In addition, we tested the thermal stability of Y1.94Mg3Ge3O12:0.05Dy3+, 0.01 Tb3+ sample, and found that its luminous intensity at 423 K could still reach 93.86% of that at 303 K. By changing the concentrations of Tb3+, the luminescent color of the samples could also be changed from blue-white light to yellow-green light. These results indicate that Y2Mg3Ge3O12 co-doped with Dy3+ and Tb3+ is expected to be applied in the field of white light LEDs.

Anomalous basal stacking faults have frequently been observed inside 10 1 − 2 twins in deformed hcp metals. In this work, we report transmission electron microscopy observation of basal stacking faults inside 10 1 − 1 twins. These stacking faults present similar characteristics to those inside 10 1 − 2 twins. To reveal the formation mechanism, we performed atomistic simulations. The results show that the stacking faults are not mediated by partial dislocations. Lattice transformation analysis based on classical twinning theory shows that very large atomic shuffles (~ 0.16 nm) perpendicular to the twinning shear are required for twinning and responsible for the formation of these stacking faults.

In order to prepare various Y2.94Al4−xSixGaO12: 0.06Ce3+ phosphors, a traditional approach to solid-state reaction was adopted. XRD and Rietveld were refined to confirm the cubic garnet crystal structure of phosphors. Besides, the substance displayed a wide mission band varying between 475 nm and 650 nm due to the 5d→4f transitions of the Ce3+ ions as excited by a 450 nm wavelength. Furthermore, as the Si4+ concentration increases from 0 to 0.6, we can observe a blue shift in the emission spectrum from 510 nm to 502 nm. The emission intensity at 453 K is still 88% of that at room temperature. At the same time, through the auxiliary calculation of activation energy, the advantages of thermal stability and the weakness of thermal quenching are explained. Surprisingly, a demonstrational application confirmed the excellent capability of optical data retention in encoding/decoding the material, including a designed bar code and graphic patterns. It is suggested that phosphor is applicable for the development of white LEDs based on the blue LED-chip. In particular, when some unexpected circumstances occur and lighting conditions suddenly break down, LED with long afterglow performance can alleviate the discomfort caused by the change. It is also expected to move forward the study on Long-lasting phosphorescence (LLP) materials and their practical application in optical storage.

A variety of Dy3+ single-doped and Dy3+, Eu3+ co-doped NaBi(WO4)2 phosphors were synthesized by the high temperature solid state method. The XRD patterns and Rietveld refinement measurement were operated to identify the crystalline phases. When the NaBi(WO4)2: 0.08Dy3+, yEu3+ phosphors were excited by 352 nm light, the energy transfer efficiency can be reach to 72.576% and the type of energy transfer mechanism was dominated by the dipole-dipole interaction. The thermal stability of specific NaBi(WO4)2: 0.08Dy3+, 0.1Eu3+ phosphor was tested and the PL emission intensity at 423 K drops to about 77.2% of that at 303 K, and the warm white light can be obtained after varying the Eu3+ ion concentration. Aforementioned results manifest that these as-prepared samples are expected to be the potential single-phase phosphors used in the areas of solid state lighting.

A battery of Dy3+ single-doped and Dy3+/Eu3+ co-doped Y2Mg3Ge3O12 phosphors were manufactured by high-temperature solid-phase method. The XRD patterns were tested and Rietveld refined. When the samples were excited by 352 ​nm near ultraviolet light, the energy transfer efficiency can reach 83.2%, and the energy transfer mechanism is electric dipole-electric dipole interaction. The thermal stability of Y1.75Mg3Ge3O12:0.05Dy3+, 0.2Eu3+ was tested. When the temperature reached 150 ​°C, its luminous intensity droped to 92.4% of the initial temperature (30 ​°C). By changing the concentrations of Eu3+, white light with red light can be obtained. The above results indicate that these samples are expected to become candidate materials in the domain of solid-state lighting.

In order to promote the development of white light emitting diodes (WLEDs) with improved color reproduction, the challenge by discovering novel photoluminescence color tuning phosphors via energy transfer (ET) is essential. However, the mechanism of energy transfer among dopants and its effect on ET efficiency have not been fully understood. Therefore, the photoluminescence color tuning in a variety of matrix structures based on energy transfer always needs to be discussed further. Herein, a series of wide-ranging color tunable Li3Lu3Te2O12 phosphors doped with Tb3+/Eu3+ were synthesized by high-temperature solid-state reaction for the first time. The crystalline structure, morphology and chemical composition of as-prepared phosphors were characterized. The excitation and emission spectra, fluorescence decay curve, and the relationship among emission intensity, doping concentration of dopants and CIE coordinates were investigated in detail. The results indicate that photoluminescence color tuning from green to red was realized by designing the Tb3+→Eu3+ energy transfer in Li3Lu3Te2O12:Tb3+, Eu3+ phosphors. The approximation theory of Reisfeld and the electric multipole interaction theory of Dexter were used to analyze the ET mechanism, which reveals that the dipole-dipole and dipole-quadrupole interaction is responsible for the ET process of Tb3+→Tb3+ and Tb3+→Eu3+. In addition, the thermal stability of the as-prepared phosphors was also revealed. Unforgettably, the samples with reasonable design ratio of Tb3+/Eu3+ exhibits a wider color tuning range, excellent luminescence intensity under n-UV excitation and outstanding thermal stability comparable to commercial Y2O3:Eu3+ phosphor after surface treatment, whose emission intensity at 150 °C exceeds 70% of the initial value. In addition, a prototype WLED device was fabricated with representative phosphor and commercial blue phosphor BaMgAl10O17: Eu2+ (BAM: Eu2+), which emitted warm-white light with great color rendering index (CRI) of 84.8, softer correlated color temperature (CCT) of 3989 K and the chromaticity coordinates of (0.3647,0.3178). All the results suggest that Li3Lu3Te2O12:Tb3+, Eu3+ phosphors can be conducted as potential alternative for near ultraviolet (n-UV) pumped phosphor-converted white light-emitting diodes (pc-WLEDs).