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Halide perovskites are essential materials for hard radiation detectors at ambient temperature. To improve detector performance, charge transport must be investigated and optimized. Using photoluminescence (PL) and thermally stimulated current (TSC) spectroscopies, we investigate photogenerated charge carriers in Bridgman-grown CsPbBr3 single crystals to understand the nature of charge transport. PL spectroscopy of these halide perovskites revealed the presence of strong emission bands at the band edge, which were attributed to free or bound excitons. It is shown that a wide broadening of the excitonic linewidth in these halide perovskites arises from strong exciton–phonon coupling, which is substantially dominated by longitudinal optical phonons via Fröhlich interaction. An additional contribution due to the presence of ionized impurities was also observed. Crystals with a detectable sensitivity to high-energy gamma radiation are characterized by a higher intensity and a narrower linewidth of the principal PL peak at 2.326 eV. Defect states beyond 2.214 eV have a negative impact on detector sensitivity to high-energy gamma radiation. TSC spectroscopy reveals an array of trap levels spanning 0.15–0.70 eV, attributed to intrinsic point defects and multiple extrinsic defects involving dopants or impurities. Defects identified included Cs and Br vacancies, as well as Pb interstitials with concentrations in the 1011–1016 cm−3 range. Understanding how the synthesis process impacts the types and concentrations of the defects present is currently under investigation. Elimination or suppression of the defect/trap states should result in halide perovskite materials with longer carrier diffusion lengths and improved detector characteristics. [ABSTRACT FROM AUTHOR]

Thermally stimulated current (TSC) spectroscopy was used to characterize electronic trap states in the perovskite CsPbCl3 bulk single crystals which are promising for gamma ray detection. The TSC spectra indicate the presence of multiple traps over the temperature range from 80 K to above room temperature. The possible analytical defects identified were VCs and VCl vacancies and Pbi interstitials that have concentrations of the order of 1011−1016 cm−3 and capture cross sections of ∼10−18 cm2. A comparison of crystals grown from different ingots reveals that the concentration of defects in the crystal with an improved growth procedure is about one to four orders of magnitude less than those of a crystal from an earlier growth process. A further reduction and elimination of trap states within the perovskite ingot should lead to crystals with improved mobilities, carrier lifetimes, and detector response characteristics. [ABSTRACT FROM AUTHOR]

Recently, there has been considerable interest in x-ray and gamma ray detectors with large volume and high energy resolution that operate at room temperature. To improve detector energy resolution, the carrier mobility-lifetime product needs to be increased, and the electronic trap state concentration needs to be minimized. Defect concentrations in the part per billion range can alter the charge transport and carrier recombination lifetime. In this work, thermally stimulated current spectroscopy measurements were systematically carried out in bulk halide perovskite single crystals of CsPbBr3 over a temperature range of 80–320 K. The origins and trap parameters of CsPbBr3 crystals from the solution growth and melt growth procedures were determined and compared. Trap concentrations were ranged from 1 × 1011 to 1 × 1016 cm−3. Appreciable detector performance was observed for CsPbBr3 crystals with trap concentrations less than 1 × 1014 cm−3. The comparison of spectral responses of crystal samples grown using two different methods shows that, after purification, solution-grown crystals are comparable to melt-grown crystals in terms of low defect concentration and improved detector performance. For an improved mobility-lifetime product and enhanced spectral response to high energy radiation from fissile materials, trap states in either type of a crystal ingot must be reduced closer to 1011 cm−3. [ABSTRACT FROM AUTHOR]

The crystal structure, lattice vibration and microwave dielectric properties of 3CaO·2SiO 2 · x CaF 2 ceramics were investigated in this work. With the increasing of x value, the crystal structure of 3CaO·2SiO 2 · x CaF 2 ceramics transfers from rankinite (Ca 3 Si 2 O 7) to cuspidine (Ca 4 Si 2 O 7 F 2). The increase of the vibration energy and shrinkage of [SiO 4 ] tetrahedral unit hampers the ionic polarization and thus reduces relative permittivity (ε r). The enlarged FWHM of the Si–O stretching peak reflects a more drastic anharmonic lattice vibration, resulting in a lower quality factor (Q × f value). The Raman shift of O/F–Ca–O/F bending peak is positively correlated with the temperature coefficient of resonant frequency (τ f). The microwave dielectric properties of ε r and Q × f value (∼@11 GHz) ranging from 7.89 to 8.42, and 21805–46098 GHz, respectively. The stable complex permittivity (ε r ∗) in the frequency range of 20–110 GHz indicates that the fluoride cuspidine ceramics could be a promising candidate for microwave device applications. [ABSTRACT FROM AUTHOR]

High-flux capable semiconductor x-ray detectors are essential in various applications, but the detrimental effects of detector polarization limit their use in many cases. Here, we studied the polarization of perovskite CsPbBr3 semiconductor detectors using ultrahigh flux synchrotron x rays (106–1012 photons s−1 mm−2 at 58.61 keV). The CsPbBr3 detectors did not show immediate polarization prominently until a flux higher than 1010 photons s−1 mm−2. Using the pump-and-probe technique, we visualized the spatial and temporal effects of polarization. The polarized region, represented by reduced photocurrent, extended beyond the area under direct irradiation, and the reduced photocurrent persisted after potential de-polarization treatments. We found that stronger applied electric fields and fewer carrier traps can mitigate polarization, represented by less photocurrent deficit. By examining the detectors' current response under controlled ambient light, low, and high-flux x rays, we studied the trap filling and release behavior of CsPbBr3. We discovered that the polarization is caused by partial detector damage due to deep defects generated by ultrahigh flux x-ray irradiation. Our work provides insight into CsPbBr3 polarization under extremely intense x-ray radiation and shows that reducing crystal defects and increasing detector bias voltage are effective solutions. [ABSTRACT FROM AUTHOR]

A series of K2MnF6/KHF2 red phosphors were prepared through a low temperature way and their morphology and photoluminescence (PL) properties were investigated. The as-prepared phosphor shows an intense red emission with the strongest emission peak at 631 nm under a 454 nm excitation. Furthermore, the PL intensity and thermal stability performance, together with the quantum yields of the entitled phosphors excited under blue light are investigated and compared with relative commercial used phosphors. Finally, a bright LED with high color rendering performance of Ra = 86.8 was fabricated by using a 450 nm blue chip with YAG:Ce3+ and the as-prepared K2MnF6/KHF2 phosphor. The results indicate that the K2MnF6/KHF2 phosphors could facilitate potential application in the field of indoor lighting and backlighting. [ABSTRACT FROM AUTHOR]

The Li–Al–Si glass-ceramics were prepared by conventional glass-ceramic fabrication method. The influences of Na 2 O content on the sintering property, microstructure, and coefficient of thermal expansion were investigated. The results show that the coefficient of thermal expansion of LAS glass-ceramics can be tailored to match that of silicon by the addition of Na 2 O content. Na 2 O has a remarkable influence on the crystallinity of Li–Al–Si glass-ceramic. The coefficient of thermal expansion of Li–Al–Si glass-ceramic is thus tunable between that of glass phase and crystal phase. The Si–O bond length change in stretch vibration modes introduced by Na 2 O also contributes to the variation of coefficient of thermal expansion of the Li–Al–Si glass-ceramics. The coefficient of thermal expansion of the Li–Al–Si glass-ceramic with 1.5 wt% Na 2 O addition is about +3.34 ppm/°C at 350 °C and shows a good compatibility to that of silicon in a wide temperature range, which makes it a promising candidate for anodic bondable low temperature co-fired ceramic substrate applications. [ABSTRACT FROM AUTHOR]

The CaTi (1-x) (Al 0.5 Nb 0.5) x SiO 5 (0 ≤ x ≤ 0.1) ceramics were prepared by the conventional solid-state method. Al and Nb co-doping improved the high temperature stability of the CaTiSiO 5 material and no obvious phase transition was found at temperature up to 623 K for x ≥ 0.03. A dielectric constant of 53, dielectric loss of 0.001, resistivity of 8.5 × 1013 Ω cm, and breakdown strength of 1064.7 kV/cm was obtained for the CaTi 0.97 (Al 0.5 Nb 0.5) 0.03 SiO 5 ceramics at room-temperature. The dielectric constant is stable over a wide temperature range and a resistivity of 9.0 × 1010 Ω cm could still be achieved up to 573 K. The P-E loops measurements showed that energy storage efficiencies of 96% and 88.6% could be obtained at room-temperature and 453 K, respectively, for the CaTi 0.97 (Al 0.5 Nb 0.5) 0.03 SiO 5 ceramics. The excellent dielectric properties at elevated temperature indicate that titanite based ceramics stabilized by Al and Nb co-doping could be promising candidates for high temperature ceramic capacitors application. • The pure high-temperature monoclinic A2 1 /a phase of doped CaTiSiO 5 was obtained. • Co-doping of Al3+ and Nb5+ ions stabilizes the crystal phase at elevated temperatures up to 623 K. • Stable dielectric constant and high resistivity are achieved over a wide temperature range up to 573 K. [ABSTRACT FROM AUTHOR]

The nature of ferroelectric domain dynamics in polydomain epitaxial barium titanate thin film was investigated using the linear electro-optic effect. The dynamic response was studied as a function of bias field under pulsed excitation. Upon removal of the bias pulse a millisecond long transient response was observed that is attributed to 90° domain reversal. The dynamic response and its field dependence are described by the Kohlrausch–Williams–Watts stretched exponential function in time with an average relaxation time <τ>. This average time for polarization reversal is a function of applied electric field E and is given by <τ>=τ0 exp(α/E), where τ0 is the prefactor and α is the activation field. The measured activation fields depended on bias. Activation fields of 2.0 and 0.7 V/μm measured under high and low bias conditions are comparable to those observed for bulk barium titanate. [ABSTRACT FROM AUTHOR]

In this work, (Li, Nb) co-doped TiO 2 ceramics (LNTO x , x < 0.1), were synthesized through a conventional solid state reaction method. As revealed by X-ray diffraction (XRD) spectra, all LNTO ceramics exhibited pure tetragonal rutile structure. The LNTO 0.01 ceramic showed a colossal permittivity over 7000 and a low dielectric loss (tg δ < 0.06) in a wide frequency range of 102 Hz–107 Hz. The dielectric spectra under DC biases were tested at different temperatures. The experimental data could fit the modified Debye equation well. It was found that there are multiple dielectric polarization mechanisms in LNTO ceramics including space charge polarization, relaxor-type relaxation, polaron hopping and dipole polarization related with localized electrons. [ABSTRACT FROM AUTHOR]

Abstract Here we report the first spectroscopic alpha particle detection based on CsPbBr 3 detectors with asymmetric contacts. The CsPbBr 3 single crystal was grown from the melt using Bridgman method and then fabricated into detectors with different contacts. The In/CsPbBr 3 /Au detector presented a low dark current density (∼ 100 nA/cm2) and temporal stable performance under high electric field (1000 V/cm). Such detector demonstrated excellent gamma ray resolving capability with a full-width at half maximum (FWHM) of ∼ 5.9 keV for the 57Co 122 keV γ ray. The CsPbBr 3 detector was capable of simultaneously resolving both the alpha particle (5.5 MeV) and γ ray (59.5 keV) peaks from 241Am radioactive isotope. The transport properties of CsPbBr 3 were then determined based on the alpha particle spectra and corresponding rise time distributions. The equivalent values of electron and hole mobilities were indicated as 63 and 49 cm2/(V ⋅ s) respectively. The calculated electron and hole mobility-lifetime products were 4.5 × 10−4 and 9.5 × 10−4 cm2/V, respectively, demonstrating superior transport properties of holes over electrons in CsPbBr 3. This work widens the scope of perovskite detectors to encompass charged radiation as well as high energy X/ γ rays, and will significantly promote and guide further studies on perovskite materials for radiation detection applications. Highlights • The first α particle spectroscopy by CsPbBr 3 detectors was clearly demonstrated. • In/CsPbBr 3 /Au detector was fabricated and exhibited low and stable dark current. • In/CsPbBr 3 /Au detector resolved both α particle and γ ray peaks from 241Am isotope. • The nearly balanced e and h mobilities of CsPbBr 3 were 63 and 49 cm2/(V s), respectively. • The μ τ products for e and h were 4.5 × 10−4 and 9.5 × 10−4 cm2/V, respectively. [ABSTRACT FROM AUTHOR]

Abstract We report on the measurement of frequency dependent noise spectra of photoconductive ternary compounds Cs 3 Sb 2 I 9 , Rb 3 Sb 2 I 9 , Hg 3 Se 2 I 2 , and TlSn 2 I 5 for hard radiation detectors. The major sources of noise in these detectors are attributed to pickup noise, white noise, and frequency related 1/ f noise. At low frequencies, the noise spectral density function exhibited 1/ f α behavior where α is less than or equal to one. For those samples with α equal to one, radiation detection performances of the detectors, in terms of spectral measurements, have been reported in previous publications. The origin of 1/f noise of those samples is attributed to carrier fluctuations associated with deep centers/trapped holes. For those samples with α less than one, the origin of the deviation from a linear 1/f dependence is unknown and currently under investigation. However, this deviation is correlated with higher background white noise and lowered detector performance, and thus indicates that the material needs to be further optimized. Noise measurements are a useful indicator for screening prospective materials and samples for detectors. [ABSTRACT FROM AUTHOR]

Abstract Composites of Li-Al-B-Si-O (LABS) glass and β-Al 2 O 3 have been synthesized for low-temperature co-fired ceramics (LTCC) technology application. The main phase of sintered composites is Li 2 Al 2 Si 3 O 10 and β-Al 2 O 3 phase appears only when its content is higher than 35 wt%. The DC conductivities of sintered composites are all above 1 × 10−8 S/cm at the temperature of 473 K. The activation energies of alkali ions of different composites are all between the conductivity measured perpendicular and parallel to the c-axis of Eucryptite, which proves the ionic conductance of composites is associated with the main phase of Li 2 Al 2 Si 3 O 10. The CTE of the composites increased with the increase of β-Al 2 O 3. The CTE of 68 wt% LABS glass-32 wt% β-Al 2 O 3 is 3.15 ppm/°C (25–300 °C), which matches that of silicon (3.2 ppm/°C, 25–300 °C) well. The results indicate that the composites of Li-Al-B-Si-O glass and β-Al 2 O 3 can be a promising material for LTCC-silicon heterogeneous integration with anodic bonding technology. [ABSTRACT FROM AUTHOR]

Thermally stimulated depolarization current (TSDC) measurements were applied to investigate BaTiO3 single crystals with <100>, <110>, and <111> orientations, and annealed under different atmospheres, respectively. The TSDC peaks related to ferroelectric domain, ferroelectric–paraelectric phase transition, T i T i ′ − V Ö dipole relaxation and oxygen vacancy migration were observed from the TSDC spectra. The formation of oxygen vacancy clusters in BaTiO3 single crystals leads to a high dipole activation energy. The <111> crystalline face of BaTiO3 is more stable under external field than others. [ABSTRACT FROM AUTHOR]

The influence of CuO and B 2 O 3 addition on the sintering behavior, microstructure and microwave dielectric properties of Ti 1−x Cu x/3 Nb 2x/3 O 2 (TCN, x = 0.23) ceramic have been investigated. It was found that the addition of CuO and B 2 O 3 successfully reduced the sintering temperature of TCN ceramics from 950 to 875 °C. X-ray diffraction studies showed that addition of CuO-B 2 O 3 has no effect on the phase composition. The TCN ceramics with 0.5 wt% CuO-B 2 O 3 addition showed a high dielectric constant of 95.63, τ f value of + 329 ppm/°C and a good Q × f value of 8700 GHz after sintered at 875 °C for 5 h, cofirable with silver electrode. [ABSTRACT FROM AUTHOR]

Generally, the reduction of Eu 3+ to Eu 2+ in solids requires annealing in a reducing atmosphere. In this work, we find that the reduction of Eu 3+ to Eu 2+ can be realized in Yb 2 Si 2 O 7 phosphors after being soaked in boiling water. Eu 3+ -activated Yb 2 Si 2 O 7 with different doping concentrations was synthesized by a sol-gel method. The as-prepared Yb 2 Si 2 O 7 :Eu 3+ phosphors showed strong red emission at 612 nm under ultraviolet light, corresponding to the 5 D 0 → 7 F 2 transition of Eu 3+ . The optimized doping concentration of Eu 3+ was 7 mol% with the highest emission intensity at 612 nm. The valence change and luminescence properties of Eu-doped Yb 2 Si 2 O 7 phosphors after being soaked in boiling water are reported and the reduction mechanism from Eu 3+ to Eu 2+ in the compounds is discussed. Our findings suggest that this kind of Eu 3+ → Eu 2+ valence transfer might shed light on the development of phosphors for display applications. [ABSTRACT FROM AUTHOR]

In this study, undoped and Mn 2+ doped Ti 1−x Cu x/3 Nb 2x/3 O 2 (TCN, x = 0.2, 0.25, 0.3, 0.35) ceramics were prepared using a solid-state reaction method. The phase composition and microstructure of the TCN ceramics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicated that the density and permittivity of the TCN ceramics increase with the increasing of the Cu and Nb content. However, Q × f value of the undoped TCN ceramics decreases with an increase in the sintering temperature. A small amount of Mn 2+ doping has no effect on the permittivity, but improves the Q × f value. X-ray photoelectron spectroscopy (XPS) analysis indicated that the transition of Cu 2+ to Cu + during the sintering process could be inhibited by Mn 2+ doping, which suppresses the formation of oxygen vacancies, as a result, the improvement of Q × f value. Excellent microwave dielectric properties with a permittivity of 95 and Q × f value of 20800 GHz (@3.50 GHz) were achieved from the 0.6 at% Mn 2+ doped TCN (x = 0.25) ceramics sintered at 1025 °C for 5 h. [ABSTRACT FROM AUTHOR]

A parallel preparation method was developed using dry powders as starting materials to synthesize multi-compositional microwave dielectric ceramics. The Li 2 O-Nb 2 O 5 -TiO 2 ternary system was investigated as a model material. The validity of the parallel ceramic preparation process was confirmed by synthesizing a group of LiNb 0.6 Ti 0.5 O 3 ceramics in parallel, which showed the same crystalline structure and close dielectric properties. The ceramic libraries with M-phase-rich samples and Li 2 TiO 3 -rich samples were prepared using the parallel process, and the microwave dielectric properties and crystal phases were investigated systematically. An excellent microwave ceramic with a composition of 0.55Li 2 O-0.05Nb 2 O 5 -0.40TiO 2 was obtained, which has a dielectric constant of 18.4 and a high quality value ( Q × f ) of 79000 GHz. This parallel process can be applied extensively to explore a variety of bulk ceramic libraries for discovering new functional materials with high performances. [ABSTRACT FROM AUTHOR]

In this study, a colossal permittivity up to 3800 and a low dielectric loss of 0.11 at 1 kHz have been obtained from the (Li, In) co-doped ZnO ceramic [Zn (1−2x) (Li, In) x O] when x was 0.5%. Electric modulus spectroscopy and impedance analysis were used to investigate the origin of its high permittivity. Two relaxation peaks and a dielectric anomaly were observed in the temperature range of 293–363 K. According to the Debye relaxation theory, the low- and high-temperature relaxation peaks with activation energies of 0.09 eV and 0.29 eV, have been attributed to the hopping of singly and doubly charged oxygen vacancies, which are created by lithium and indium ions doping and oxygen deficiency during sintering process. After thermal treatment in an oxidizing atmosphere, the peaks related to the singly and doubly charged oxygen vacancies disappear and the permittivity reduces to ∼460 at room-temperature. From the X-ray photoelectron spectra (XPS), the concentrations of oxygen vacancies decrease after the O 2 -annealing process. The results reveal that the oxygen defects would be the main origin of the colossal permittivity of co-doped ZnO at room-temperature range. [ABSTRACT FROM AUTHOR]

Based on a novel green dielectric barrier discharge plasma induced chemical vapor generation (DBD plasma-CVG), an on-line hyphenation of high performance liquid chromatography (HPLC) with atomic fluorescence spectrometry (AFS) was developed for the speciation of inorganic mercury (Hg2+), methylmercury (MeHg) and ethylmercury (EtHg). Without the use of other chemical reagents, the decomposition of organic mercury species and the reduction of Hg2+ could be completed in one step with the DBD plasma-CVG system. The operating parameters of DBD plasma-CVG and HPLC were optimized. Separation of mercury species was accomplished in less than 14 min on a ZORBAX SB-C18 separation column with a mobile phase containing 0.01% (v/v) 2-mercaptoethanol, 10% (v/v) methanol and 0.06 mol L−1 NH4Ac at pH 6.8. The limits of detection of the method were found to be 1.6, 0.42 and 0.75 μg L−1 for Hg2+, MeHg and EtHg, respectively. The developed method was validated by determination of the main analytical figures of merit and applied to the analysis of the certified reference material GBW10029 (tuna fish). The on-line interfacing of HPLC with DBD plasma-CVG-AFS for the speciation of mercury is simple, environmentally friendly, and represents an attractive alternative to the conventional tetrahydroborate interface system. [ABSTRACT FROM AUTHOR]

Li 4 Ti 5 O 12 (LTO) were doped with the same group element (Zr4+), diagonal elements (Nb5+ and W6+), and same period element (V5+) of titanium, respectively, to quantitative doping effect and explore the possibility of diagonal line rule in doping. It is conducive to synthesis doping Li 4 Ti 5 O 12 with excellent properties by the ammonia-assisted mechanical ball-milling method (AAMBM). Through systematic experimental comparison, Li 4 Ti 4.95 Nb 0.05 O 12 (LTNO) exhibits finer particle, higher specific surface area, narrower band gap, and more excellent electrochemical performance compared to others, since Nb and Ti have similar ion polarization ability, standard electrode potential, and the conjugable outer electron arrangement (Nb 4d45s1 whose 5 s electrons can be delocalized to d orbits to form half full orbit state). Particularly, LTNO shows the highest initial first discharged capability up to 151 mAh g−1 and the capacity retention of 90% at 5 C rate after 300 cycles, indicating both outstanding high-rate discharge performance and cycling stability. The doping factor was proposed to roughly quantify their doping effect of Zr4+, Nb5+, V5+, and W6+, by using the ratio of specific capacity values of doped LTO and pure LTO after 500 cycles at 5 C, which are 1.2, 1.86, 1.05, and 1.08, respectively. [ABSTRACT FROM AUTHOR]

The silver diffusion behavior in the low-temperature cofired ceramic (LTCC) comprising of borosilicate glass and alumina was investigated in this work. Transmission electron microscope (TEM) analysis revealed that silver ions diffused into LTCC materials through the glass phase. The addition of copper oxide in the LTCC materials can suppress the silver diffusion during the sintering process because of the enhanced crystallization of borosilicate glass, which leads to the quick increase in glass viscosity and retards the silver diffusion. Thermal dynamic analysis confirmed that the diffusion coefficient of silver in the copper-oxide-modified LTCC materials was largely reduced. [ABSTRACT FROM AUTHOR]

The heavy metal selenophosphate, Pb2P2Se6, is a promising new material for cost-effective X-ray/γ-ray detection. Crystal boules of Pb2P2Se6 up to 25 mm in length and 15 mm in diameter are grown by a vertical Bridgman method. They are cut and processed into size-appropriate wafers for physical, photo-transport property studies, as well as γ-ray detector testing. The material is a semiconductor with an indirect bandgap of 1.88 eV and has electrical resistivity in the range of 1 × 1010 Ω cm. Pb2P2Se6 single crystal samples display a significant photoconductivity response to optical, X-ray, and γ-ray radiation. When tested with a 57Co γ-ray source, Pb2P2Se6 crystals show spectroscopic response and several generated pulse height spectra resolving the 122.1 and 136.5 keV 57Co radiation. The mobility-lifetime product of Pb2P2Se6 is estimated to be ≈3.5 × 10−5 cm2 V−1 for electron carriers. The Pb2P2Se6 compound melts congruently at 812 °C and has robust chemical/physical properties that promise low cost bulk production and detector development. [ABSTRACT FROM AUTHOR]

Mg and Mn co-doped LaGa0.7-xMgxMn0.3O3 (x = 0, 0.05, 0.10, 0.15) ceramics were prepared by a solid-state reaction method. The electrical properties of the LaGa0.7-xMgxMn0.3O3 ceramics were studied in detail by dielectric spectra, impedance spectra, and I-V characteristic analysis. Colossal permittivity up to 104 could be obtained across the frequency range up to 104 Hz. The impedance analysis of the co-doped LaGaO3 ceramics indicated that the Mott's variable range hopping (VRH) polarization should be the main origin of colossal permittivity. Mg and Mn co-doping suppressed the formation of Mn3+ and enhanced the VRH polarization, resulting in increased permittivity. Partial localization of electrons by Mg reduced the long-range electron hopping and led to the decrease in dielectric loss. [ABSTRACT FROM AUTHOR]

Colloidal photonic crystal (CPC) structure is an efficient candidate for light extraction from light-emitting diodes (LEDs). The preparation of a large area CPC structure on the light output surface of LEDs often involves sophisticated equipments such as nanoimprint lithography machine. In this study, we prepared a monolayer CaTiO3:Eu3+ red phosphors on the surface of three-dimensional photonic crystal, the extraction of photoluminescence (PL) can be enhanced compared to the extraction of PL in pristine phosphors. On the basis of theoretical analysis, enhancement is shown to be due to the photonic crystal effects. [ABSTRACT FROM PUBLISHER]

SrTiO3powders were synthesized by molten salt method with homemade different morphology TiO2in the eutectic NaCl-KCl salts. The phases, crystallite sizes, morphologies and band gap of the as-prepared products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV-Vis diffuse reflectance spectra respectively. The photocatalytic activity of SrTiO3with different morphology was measured by CO2reduction device. The morphologies of the as-synthesized SrTiO3depended on the morphologies of TiO2precursors, indicating that the formation process of SrTiO3in the molten salts was mainly controlled by the template formation mechanism. The results show that compared with different morphology SrTiO3, sphere-shaped SrTiO3exhibit best activity loaded 5%Cu, showed the least Eg and crystallite size. The photocatalytic activity has something to do with the crystallite and the Eg with different morphology. [ABSTRACT FROM PUBLISHER]

We analyzed low-temperature photoluminescence (PL) and the band edge excitonic emission in bulk halide perovskite CsPbCl 3 single crystals. Strong near band edge excitonic emission is observed at 420 nm and a series of excitonic states was observed. Temperature-dependent PL measurements on cesium lead chloride over a wide temperature range from 13 K to 295 K revealed significant electron phonon coupling with a Huang-Rhys parameter ranging from 1.34 to 3.38. A primary experimental finding is that the near band edge PL emission shows existence of multiple sharp features at low temperatures that are attributable to free excitons, bound excitons, and their phonon replicas. The PL also shows evidence of band tailing effects due to disorder. We investigated the recombination mechanism of photogenerated charge carriers by means of time-resolved PL (TR-PL) spectroscopy at low temperatures and various excitation powers and observed competing mono- and bimolecular recombination processes. A dynamic model is proposed to describe the TR-PL. We observed both long-lived and short-lived recombination where the short-lived time decay is attributed to free exciton recombination, whereas the long-lived decay to bound exciton recombination involving traps due to intrinsic disorder. • CsPbCl 3 single crystal samples are grown with the Bridgman method. • The exciton - LO phonon coupling becomes dominant for temperature above 120 K. • PL dependence on excitation power shows that the PL emission is excitonic in nature. [ABSTRACT FROM AUTHOR]

We report the synthesis, physicalcharacterization, and crystalgrowth of Tl4CdI6. We show that this materialhas good photoconductivity and is a promising semiconductor for roomtemperature X-ray and γ-ray detection. Large single crystalswere grown by the vertical Bridgman method and cut to dimensions appropriatefor detector testing. Single crystal X-ray diffraction refinementsconfirm that Tl4CdI6crystallizes in the tetragonalcrystal system with a centrosymmetric space group of P4/mnc, with a calculated density of 6.87 g/cm3. Thermal analysis and high-temperature synchrotron powderdiffraction studies were used to determine phase relationships andcrystallization behavior during crystal growth. We have elucidatedthe reason for different colors encountered when synthesizing or growingsingle crystals of Tl4CdI6(yellow, red, andblack), and it is the presence of a small amount of TlI impurity.We report proper crystal growth conditions to obtain essentially pureyellow Tl4CdI6crystals. The material havingthe yellow color has a band gap of 2.8 eV. First-principles densityfunctional theory calculations indicate a direct band gap at the Γpoint of the Brillouin zone. The Tl4CdI6crystalshave a resistivity of 1010Ω·cm. Photoconductivitymeasurements on the as-grown crystals show mobility-lifetime producton the order of 10–4cm2/V for both electronsand holes. The promising detector properties of this material areconfirmed by preliminary measurements showing a clear spectral responseto an Ag X-ray source, which classifies Tl4CdI6as an emerging material for radiation detection. [ABSTRACT FROM AUTHOR]

Abstract: M-phase Li–Ta–Ti–O (LTT) microsheets were synthesized by the molten salt method. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electron diffraction analyses were performed to analyze the morphology and microstructure of the LTT microsheets. The average number of layers of the LTT microsheets increases with increasing the synthesis temperature and holding time, and pure M-phase LTT microsheets are obtained at a temperature above 1000°C. Both terrace-ledge-kink and Ostwald ripening mechanisms are important for the formation of the M-phase LTT microsheets. We demonstrate that the size of LTT microsheets could be controlled by adjusting the synthesis temperature, holding time, and the weight ratio of the raw powders to LiCl salt. These LTT microsheets with tunable size are promising building blocks for high performance microwave ceramics. [Copyright &y& Elsevier]

Highlights: [•] The structural colored fiber was prepared by a magnetic field induced photopolymerization method. [•] Long-range one-dimensional superparamagnetic chains were formed in PEGDA resin. [•] The structural colors (blue, green, and red) were generated instantaneously in micro-space. [•] This process may have great potential for development in the actual fiber dyeing process. [ABSTRACT FROM AUTHOR]

Thermal performance of metallized low temperature co-fired ceramic (LTCC) composites was investigated in this paper. Seven metallized LTCC composites with different structures were designed and fabricated by traditional LTCC process. The thermal conductivity of the metallized LTCC composites with thermal vias was enhanced by inserting parallel silver layers within the composites. The thermal performance of high power LED package based on the metallized LTCC composite substrates was simulated by finite element analysis method. The results demonstrated that horizontal heat dissipation was very important except for vertical thermal vias in the LTCC substrate. [ABSTRACT FROM PUBLISHER]

Abstract: A new type of low temperature co-fired ceramic (LTCC) composite, comprising β-Si3N4 whiskers and calcium aluminosilicate (CAS) glass, is introduced in this paper. We show that the CAS–Si3N4 composite can be densified at 775–850°C in air. The effect of β-Si3N4 whiskers incorporation on the thermal conductivity of this relatively low-temperature sintered CAS–Si3N4 composite is investigated. The thermal conductivity of the CAS glass is increased from 1.6 to 7.9W/mK after adding 35vol% of β-Si3N4 whiskers. Microstructure characterization and percolation model analysis indicate that the likely cause of increased thermal conductivity of the ceramic composites is the formation of thermal percolation networks. The crystallization of the CAS glass also contributes to the enhancement of thermal conductivity. The sample with the highest thermal conductivity shows a low relative dielectric constant of 7.1 and a dielectric loss of 0.006 at 1MHz. Such a ceramic composite with excellent thermal and dielectric properties is a promising LTCC substrate material. [Copyright &y& Elsevier]

Abstract: The effects of β-Si3N4 whiskers on the thermal conductivity of low-temperature sintered borosilicate glass–AlN composites were systematically investigated. The thermal conductivity of borosilicate glass–AlN ceramic composite was increased from 11.9 to 18.8W/mK by incorporating 14vol% β-Si3N4 whiskers, and high flexural strength up to 226MPa were achieved along with low relative dielectric constant of 6.5 and dielectric loss of 0.16% at 1MHz. Microstructure characterization and percolation model analysis indicated that thermal percolation network formation in the ceramic composites led to the high thermal conductivity. The crystallization of the borosilicate microcrystal glass also contributed to the enhancement of thermal conductivity. Such ceramic composites with low sintering temperature and high thermal conductivity might be a promising material for electronic packaging applications. [Copyright &y& Elsevier]

Abstract: Pencil-like ZnO microrods was synthesized via a simple solvothermal process in an aqueous solution of ethylenediamine and ethanolamine. The as-prepared ZnO was characterized by X-ray powder diffraction, field-emission scanning electron microscopy, room temperature photoluminescence spectra and UV–vis absorption spectra. The results indicated that ZnO microrods had the length in the range of 1.3–25μm. The photocatalytic activity was studied by degradation of methylene blue (MB) aqueous solution, which showed that the as-prepared ZnO microrods possessed a high photocatalytic activity. The formation mechanism of the pencil-like ZnO was also investigated based on the experimental results. [Copyright &y& Elsevier]

Abstract: Nb2O5 nanorod array films were synthesized by a facile hydrothermal process using niobium metal foil and NH4F as precursors. The Nb2O5 nanorods stand on the niobium metal foil substrate and are less than 100nm in diameter and about 1μm in length. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) characterizations indicate that these nanorods have orthorhombic structure and grew longitudinally along 〈001〉 direction. The nanorod growth mechanism was discussed. Thermal annealing at a temperature below 500°C did not change the microstructure of nanorods but improve the crystallinity. The Nb2O5 nanorod array films have been tested as cathode material for lithium battery, which showed a good specific capacity up to 380mAhg−1 even after 50 charge/discharge cycles. [Copyright &y& Elsevier]

Abstract: Zn1−x Ni x O (x=0–0.25) hierarchical microspheres were synthesized via a solvothermal process in ethylene glycol. The magnetic microspheres were characterized by X-ray powder diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectra, X-ray photoelectron spectroscopy, room-temperature photoluminescence spectra, and vibrating sample magnetometer. The as-prepared samples take on a well-defined spherical architecture following the processes of spontaneous aggregation and localized Ostwald ripening. Dependence of the magnetization and morphology on Ni2+ content was observed. Magnetic hysteresis loops reveal that the Ni-doped ZnO microspheres exhibit ferromagnetic loops at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a cerium dioxide (CeO2) modified titanium dioxide (TiO2) nanotube array film was fabricated by electrodeposition of CeO2 nanoparticles onto an anodized TiO2 nanotube array. The structural investigation by X-ray diffraction, scanning electron microscopy and transmission electron microscopy indicated that the CeO2 nanoparticles grew uniformly on the walls of the TiO2 nanotubes. The composite was composed of cubic-phase CeO2 crystallites and anatase-phase TiO2 after annealing at 450°C. The cyclic voltammetry and chronoamperometric charge/discharge measurement results indicated that the CeO2 modification obviously increased the charge storage capacity of the TiO2 nanotubes. The charge transfer process at the surface, that is, the pseudocapacitance, was the dominate mechanism of the charge storage in CeO2-modified TiO2 nanotubes. The greater number of surface active sites resulting from uniform application of the CeO2 nanoparticles to the well-aligned TiO2 nanotubes contributed to the enhancement of the charge storage density. [Copyright &y& Elsevier]

Abstract: Tungsten oxide nanorods assembled microspheres were synthesized by a facile hydrothermal process at 180°C using ammonium metatungstate and oxalic acid as starting materials. The morphology and structural properties were investigated using scanning electron microscopy, powder X-ray diffraction, and transmission electron microscopy. The as-synthesized microspheres are composed of orthorhombic WO3·xH2O nanorods with diameter less than 100nm. These microspheres lose water gradually during annealing and transfer to monoclinic WO3 when annealed at 550°C. The gas sensing properties of the microspheres annealed at different temperatures were studied by exposing the gas sensors made from microspheres to NO2 gas. The results indicated that the crystalline phase of the microspheres has no obvious effect on the gas sensing performance. The microspheres annealed at 350°C showed fast and the highest response to NO2 gas due to the three-dimensional network based on the nanorods and the high effective surface area. [Copyright &y& Elsevier]

Abstract: A kind of ZnO:(La, Eu)Cl nanocomposite thin film phosphor with strong red emission was synthesized by the sol–gel process. X-ray diffraction and scanning electron microscopy characterization indicate that the films were composed of nano-sized grains and a LaOCl phase appeared accompanying with (100) oriented ZnO phase after annealed at 600 °C in oxygen. The photoluminescence properties were investigated by measuring the excitation and emission spectra. These luminescence results suggested that Eu3+ ions could incorporate into the LaOCl lattice and charge transfer occurred between LaOCl phase and Eu3+ ions. La co-doping with Eu-Cl leads to the improvement of the red luminescence of Eu3+ and also suppressed the broad green emission of ZnO host. [Copyright &y& Elsevier]

Abstract: Gallium oxide nanowires were synthesized by a chemical thermal evaporation method using gallium metal as a source material. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations indicate that the obtained nanowires are well-crystallized single phase monoclinic Ga2O3. Multiple nanowire gas sensors were fabricated by dispensing the Ga2O3 nanowires on an interdigitated Pt-electrode. The Ga2O3 nanowire gas sensors show reversible response to O2 and CO gases in a working temperature range of 100–500°C. A peak response is found at 300°C for O2 gas and the peak response appears at 200°C for CO gas. For both kinds of gases, the sensor response increases empirically with an increase of gas concentration. The results demonstrate the possibility of using the Ga2O3-based gas sensor at low working temperature field. [Copyright &y& Elsevier]

Abstract: The influences of thermal annealing on the microstructure and NO2-sensing properties of sputtered WO3 thin films were investigated. The WO3 films as-deposited at room temperature were amorphous and would crystallize to monoclinic structure when annealed at 350°C or above. The grains and pores in the WO3 films grew larger with an increase in annealing temperature. The effective surface area and pore volume changed non-monotonously with increasing the annealing temperature. The film annealed at 350°C showed the largest effective surface area. The film annealed at 500°C had the largest pore volume. Among the films investigated in this study, the WO3 thin film annealed at 500°C showed the quickest response/recovery and the highest response to 10ppm NO2. These results indicate the importance of achieving porous structure on improving the gas sensing performance. [Copyright &y& Elsevier]

Abstract: This paper presents a strategy for fabricating low loss waveguide devices based on high electro-optic (EO) coefficient self-assembled superlattice (SAS) films, a new sort of polymeric films grown on SiO2 film and coated with other polymeric films to form multi-layer EO waveguides structure without electric field poling. Firstly, the optical propagation loss induced by the absorption of electrodes is simulated and optimized to obtain both the low optical loss and the low drive voltage. Then this paper gives the scanned electron microscopic (SEM) images of the fabricated devices, the simulated and experimental images of the single guided mode, and the measured optical propagation loss of the EO waveguide devices of 1.0dB/cm. Finally, the very great agreement between the simulated and measured results of propagation loss of devices is observed. [Copyright &y& Elsevier]

Abstract: We simulate thin-film based electro-optic modulator structures to target low drive voltage, high-speed modulation, and small device size by using BaTiO3 ferroelectric film as an exemplary device material with optimizing film thickness. The calculations are performed for both the case of an experimental film having r eff =35pm/V and the case of an ideal thin-film having r 51 =730pm/V. For the case of r 51 =730pm/V, a new relation between the drive voltage and the interaction length is derived with respect to the special configuration of BaTiO3 thin-films. For the optimal case of the film thickness and the waveguide design, the frequency–voltage-size performances that can be achieved include: >2.5GHz with 0.75 V V π and 31.1mm length, 10GHz with 1.5 V V π and 7.8mm length, >40GHz with 3.0 V V π and 1.9mm length, and >100GHz with 4.8 V V π and 0.8mm length. Various physical factors unique to the frequency–voltage-size performance trade-off of the thin-film EO modulator structures are discussed. [Copyright &y& Elsevier]

Core-rim structure has distinct advantage to improve the performances of KNN-based piezoceramics. Whereas the state of the core-rim structure is difficult to control during sintering. Here, the core-rim structured 0.96(K 0.51 Na 0.47 Li 0.02)(Nb 0.8 Ta 0.2)O 3 -0.04CaZrO 3 (KNLNT) ceramics were both obtained by conventional sintering (CS) and rapid sintering (RS). KNLNT ceramics prepared by rapid sintering exhibit more outstanding controllability on grain growth and core-rim structure and can hold the core/rim size ratio in a stable and favorable level due to extended effective range of grain boundary diffusion in densification. Benefiting from the controllable microstructure, the RS method prepared samples show excellent performance. The unipolar strain value of RS-1240 (S max =0.252%) is 2.07 times as much as CS-1110 (S max =0.122%). Large strain, low hysteresis and low dielectric permittivity features make the core-rim structured KNLNT ceramics a potential material for pulse drive applications and demonstrate that the manual precise control of core-rim structure could create many possibilities on materials design. [Display omitted] [ABSTRACT FROM AUTHOR]

Bi‐Zn‐Nb‐O‐based microwave dielectric ceramics are promising candidates for wireless communication. Investigations have concentrated on their fabrication methods and doping modification. In this work, the densification mechanism and grain growth kinetics of the Bi‐Zn‐Nb‐O‐based microwave dielectric ceramics were explored. A significantly wide sintering temperature window (800–1000°C) of the monoclinic Bi2Zn2/3Nb4/3O7 (BZN) was found. High‐density stacking faults were observed in BZN grains at the initial stage of sintering, which could act as paths for mass transport, thus remarkably accelerating the densification process and decreasing the densification temperature. On the other hand, BZN possesses a high grain growth exponent and activation energy, which indicates a slow grain growth rate and a high threshold for abnormal grain growth, corresponding to the wide sintering temperature window. Moreover, the BZN ceramics display good microwave dielectric properties stability over a wide temperature range (25–450°C). [ABSTRACT FROM AUTHOR]

TeO2 single crystal has drawn much attention in recent years due to its excellent acousto‐optic (AO) performance in the field of spectral imaging and optical processing. The optical properties of TeO2 single crystal are critical for the fabrication of AO devices. To improve the optical properties of the TeO2 single crystal, Mn4+ ions were doped into the TeO2 lattice. Herein, bulk TeO2 single crystal and TeO2:0.02Mn4+ single crystal have been successfully grown by a Bridgman method. Compared with the TeO2 single crystal, a 30% transmittance increase was observed in the TeO2:0.02Mn4+ single crystal. Furthermore, the TeO2:0.02Mn4+ single crystal shows a smaller extinction coefficient (≤0.01) in the Vis–NIR region, indicating less optical loss. The bandgap energy of TeO2:0.02Mn4+ was broadened from 3.360 to 3.635 eV. In addition, TeO2:0.02Mn4+ single crystal exhibits a higher refractive index (about 2.244), which indicates that TeO2:0.02Mn4+ single crystal is a potential medium for high‐efficiency AO devices. [ABSTRACT FROM AUTHOR]

Abstract: The optical and charge transport properties of the thallous chalcogenide compound Tl6I4Se were characterized. The semiconductor crystals are grown by the modified Bridgman method. We have measured the refractive index, and absorption coefficient of the compound ranging from 300 to 1500nm by analysis of the UV–vis–near IR transmission and reflection spectra. The band gap is 1.8eV. For the evaluation of detector performance, the mobility-lifetime products for both the electron and hole carriers were measured. Tl6I4Se has mobility-lifetime products of 7.1×10−3 and 5.9×10−4 cm2/V for electron and hole carriers, respectively, which are comparable to those of Cd0.9Zn0.1Te. The γ-ray spectrum for a Tl6I4Se detector was measured. Its response to the 122keV of 57Co source is comparable to that of Cd0.9Zn0.1Te. [Copyright &y& Elsevier]

Nonlinear photonic crystal waveguide structures were fabricated from barium titanate thin films using nanolithography. A cascaded Bragg reflector using a strip waveguide was designed and analyzed. Both simulation and experimental results show that there is sufficient refractive index contrast to form a stop band by only etching through the Si3N4 strip layer. The band gap of the Bragg reflector can be engineered through control of the Bragg spacing, thickness, and etching depth of the strip layer. The transmission spectrum of the Bragg reflector waveguide was measured over the spectral range of 1500–1580 nm. A 27 nm wide stop band was obtained for a millimeter long sample. The nonlinear photonic crystal waveguides are potentially suitable as tunable filters, optical switches, and ultrawide bandwidth modulators. [ABSTRACT FROM AUTHOR]

Tellurium dioxide (TeO2) nanowires with a tetragonal structure have been grown by thermally evaporating tellurium metal at 400 °C in air. The nanowires produced have diameters ranging from 30 to 200 nm and have lengths of several tens of micrometers. Gas sensors were fabricated using the obtained TeO2 nanowires. The sensing behavior to NO2, NH3, and H2S gases at room temperature showed typical characteristics of a p-type semiconductor. The results demonstrate the potential to develop TeO2 nanowire based gas sensors with low power consumption. [ABSTRACT FROM AUTHOR]

The SrAl2O4:Eu2+ phosphor powders have been synthesized by sol–gel process. Electroluminescent (EL) properties of the SrAl2O4:Eu2+ phosphor were investigated using a convenient thick film device. Green light emitting at a peak of 508 nm was obtained when driven by sine alternating current (AC). The color coordinate of the emission was x=0.148 and y=0.635. Luminance–voltage and afterglow characteristics of the SrAl2O4:Eu2+ EL devices were studied. The results show that SrAl2O4:Eu2+ can be used as green phosphor for EL displays. [Copyright &y& Elsevier]