[en] Eu²⁺-doped SrAl₂O₄ phosphors were synthesized using a solid-state reaction method. The structural and the luminescent properties of the phosphors were investigated by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) excitation and emission spectra. SrAl₂O₄:Eu²⁺ phosphors with H₃BO₃ showed a pure monoclinic phase and exhibited a broad green-emission band with a maximum at 520 nm. The luminescence of the phosphors originates from the transition of Eu²⁺ ions from the 4f⁶5d¹ excited state to the 4f⁷ ground state. These results indicate that SrAl₂O₄:Eu²⁺ phosphors exhibit potential applications as efficient green emitting phosphors for use in near-ultraviolet light-emitting diodes.

[en] Pyroelectric measurements were carried out by the charge integration method in the temperature range from 100 K to 600 K for congruent and doped LiNbO₃ single crystals grown by the Czochralski method. The doped impurities were the transition metals Fe and Cr and rare earths Gd and Sm. The measured spontaneous polarization value of congruent LiNbO₃ was found to be about -2.6x10^-6 C/cm² in this temperature range, and the pyroelectric coefficient was about -6.5x10^-9 C/cm²K at room temperature and 2.5x10^-9 C/cm²K at 130 K. In the variation of the pyroelectric coefficient with increasing temperature, a strange anomaly was observed at about 360 K in both the congruent and the doped LiNbO₃ . The annealing effect in an air atmosphere was apparently revealed, but no evidence of the doping effect in the doped crystals was seen in these measurements. (Author)

[en] Highly crystallized CuPc/PbTe multilayer are prepared at substrate temperature from room temperature to 300 .deg. C by pulsed laser deposition and thermal evaporation method. From the measurement of AFM image, these all film exhibits composed of round grains and flat matrix. For observation the interface effect of multilayer, we measured the transverse current-voltage characteristics in the dark and under illumination. The photocarrier is generated in the CuPc layer and the electron-hole pairs are separated by the steep incline of the potential near the CuPc/PbTe interface. The CuPc/PbTe multilayers in the in-plane current-voltage curve exhibit larger photoconduction effect than that of CuPc single layer

[en] The high-temperature phenomena exhibited by KH₂PO₄ and RbH₂PO₄ have been investigated by differential thermal analysis, thermogravimetric methods, and thermo-polarizing microscopy. The thermal transformations which appear at T_p=196 deg. C in KH₂PO₄ and T_p=96 deg. C in RbH₂PO₄ are endothermic in addition to showing weight loss. On heating further to beyond T_p, the thermal transformation shows several endothermic peaks and there is weight loss in KH₂PO₄ and RbH₂PO₄. It has been observed by thermo-polarizing microscopy that until T_p is exceeded, uniaxial interference figures are exhibited by crystals of KH₂PO₄ and RbH₂PO₄, with cracks and chemical change at the surface of KH₂PO₄ near Tp ∼ 192 deg. C and RbH₂PO₄ near Tp ∼ 92 deg. C. The high-temperature phenomena exhibited by KH₂PO₄ and RbH₂PO₄ near Tp could indicate not changes from tetragonal to monoclinic structure but chemical decomposition at the surface of the crystals such as that described by nMH₂PO₄→M_nH₂P_nO_3n+1+(n-1)H₂O(M=K,Rb). (author)

[en] We explore the new systems of BiFeO_3^-Na_0.5Bi_4.5Ti₄O₁₅ (NaBFT) and BiFeO_3^-K_0.5Bi_4.5Ti₄O₁₅ (KBFT) solid solutions, with our interest being focused on the ferroelectric properties. The NaBFT and the KBFT thin films were prepared by using a chemical solution deposition method. The crystal structure and the surface morphology of the thin films were characterized by means of X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The values of the remnant polarization (2P_r) were 76.5 and 70.9 μC/cm² at an electric field of 663 kV/cm for the NaBFT and the KBFT thin films, respectively. The values of the dielectric constant were 748 and 717 at a frequency of 1 kHz for the NaBFT and the KBFT thin films, respectively. The values of the leakage current density of the KBFT and the NaBFT thin films were 6.9 x 10^-7 and 5.9 x 10^-6 A/cm² at an electric field of 100 kV/cm, respectively. Both thin films showed no polarization fatigue up to 1.4 x 10¹⁰ switching cycles. The good ferroelectric properties observed in the thin films may be related to reductions in the numbers of bismuth vacancies and oxygen vacancies.

[en] Single-phased [(1 − x) NBTxBMO, x = 0.01 (NBTBM1), (1 − x) NBTxBMO, x = 0.02 (NBTBM2), (1 − x) NBTxBMO, x = 0.03 (NBTBM3), and (1 − x) NBTxBMO, x = 0.04 (NBTBM4)] ceramic samples were prepared by using a solid-state method. X-ray diffraction analysis of the (1−x) NBTxBMO sample showed a rhombohedral structure and space group of R3c symmetry and confirmed the Rietveld refinement of the X-ray diffraction data. The micro-strain and the crystal sizes were calculated by using Williamson-Hall plots and experimentally verified with microstructural analyses. The in band-gap energy Eg varied from 3.28 to 3.17 eV for the (1− x) NBTxBMO ceramic samples. Furthermore, Raman spectra measured in the range from 100 to 1000 nm for the NBT-BMO powder samples showed new phonon modes and shifts to lower frequencies, which may be attributed to the incorporation of BMO into the NBT lattice.

[en] The effects of crystal structure on the ferroelectric properties of K_0.5Bi_4.5Ti₄O₁₅ (KBTi) thin films were investigated. Randomly-oriented and c-axis-oriented KBTi thin films were prepared by using a chemical solution deposition method. Both thin films were annealed at 750 .deg. C under an oxygen atmosphere. The randomly-oriented thin film showed better ferroelectric properties than the c-axis-oriented film. The remnant polarization (2P_r) of the randomly-oriented thin film was 13.5 μC/cm² at an applied electric field of 233 kV/cm, which is larger than that of the c-axis-oriented thin film, 4.8 μC/cm². This indicates that the polarization vector is not along the c-axis. The randomly-oriented thin film also showed a lower leakage current density than the c-axis-oriented thin film, as well as good fatigue endurance.

[en] Highlights: • Core-shell colloidal GdVO₄:Eu³⁺@SiO₂ nanocrystals were fabricated. • Intense red emission from these nanocrystals could be selectively quenched by Cu²⁺. • The limit of detection for Cu²⁺ is as low as 80 nM in aqueous solution. • The detection ability is highly reversible by the addition of EDTA. • The luminescence quenching and recovery processes can be repeated. Nowadays, in view of health and safety demands, the controlled design of selective and sensitive sensors for Cu²⁺ detection is of considerable importance. Therefore, we construct herein core-shell colloidal GdVO₄:Eu³⁺@SiO₂ nanocrystals (NCs) as optical sensor for the detection of Cu²⁺, which were synthesized by a facile hydrothermal reaction and encapsulated with a uniform layer of ultrathin silica through a sol-gel strategy. The NCs present strong red emission due to energy transfer from VO₄³⁻ groups to Eu³⁺ when exciting with ultraviolet (UV) light. This intense red emission from Eu³⁺ could be selectively quenched in the presence of Cu²⁺ in comparison to other metal ions and the limit of detection is as low as 80 nM in aqueous solution. It is revealed that the spectral overlap between the emission band of NCs and the absorption of Cu²⁺ accounts for this intriguing luminescence behavior. The detection ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA) with the recovery of almost 100% of the original luminescence. The luminescence quenching and recovery processes can be performed repeatedly with good sensing ability. These remarkable performances allow the colloidal GdVO₄:Eu³⁺@SiO₂ NCs a promising fluorescence chemosensor for detecting Cu²⁺ ions in aqueous solution.

[en] By applying the sol-gel method, we fabricated Ba1−xEuxTiO3 (BET) ceramics as a single peroveskite phase in the composition range of x = 0 ∼ 0.20. The BET ceramics displayed a ferroelectric phase transition temperature that changed from 120 ◦C to 80 ◦C, and exhibited the coexistance of the tetragonal, and cubic structures as the Eu composition was increased. They also displayed anomalous dielectric behaviors related to structural relaxation in the temperature range from 200 ◦C to 600 ◦C. We considered the Arrhenius temperature dependence of the dielectric relaxation time by using the electric modulus formalism. The characteristic activation energy was thought to be related with the substitution of Eu (Eu2+, Eu3+) ions for Ba2+ or Ti4+ ions in the perovskite structure.

[en] Highlights: • The wide range of the emission spectra of Sr₈MgLa(PO₄)₇: Eu²⁺_0.03 were clarified by Van Uitert equation and the crystal field strength equation. • The Mn²⁺ and Tb³⁺ had enhanced the total PL intensity up to 30% comparing to only Eu²⁺ doped phosphor. • W-LEDs using Sr₈MgLa(PO₄)₇: Eu²⁺_0.03, Mn²⁺_0.06, Tb³⁺_0.06 and BAM: Eu²⁺ resulted in an excellent CRI of 89 and CIE coordinates of (0.3463, 0.3898). - Abstract: A series of single phased phosphors Sr₈MgLa(PO₄)₇: Eu²⁺, Mn²⁺, Tb³⁺ were synthesized by solid state reaction methods for applications of white light emitting diodes(w-LEDs). The broad absorption band at the near ultraviolet (NUV) region of 250–450 nm was obtained, which is ascribed to the 4f⁷→ 4f⁶5d¹ electronic transition of the Eu²⁺ ions. Under NUV excitation, the broad yellow emission was obtained from tri-activated Sr₈MgLa(PO₄)₇ phosphors via combining three emission bands centered at 500, 550, and 600 nm contributed by Eu²⁺, Tb³⁺ and Mn²⁺, respectively. The optimized concentrations of Mn²⁺ and Tb³⁺ were 6 mol%, respectively, which enhanced the total PL intensity up to 30% comparing to only Eu²⁺ doped phosphor. Moreover, the quantum efficiency of Sr₈MgLa(PO₄)₇: Eu²⁺, Mn²⁺, Tb³⁺ phosphor had achieved up to 52%. The combination of a NUV chip with compound of Sr₈MgLa(PO₄)₇: Eu²⁺, Mn²⁺, Tb³⁺ and BaMgAl₁₀O₁₇:Eu²⁺ achieved tunable w-LEDs with high CRI. The results suggest that this single phased Sr₈MgLa(PO₄)₇: Eu²⁺, Mn²⁺, Tb³⁺ phosphor can be a key for the phosphor converted w-LEDs for warm white light emission.