Intense Luminescence and Good Thermal Stability in a Mn2+-Activated Mg-Based Phosphor with Self-Reduction.

White light-emitting diodes provide widespread applications in lighting, electronic equipment, and high-tech displays. However, thermal quenching effect severely limits their practical application. Here, we developed an orange-red phosphor ß-KMg(PO3)3:Mn2+, which emits bright orange-red light when excited by ultraviolet light without the energy transfer of sensitizer, owing to the strong crystal field provided by ß-KMg(PO3)3 for Mn2+. The self-reduction of Mn4+ → Mn2+ and good thermal stability have been realized in an ambient atmosphere. The defect types were verified by X-ray photoelectron spectroscopy, and cationic vacancy plays a significant role in the self-reduction of Mn4+ → Mn2+. Furthermore, the properties of the trap energy levels were studied by thermoluminescence. The recombination luminescence of the detrapped carriers released from the deep trap levels at high temperatures suppresses the luminescence loss of thermal quenching. Moreover, the trap energy levels play an important role in the mechanoluminescence of ß-KMg(PO3)3:Mn2+. This work emphasizes the significance of the defects in the luminescent characteristics and opens up a new approach for the development of advanced optical functional materials.

Matching and adjusting energy band structures of Pd-modified sulphides (ZnS, In2S3 and CuS) and improving the photocatalytic activity of CO2 photoreduction.

A series of Pd-modified sulphide photocatalysts (ZnS-PdX%, In2S3-PdX% and CuS-PdX%) for the photoreduction of CO2 were synthesised via a simple hydrothermal method. Here, the introduction of the -S-Pd-S- surface species onto the surface of the sulphides extended the visible light absorption, prolonged the lifetime of photogenerated electrons and suppressed the recombination of the photocarriers. Additionally, the match between the band structure and the redox potential for the photoreduction of CO2 was improved. As a result, the photocatalytic activity of ZnS-Pd1.5%, In2S3-Pd1.5% and CuS-Pd1.5% was enhanced when compared with the results from ZnS, In2S3 and CuS photocatalysts. Also, ZnS-Pd1.5%, In2S3-Pd1.5% and CuS-Pd1.5% showed different photocatalytic activities due to differences in the matching relationships between the band structure and the redox potential. In this paper, extensive details on adjusting and matching the energy band structures, as well as viable methods for improving photocatalytic performance, are provided.

Preparation and Characterization of Microencapsulated Ethylenediamine with Epoxy Resin for Self-healing Composites.

Healing agent microcapsules have been used to realize self-healing for polymeric composites. In this work a novel kind of microcapsules encapsulating ethylenediamine (EDA) with epoxy resin as shell material were prepared by interfacial polymerization technology. The oil phase was epoxy resin prepolymer and carbon tetrachloride, and the water phase was EDA and deionized water. Under the action of emulsifier, a stable water-in-oil emulsion was formed. Then the emulsion was added to dimethyl silicone oil, stirred and dispersed, to prepare microcapsules. In addition, the factors affecting the preparation of microcapsules were studied. In this study, Fourier transform infrared(FTIR) was carried out to demonstrate the chemical structure of ethylenediamine microcapsules. Optical microscope(OM) and scanning electron microscope(SEM) were used to observe the morphology of microcapsules. Thermogravimetric analysis and differential scanning calorimetry were done to investigate the thermal properties of microcapsules. Permeability experiment and isothermal aging test were executed to verify the environment resistance of microcapsules. Results showed that EDA was successfully coated in epoxy resin and the microcapsule size was in the range of 50~630 µm. The synthesized microcapsules were thermally stable below 75 °C and perfect permeability resistance to ethanol solvent.

Synthesis, structure and characterization of M(IO3)2(HIO3) (M = Ca, Sr) as new anhydrous alkaline earth metal bis-iodate hydrogeniodate compounds.

Two new metal iodates, namely, M(IO3)2(HIO3) (M = Ca, Sr), were successfully synthesized by the hydrothermal method, and their structures were determined by single-crystal X-ray diffraction. They were found to be isostructural, and crystallized in the monoclinic space group P21/n with the lattice parameters: a = 6.9647(14) Å, b = 15.719(3) Å, c = 7.2042(14) Å, ß = 92.76(3)°, Z = 4 for Ca(IO3)2(HIO3), and a = 7.0697(14) Å, b = 15.986(3) Å, c = 7.3802(15) Å, ß = 93.13(3)°, Z = 4 for Sr(IO3)2(HIO3). The structure featured a [HIO3]·[IO3]- complex with strong intermolecular interactions, and it was composed of [IO3]- anions and [HIO3]·[IO3]- complexes interconnected by Ca2+ or Sr2+ cations. The two compounds were characterized by X-ray diffraction, IR and Raman spectroscopies, UV-Vis diffuse reflectance spectroscopy, thermogravimetry and differential scanning calorimetry as well as by theoretical calculations.

Crystal growth and optical characteristics of beryllium-free polyphosphate, KLa(PO3)4, a possible deep-ultraviolet nonlinear optical crystal.

Deep-ultraviolet nonlinear optical crystals are of great importance as key materials in generating coherent light with wavelength below 200 nm through cascaded frequency conversion of solid-state lasers. However, the solely usable crystal in practice, KBe2BO3F2 (KBBF), is still commercially unavailable because of the high toxicity of beryllium-containing and the extreme difficulty of crystal growth. Here, we report the crystal growth and characteristics of an beryllium-free polyphosphate, KLa(PO3)4. Centimeter-sized single crystals have been easily obtained by the flux method and slow-cooling technique. The second-harmonic generation efficiency of KLa(PO3)4 powder is 0.7 times that of KH2PO4; moreover, the KLa(PO3)4 crystal is phase-matchable. Remarkably, the KLa(PO3)4 crystal exhibits an absorption edge of 162 nm, which is the shortest among phase-matchable phosphates so far. These attributes make KLa(PO3)4 a possible deep-ultraviolet nonlinear optical crystal. An analysis of the dipole moments of the polyhedra and theoretical calculations by density functional theory were made to elucidate the structure-properties relationships of KLa(PO3)4.

Growth, structure, thermal properties and spectroscopic characteristics of Nd3+-doped KGdP4O12 crystal.

A single crystal of Nd3+-doped KGdP4O12 was successfully grown with the top-seeded solution growth and slow cooling (TSSG-SC) technique. It crystallizes in space group C2/c with cell parameters a = 7.812(2) Å, b = 12.307(3) Å, c = 10.474(2) Å, ß = 110.84(3)° and Z = 4. The IR and Raman spectra also indicated that the phosphoric polyhedra of Nd:KGdP4O12 has a cyclic symmetry. The chemical composition of the crystal was analyzed and the distribution coefficient of Nd3+ was calculated. The crystal morphology of KGdP4O12 was identified using X-ray diffraction. The compound has good thermal stability to 920°C. Its specific heat and thermal conductivity were determined for potential applications. The spectral properties of Nd:KGdP4O12 indicates that it exhibits broad absorption and emission bands, which are attributed to low symmetry of the crystal. The broad absorption band around 798 nm has a full-width at half-maximum (FWHM) of 14.8 nm and is suitable for AlGaAs laser diode pumping. Moreover, 5 at% Nd3+-doped KGdP4O12 crystal has a long luminescence lifetime of 300 µs and a high quantum efficiency of 96%.

Bending the ferroelectric domain wall by a bubble.

The shape of the ferroelectric domain wall mainly depends on the lattice structure and the pinning effect of random defects, but can we control it intentionally? Here we present a method to bend the domain wall by a bubble. A submillimeter bubble was put underneath a lithium niobate wafer inside a deionized water electrode to resist the propagation of the domain wall, and make the straight wall bend at an angle of 52°. The perpendicular surface screening field was considered to directly relate to the bending angle and the motion of the surface charged droplets in the bubble, and the detachment of droplets determined the bending of the domain wall. Further experiments succeeded in varying the bending angle from 52° to 0° by changing the ion concentration of the liquid electrode.

Highly efficient downconversion white light in Tm³âº/Tb³âº/Mn²âº tridoped P2O5-Li2O-Sb2O3 glass.

Tm³âº/Tb³âº/Mn²âº tridoped phosphate glasses containing different Mn²âº ion concentrations were synthesized to explore new white-light-emitting material. Under 355 nm excitation, the CIE coordinates (x=0.328, y=0.337) of the Mn0.10 sample doped with 0.10 wt. % Mn²âº are close to the standard equal energy white-light illumination (x=0.333, y=0.333). The quantum efficiency of the Mn0.01 sample is very high (~72.32%). The concentration of Mn²âº ions has a great effect on the emission color, and the energy transitions from Tm³âº, Tb³âº to Mn²âº become more intense with an increase in Mn2+ ion concentrations. The phenomenon is reasonably interpreted based on the analysis of the luminescence lifetime.

A non-linear optical crystal, Cd(3)Zn(3)(BO(3))(4).

The title compound, tricadmium trizinc tetraborate, Cd(3)Zn(3)(BO(3))(4), is a new non-linear optical (NLO) crystal and its structure has been determined by single-crystal X-ray diffraction. This compound is composed of planar [BO(3)](3-) groups sharing O atoms with CdO(4) or ZnO(4) tetrahedra. The BO(3) triangles are located on threefold axes and are arranged with nearly the same orientation. The Cd and Zn atoms are disordered on the same site in the proportion 1:1. A strong second harmonic generation of Nd:YAG laser radiation (lambda = 1064 nm) has been observed for a crystal of the title compound.