Lixi Wang

Synthesis and photoluminescence of Eu3+-activated double perovskite NaGdMg(W, Mo)O6 – a potential red phosphor for solid state lighting

A novel high-efficiency double perovskite NaGdMg(W, Mo)O6:Eu phosphor is obtained by an improved citrate–EDTA complexing method. An emission intensity over twenty times that of a commercial red phosphor is observed. The host material has high-efficiency absorption, high doping concentration for many rare earth ions and intense emission with different colors.

Microwave electromagnetic and absorbing properties of Dy3+ doped MnZn ferrites

Abstract Dy3+ doped Mn-Zn ferrites Mn0.3Zn0.7Fe2–xDyxO4x=0, 0.01, 0.02, 0.03, 0.04were prepared by the conventional solid-state reaction. The crystal structure, surface morphology and electromagnetic properties of the calcined samples were characterized by X-ray diffraction analysis(XRD), scanning electron microscopy(SEM) and network analyzer (Agilent 8722ET). All the XRD patterns showed the single phase of the spinel-type ferrite without other intermediate when x≤0.03. The average crystallite size was about 44–56 nm. The microwave electromagnetic properties of the samples were studied at the frequency range from 2 GHz to 18 GHz. It was shown that small amounts of Dy3+ substitution could adjust microwave electromagnetic parameters magically. The tan δ exhibited a maximal peak when x=0.03, and the peak value was 0.56. It indicated that the microwave electromagnetic loss properties were excellent when x=0.03. Furthermore, the reasons were also discussed using electromagnetic theory. The reflection loss (RL) increased with the Dy3+ content when x

Er3+-substituted W-type barium ferrite: preparation and electromagnetic properties

Abstract Er 3+ -substituted W-type barium ferrites Ba 1- x Er x (Zn 0.3 Co 0.7 ) 2 Fe 16 O 27 ( x =0.00, 0.05, 0.10, 0.15, 0.20) were synthesized by polymer adsorbent combustion method. Samples were characterized by X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and network analyzer to investigate the relationships among Er 3+ concentration, crystal structure, surface morphology and electromagnetic properties. All the XRD patterns showed pure phase of W-type barium ferrite when x =0.15, while the impurity phase of ErFeO 3 appeared when x =0.20. The pure W-type barium ferrite showed a hexagonal flake shape. In addition, the microwave electromagnetic properties of samples were analyzed in the frequency range of 2-18 GHz. It was indicated that the electromagnetic properties were significantly improved when Er 3+ doping content was 0.10. The reasons were also discussed using electromagnetic theory. The optimized ferrite exhibited excellent microwave absorption performance. The maximum of reflection loss (RL) reached about −27.4 dB and RL was below −10 dB at the frequency range from 8.4 GHz to 18 GHz, when the thickness was 2.6 mm.

Concentration dependence of luminescent properties for Sr 2 TiO 4 : Eu 3+ red phosphor and its charge compensation

Sr2TiO4:Eu3+ phosphors using M+ (M = Li+, Na+, and K+) as charge compensators were prepared by the solid-state reaction. The powders were investigated by powder X-ray diffraction (XRD) and photoluminescence spectra (PL) to study the phase composition, structure, and luminescent properties. The results showed that Li+ ion was the best charge compensator. The phase was Sr2TiO4 when the doping concentration was small (x ≤ 10.0%). When x reached 15.0%, the phase turned into Sr3Ti3O7 because of the structure damage. The phosphor could be effectively excited by ultraviolet (365, 395 nm) and blue light (465 nm), and thenit emitted intense red light that peaked at around 620nm (5D0 → 7F2). In addition, the emission of 700nm (5D0 → 7F4) enhanced the red light color purity. The CIE chromaticity coordinates of samples with the higher red emission were between (0.650, 0.344) and (0.635, 0.352). Doped layered titanate Sr2TiO4:Eu3+ is a promising candidate red phosphor for white LEDs which can be suited for both near-UV LED chip and blue LED chip.

Effective red compensation of Sr 2 SiO 4 : Dy 3+ phosphor by codoping Mn 2+ ions and its energy transfer

Mn2+ ions codoped Sr2SiO4 : Dy3+ phosphors were prepared by the solid-state reaction method using NH4Cl as the flux. Their phase compositions, photoluminescence properties, and the energy transfer process were systematically investigated. All Mn/Dy codoped powders were α′-Sr2SiO4. The codoping concentration range of Mn2+ was ≤ 4.0mol% to keep the structure undamaged. The broad red emission of Mn2+ centered at 647nm in Sr2SiO4 :Mn, Dy powders, which effectively compensated the red emission of Sr2SiO4 : Dy3+ phosphor. The CIE chromaticity coordinates dramatically changed from (0.310, 0.340) to (0.332, 0.326) due to the red enhancement via the energy transfer from Dy3+ to Mn2+. This energy transfer is realized by the exchange interaction. But the luminescence quenching of Sr2SiO4 :Dy, Mn phosphor was mainly caused by the electric multipoles interaction. The concentration optimized (Sr0.96, Mn0.02, Dy0.02)2SiO4 phosphor with high and almost pure white emission has great potential to act as a single-matrix white phosphor for white LEDs.

Microwave dielectric properties of high-Q Mg(SnxTi1−x)O3 ceramics

A series of Sn-doped Mg(SnxTi1−x)O3 ceramics were prepared using the conventional solid-state route. The influence of Sn4+ substitution for Ti4+ on the microstructure and microwave dielectric properties of Mg(SnxTi1−x)O3 ceramics was systematically investigated. Substitution with a suitable amount of Sn can eliminate the MgTi2O5 phase. The dielectric constants and temperature coefficients of resonant frequency changed slightly with the variation in Sn content in the specimens. However, the quality factors (Q) dramatically improved and were sensitive to the concentration of Sn4+. The high Q value was attributed to the uniform grain, clean and narrow grain boundary, and elimination of the MgTi2O5 phase. Moreover, the composition-optimized Mg(Sn0.05Ti0.95)O3 ceramics sintered at 1390°C exhibited excellent microwave dielectric properties of ɛr = 17.61, Q×f = 328,543 GHz, and τf = −42 ppm/°C.

Synthesis and co-luminescence properties of Tb3+-methacrylic acid-1,10-phenanthroline complexes doped with Eu3+

A series of rare earth complexes Tb1−xEux(MAA)3phen (x=0.00, 0.01, 0.03, 0.05, 0.07, 0.09, 0.10, 0.30, and 0.50) were synthesized with MAA as the first ligand and phen as the second ligand. The complexes were characterized by means of FT-IR, thermogravimetry-differential scanning calorimetry (TG-DSC), XRD, UV absorption spectra, and photoluminescence spectra (PL). The results show that the luminescence intensity of Eu3+ increases as Tb3+ transfer the absorbed energy to Eu3+ in the complexes. The emission of Tb3+ at 545 nm is observed and increasing with x decreasing. When x=0.01, the luminescence intensity reaches the maximum value, and the emission intensity of Tb3+ at 545 nm and Eu3+ at 614 nm are almost equal. It realizes the co-luminescence of Eu3+ and Tb3+. We can obtain complexes with different colors by adjusting the ratio of Eu3+ to Tb3+.

Preparation and properties of Nd:YAG ultra-fine powders

Abstract Ultra-fine Nd:YAG powders with different doping concentrations were synthesized by sol-gel combustion method. The pure Nd:YAG could be prepared at the low temperature of 900 °C. Ethanol could improve the dispersity of powders, and the average size of the ultra-fine powders was around 250 nm. The reflection spectrum showed that there were several apparent characteristic absorption peaks and the intensity of these peaks enhanced with the increasing concentration of Nd 3+ . The luminescence spectrum, which was excited by 808 nm wavelength, exhibited several obvious emission bands in the range of 900-1150 nm. The emission intensity of Nd:YAG powders increased until the Nd content was above 3 mol.% due to the fluorescent quenching effect.

Optical property of SmAlO3 applied as 1.06 μm laser absorbing material

Abstract SmAlO 3 powders were successfully synthesized through the citrate sol-gel combustion method. The phase evolution of the prepared powders were characterized using thermal gravimetric (TG) analysis, differential scanning calorimetry (DSC) analysis and Fourier transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) was applied to examine the purity of the powders. The reflective properties of SmAlO 3 with changing temperatures were investigated by ultraviolet-visible near-infrared spectrophotometer (UVPC) specular reflection spectrum. The results displayed that pure SmAlO 3 phase with preferable reflectivity at 1.06 μm could be obtained at 900 °C for 2 h. Furthermore, the reflectivity of SmAlO 3 at various temperatures from −40 to 500 °C transformed within ±0.1%, and all maintained below 1% at 1.06 μm. The absorbance of SmAlO 3 in the resin solution was 2.134 and the moral absorption coefficient was about 384.8 in the work. The study indicated that SmAlO 3 powders may be a promising kind of heat resistant absorbing material for 1.06 μm laser defense, which could be further applied to laser absorbing coatings with a wide range of temperatures.

Investigation on the amounts of Na2CO3 and sulphur to obtain pure Y2O2S and up-conversion luminescence of Y2O2S:Er

The process to prepare pure phase of hexagonal Y2O2S was investigated. Effect of mixed flux of Na2CO3 and S amounts was studied. The phase composition and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the single phase of Y2O2S with smooth morphology could not be obtained as the molar ratio of Y2O3, Na2CO3 and S was in the range of 1:(0.5–1):(2–3) until the molar ratio was increased to 1:1.5:4. Different Er3+ concentration doped Y2O2S:Er powders were prepared with molar ratio of the raw materials 1:1.5:4. The quenching concentration of Er3+ in Y2O2S was more than 2 mol.%, which was due to the interaction of electric quadrupoles between Er3+ ions.