Qitu Zhang

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

Citrate sol-gel combustion preparation and photoluminescence properties of YAG:Ce phosphors

Abstract Yellow-emitting YAG:Ce 3+ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions (MRCM), pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 °C. The phosphors exhibited the characteristic broadband visible luminescence of YAG:Ce. The optimum concentration of Ce 3+ was 1.0 mol.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole (d-q). Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower temperature. The Y 3 Al 5 O 12 :Ce 0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG:Ce.

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.

Fast synthesize ZnO quantum dots via ultrasonic method

Green emission ZnO quantum dots were synthesized by an ultrasonic sol-gel method. The ZnO quantum dots were synthesized in various ultrasonic temperature and time. Photoluminescence properties of these ZnO quantum dots were measured. Time-resolved photoluminescence decay spectra were also taken to discover the change of defects amount during the reaction. Both ultrasonic temperature and time could affect the type and amount of defects in ZnO quantum dots. Total defects of ZnO quantum dots decreased with the increasing of ultrasonic temperature and time. The dangling bonds defects disappeared faster than the optical defects. Types of optical defects first changed from oxygen interstitial defects to oxygen vacancy and zinc interstitial defects. Then transformed back to oxygen interstitial defects again. The sizes of ZnO quantum dots would be controlled by both ultrasonic temperature and time as well. That is, with the increasing of ultrasonic temperature and time, the sizes of ZnO quantum dots first decreased then increased. Moreover, concentrated raw materials solution brought larger sizes and more optical defects of ZnO quantum dots.

NMR Study on Structural Characteristics of Rare Earth Doped Boro-Alumino-Silicate Glasses

Abstract The structural characteristics of Re 2 O 3 doped B 2 O 3 -Al 2 O 3 -SiO 2 glasses and factors such as the component and heat-treating conditions affecting the glass structure were investigated by magic angle spin nuclear magnetic resonance (MAS NMR) spectroscopy and differential thermal analysis (DTA). It is found that, in B 2 O 3 -Al 2 O 3 -SiO 2 glass, the boron coordination sites are mainly of trigonal (B(3)) and tetrahedral (B(4)), and the aluminum coordination sites are Al(4), Al(5) and partly of Al(6). With the increase of BaO content in the B 2 O 3 -Al 2 O 3 -SiO 2 glass, B(3) gradually changes to B (4), and Al(5), Al(6) changes to Al(4). On the other hand, compared with Ba 2+ , RE 3+ can accumulate the boron network because of its higher field strength, which results in a large network structure. With the increase of samarium oxide, the silicate coordination Q 4 (3T) will have predominance gradually. Heat-treatment has little effect on the boron and aluminum coordination sites in the glass structure.

Effects of rare earth oxides on dielectric properties of Y2Ti2O7 series ceramics

Abstract A series of Y2Ti2O7 microwave dielectric ceramics were synthesized by conventional solid-state method. The effects of rare earth oxide (La2O3, CeO2, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Dy2O3) and Nd2O3 doping content on the microstructure and dielectric properties of Y2Ti2O7 ceramics were investigated. The experimental results showed that the rare earth ions were considered to dissolve in Y-sites of the pyrochlore structure, different rare earth oxides and concentration had different influences on Y2Ti2O7 ceramics. It was found that the rare earth oxide could decrease dielectric loss obviously, and the tf could be adjusted to zero with proper concentration. The Y2Ti2O7 ceramics with 1 mol.% neodymium oxide(Nd2O3) added showed optimum comprehensive properties, with the sintering temperature 1450 °C, the permittivity 45, the value of Q·f 22000 GHz, and the tf value 179 ppm/°C, while 1 mol.% Nd oxide (Nd2O3) was added.

Preparation and properties of nanocrystal SmBO3 by nitrate-citrate sol-gel combustion method

Abstract Nanocrystal SmBO3 powders were synthesized by nitrate-citrate sol-gel combustion method. The phase evolution, morphologies and absorbency of the synthesized powders were characterized by X-ray diffraction (XRD), Field emission scanning electronic microscope (FESEM), Fourier transform infrared spectroscopy (FTIR) and UV-3101PC spectrophotometer (UVPC), respectively. XRD and FESEM results showed that pure SmBO3 phase was obtained at 750 °C, with an average original particle size of about 100 nm. FTIR showed that there were apparently concentrated absorbent peaks between 500 and 1400 cm−1. Moreover, the reflectivity of the powders apparently decreased at the wavelength between 1.05 and 1.15 μm. Therefore, SmBO3 might be a kind of absorbent material for infrared laser.

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.