Rui Xia Zhong

The Influence of B2O3 on the Luminescence Behavior of ZnGa2O4 Phosphor at Different Sinter Temperatures

ZnGa2O4 phosphors have been synthesized by solid state reaction at different temperatures with different B2O3 concentration incorporated in the experiments. All samples present green (509 nm) and red (696 nm) emission bands under ultraviolet excitation (250 nm), whose intensity changes because of the increasing B2O3 contents. The green and the red long afterglow have been observed after removing the ultraviolet light and the performance largely improves with the introduction of B2O3. The effects of the doping contents of B2O3 as well as the sintering temperatures on the luminescent properties of the obtained products have been investigated. The introduction of B2O3 changes the ratio of the two emitting centers and increases the depth of the trap centers in the samples.

Preparation and Characterization of LaAlO3 via Sol-Gel Process

Lanthanum aluminate powders were synthesized by sol-gel process with metal nitrates as raw materials, 2-methoxyethanol/water as solvent and citric acid as chelating agent. The influence of this techniques (the amount of citric acid, pH value, calcination temperature and the ratio of 2-methoxyethanol/water) on the lanthanum aluminate powders were studied. The XRD shows pure LaAlO3 powders could be obtained after calcining at 600-900 °C. The SEM analysis indicates that the LaAlO3 particles are uniform and nanosized with a range of about 40-70 nm, which is slightly larger than the estimated particle size using Scherrer formula.

Comparative Studies of Multiferroic BiFeO3 Powders Prepared by Hydrothermal Method versus Sol-Gel Process

Multiferroic BiFeO3 powders were synthesized by two methods: sol-gel process and hydrothermal method. The synthesized powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and particle size distribution analysis. The results obtained by XRD, which is consistent with 86-1518 JCPDS card, show that powders prepared by hydrothermal method are composed of the single phase with the trigonal structure (perovskite-type). It can be found by particle size distribution analysis that the particle size of the samples prepared by sol-gel process is finer and more uniform than that of the samples synthesized by the hydrothermal method. The SEM images of samples depicts that the synthesized BiFeO3 powders are united and the average grain size of hydrothermal processed samples is significantly large as compared to the sol-gel derived sample.

Influence on Red Long-Lasting Phosphorescence due to Different Doping Concentrations of ZnGa2O4:Cr3+

High temperature solid state reaction has been used to prepare the new red long-lasting phosphorescence (LLP) material ZnGa2O4:Cr3+ with different doping concentration. The afterglow properties of the samples have been investigated. Our study has shown that ZnGa2O4 samples without Cr3+ doping have blue-green afterglow. While the blue-green afterglow has disappeared and the red long-lasting phosphorescence according to the Cr3+ luminescence center covering 650 nm-750 nm has been observed when Cr3+ has been doped. In terms of brightness and decay time of the afterglow, the red afterglow and the blue-green afterglow have been entirely different. In this article the influence on LLP due to different doping concentrations of ZnGa2O4:Cr3+ has been discussed and the possible LLP mechanism has been proposed.

Influence on Afterglow Spectra due to Different Phases of Zn3(PO4)2: Mn2+

High temperature solid state reaction has been used to prepare Zn3(PO4)2: Mn2+. XRD analysis shows that different phases have been generated with different Mn2+ doping concentration at the same sintering temperature. Low Mn2+ doping concentration is conducive to form α phase, while γ is in favor of high Mn2+ doping concentration. In α phase, the emission spectrum of Mn2+ is a wide emission band peaking at 542 nm, green fluorescence. In γ phase, the emission spectrum of Mn2+ is a wide emission band peaking at 608 nm, red fluorescence. In the both phases, green and red afterglows have been observed. The red afterglow in γ phase has stronger initial brightness and longer afterglow decay time than the green afterglow in α phase, the reason of which lies in the larger trap concentration in γ phase.

Preparation and Dielectric Properties of La Doped Bi2Al4O9

A series of (Bi1-xLax)2Al4O9 (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.40) ceramics were prepared by sol-gel method with sintering process. Doping dependent investigations were carried out to show the influence of La atom on the structural stability. The products were characterized using X-ray diffraction, scanning electron microscopy. This showed that the second phase is increased gradually by La doping. When the value of La is 0.4, the main phase tends to become LaAlO3. Details on dielectric properties are reported. The permittivity of as-prepared doped samples increases slightly compared to pure Bi2Al4O9 and excellent frequency stability is exhibited.

Synthesis and Characterization of Bi2Al4O9 Powders

Bi2Al4O9 powders were prepared by sol-gel process. The precursors were heated at 500-800°C for 2h to obtain Bi2Al4O9 powder and X-ray diffraction (XRD), Differential thermal analysis (DTA), thermogravimetric analysis (TG), field emission scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize precursor and derived oxide powders. XRD analysis show that the powder is still amorphous after calcined at 500°C. The peaks of Bi2Al4O9 become sharp after calcined at 575°C though still existing some amorphous phase. After calcining at 675-800°C, the powder has fully turned into pure Bi2Al4O9 phase. The crystallization process can also be confirmed by DTA-TG and IR. Calcining the precursor at 575°C, the absorption bands at 527 cm-1, 738 cm-1, 777 cm-1, and 919 cm-1are observed, which are assigned to Bi2Al4O9 and becoming stronger and sharper with the increase of temperature.

Effect of Sc Doping on Ferroelectric and Dielectric Properties of Bi0.9La0.1FeO3 Thin Film by Sol-Gel Process

Pure Bi0.9La0.1Fe1-xScxO3 (x = 0, 0.05, 0.10, 0.15, 0.20) (BLFSO) thin films were deposited on conductive indium tin oxide (ITO)/glass substrates through a simple sol-gel process. The effect of Sc doping on the XRD, microstructure, dielectric and ferroelectric properties of BLFO films was studied. Compared to counterparts of Bi0.9La0.1FeO3 (BLFO) film, the grain refinement of all films is obvious. When the value of Sc is 0.15, the double remanent polarization 2Pr is effectively enhanced with the extreme value of 17.7µC/cm2. The dielectric constant exhibits a trends of increase firstly and then decrease with the increase amount of scandium level.

Energy Transfer and Green/Red Phosphorescence in γ-Zn3(PO4)2:Mn2+, Ga3+

In this letter, γ-Zn3(PO4)2: Mn2+ phosphors have only one emission band centered at 620 nm while two emission bands are observed in γ-Zn3(PO4)2: Mn2+, Ga3+, which are respectively centered at 507 nm and 620 nm. The spectral overlap between the green emission band and the excitation band monitored at 620 nm, which supports the occurrence of the energy transfer from Mn2+ (CN=4) to Mn2+ (CN=6), has been studied. The influence of Ga3+ ions on luminescence and long lasting phosphorescence properties of Mn2+ in phosphor γ-Zn3(PO4)2: Mn2+, Ga3+ are also investigated. It is found that the green/red phosphorescence performance of Mn2+ ion such as brightness and duration is largely improved when Ga3+ ion is co-doped into the matrix in which Mn2+ ion acts as luminescent center and Ga3+ ion plays an important role of electron trap.