M. Z. Su

Synthesis of Y3Al5O12:Eu3+ phosphor by sol-gel method and its luminescence behavior

Abstract The Eu 3+ -doped Y 3 Al 5 O 12 phosphor ultrafine powders were synthesized by the sol–gel method using metal alkoxide at the lower temperature of 1000°C. The formation process and structure of the phosphor powders were investigated by means of TG-DTA, XRD and SEM. It has been found that the phosphor powders were amorphous up to 700°C and changed into the single phase YAG at about 1000°C, that is, 600°C lower than that required for the constituent oxide mixtures. The resulting ultrafine, phase-pure, cubic yttrium aluminum garnet (YAG) phosphor powders were obtained. In the course of the phosphor transformation from non-crystalline state to crystalline state, both the emission intensity and the site symmetry of Eu 3+ in the phosphors varied noticeably. The Eu 3+ emission intensity of 5 D 0 → 7 F 1 and 5 D 0 → 7 F 2 versus Eu 3+ concentration and sintering temperature was studied.

Preparation of Nd-Fe-B based magnetic materials by soft chemistry and reduction-diffusion process

Abstract Starting from superfine precursors, Nd-Fe-B based magnetic materials, Nd2Fe14B and Nd2Fe12Co2B, have been prepared by reduction-diffusion reaction at relative low temperature. The boride precursors used in the reactions, ie., Co2.0B1.2 and Fe1.0B0.25, were obtained from the reduction of CoCl2 and FeSO4 with NaBH4 in aqueous solution at room temperature. The other precursors, Nd2O3 and Fe2O3 were obtained by a polymer network gel process. The obtained Nd2Fe14B and Nd2Fe12Co2B materials are fine crystalline powders which show quite strong magnetic anisotropy. The particle sizes of these materials can be controlled to about a few microns without using mechanical milling processes.

Does Ce4+ play a role in the luminescence of LaPO4:Ce?

The influence of lithium on the structure and the luminescence properties of LaPO4:Ce have been studied. Energy transfer between Ce3+ and Ce4+ was proved to play an important role in the luminescence of this material. This energy transfer depends not only on the concentration of the Ce4+, but also on the distribution of the Ce3+ and Ce4+, owing to its inter-valence charge nature. Introducing lithium may affect the spatial and valence distribution of the cerium in this material, and subsequently influence the luminescence of Ce3+.

Synthesis of Nd2Fe17 by reduction-diffusion process

Abstract Nano-scale rare earth and transition metal oxides, obtained via a sol-gel process, were used as precursors to synthesize the intermetallic compound Nd2Fe17 with the reduction-diffusion method. The product obtained is a single Nd2Fe17 phase. The particles of the produced alloy, which can be controlled by the particle size of the precursors, are narrowly distributed with a typical size of a few micrometers.

X-ray storage phosphors, their properties and mechanism

Abstract X-ray storage phosphors doped with rare earth ions were synthesized and their properties with respect to applications were characterized. A simplified band model for the photostimulated luminescence (PSL) processes of Ce, Tb, Sm and Sm doped BaFX phosphors is proposed. For the PSL mechanism of divalent europium doped BaFX (XCl or Br) we found some special characteristics. On the basis of many experimental results we think that during photostimulation electrons are excited from F(X − ) centers to a higher energy level and prefer transfer through tunneling rather than via the conduction band to recombine with the trapped holes, thus giving rise to the characteristic luminescence of the doped divalent europium ions.

Reaction mechanism for the solid state synthesis of LaPO4:Ce,Tb phosphor

Abstract LaPO 4 :Ce,Tb is an efficient green component of trichromatic lamp phosphors. It is usually prepared by solid state reaction of a blend of (NH 4 ) 2 HPO 4 , Tb 4 O 7 and CeO 2 with or without Li 2 CO 3 flux. This reaction mechanism has been investigated by differential thermal analysis, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy. Experimental results show that at ∼ 200 °C (NH 4 ),HPO 4 decomposes to form syrupy P 2 O 5 ·χH 2 O. As the firing temperature is increased to 600 °C (in the presence of Li 2 CO 3 ) and 800°C (in the absence of Li 2 CO 3 ) syrupy P 2 O, begins to react with rare earth oxides to form mixed rare earth orthophosphates. Up to 1000 °C and 1400 °C, respectively, these two reactions go to completion. Their reaction rates change linearly as the reciprocal temperature and with different slopes, from which activation energies are estimated to be 22 and 35 kcal mol −1 , respectively. Reactions appear to be diffusion-limited. Thermal quenching of luminescence of LaPO 4 :Ce,Tb can be minimized by the addition of Li 2 CO 3 in the reaction mixture.

An alternative approach to the finely crystalline powder of rare earth-transition metal alloys

Abstract Small particulate alloys, Sm 2 Fe 7 , Nd 2 Fe 7 , NdFe 10 Mo 2 and NbFe 11 Ti, have been obtained by reduction-diffusion reactions from nanoscale precursors. The nanoscale oxide precursors, such as rare earth and transition metal oxides, were produced by sol-gel methods. After a preliminary H 2 reduction treatment, the precursors were reduced by CaH 2 under mild conditions. The obtained alloys are crystalline powders with small particle sizes and uniform size distributions.

On structural and magnetic properties of ErFe11WZx (Z = H, N)

Abstract Intermetallic compound ErFe11W has been synthesized by a reduction-diffusion process with superfine iron powder as a starting material. The compound and the interstitial derivatives ErFe11WZx (Z = N, H) crystallize in the tetragonal ThMn12 structure and the tungsten atoms occupy the 8i site. The introduction of nitrogen atoms into the ErFe11W compound easily changes the magnetization direction from the c-axial to the basal plane and the Curie temperature and saturation magnetization increase simultaneously.

On Synthesis and Magnetic Properties of Nd(Fe, Mo, Ti)12Zx (Z=N, H)

NdFe10+xMo2−2xTix compounds with 0≤x≤1.0 have been prepared by using the reduction–diffusion process with superfine precursors as starting materials. With increasing Ti-content, the intrinsic magnetic properties, such as the Curie temperature, saturation magnetization and magnetocrystalline field, are improved. The interstitial compounds NdFe10+xMo2−2xTixZy (Z=N, H) were obtained and exhibit significant enhancement of the intrinsic magnetic properties upon nitrogenation.

On the synthesis and magnetic properties of LnFe10Si2Zx (Z=N,H and Ln=Tb, Er)

Abstract Single-phase products of LnFe 10 Si 2 (Ln=Tb, Er) have been synthesised by a reduction–diffusion process with superfine iron metal as the starting material. The nitrogen interstitial compounds were obtained by direct reaction with nitrogen at high pressure. The introduction of nitrogen changes the easy magnetization direction from basal plane to the c -axis for TbFe 10 Si 2 and from the c -axis to basal plan for ErFe 10 Si 2 .