Luminescence Characterization of Mg Doped Y_2O_2S:Ti Long Afterglow Phosphor

Y1.94-xMgxO2S:0.06Ti (0≤x≤0.10) phosphors with long afterglow were synthesized by solid state reaction route. The photoluminescence spectra, decay curves, thermoluminescent spectra and chromaticity coordinate curves were investigated. The results show that the luminescence intensity of Y1.94-xMgxO2S:0.06Ti (0≤x≤0.10) phosphors decrease gradually with increasing Mg2+ ion content, and the shape of luminescence spectra and chromaticity coordinate change as well. Furthermore, two thermoluminescent peaks in single Ti-doped Y2O2S sample are found at 91.8 and 221.5 ℃, respectively. Nevertheless, significant different spectra were found for the Mg, Ti co-doped Y2O2S samples that three thermoluminescence peaks appear at 52.3, 141.7 and 226.8 ℃, respectively. These results indicate that the co-doped Mg ion changes the inherent trap depth of single Ti-doped Y2O2S:Ti phosphor, and induces simultaneously a new trap level in the Y1.94-xMgxO2S:0.06Ti phosphor. Based on the analysis of thermoluminescent spectra, photoluminescent spectra, decay curve and crystal structure defect, it was proposed that the varied structure defect and introduced new trap level by the doped Mg2+ ions should be responsible for reducing luminescence intensity and varying color in the Y1.94-xMgxO2S:0.06Ti phosphor.

Preparation and Luminescence Properties of Y_2O_3:Eu^(3+) Nanorods via Post Annealing Process

Yttrium oxide doped with europium has a great prospective for FED and PDP phosphor application. In present study, the precursor of yttrium oxide hydroxide nitrate nanorod, which was prepared via hydrothermal reaction route using PEG-6000 as template from the starting Y(NO3)3 and KOH reactant system, was used to prepare Y2O3:Eu3+ nanorod via a post annealing process during which the precursor with adjustable shape and size was transformed to final Y2O3:Eu3+ product. XRD, field emission scanning electron microscopy (FE-SEM) and photoluminescence spectra (PL) were used to characterize the crystalline, morphology and luminescence properties of as-formed Y2O3:Eu3+ products synthesized at different post annealing temperatures, respectively. The results indicate that grain morphology of obtained Y2O3:Eu3+ product was nanorod with a mean diameter of about 40～60 nm and length of about 500～700 nm, the nanorod structure and morphology of obtained Y2O3:Eu3+ product maintained during post annealing process and the size varied slightly with different annealing temperatures. Pure cubic Y2O3:Eu3+ phase was formed and the size was the smallest at annealing treatment of 500 ℃. Under the annealing temperature below 500 ℃ its diameter increased with increasing annealing temperature, and remained in a stable size when the annealing temperature was above 500 ℃. The PL spectra of excitation spectra of Y2O3:Eu3+ product show that it exhibits excitation band located at about 395 and 468 nm, respectively. Above two excitation bands could be ascribed to the transition 4f-4f of Eu3+ ions in the Y2O3 host. On the other hand, the main emission peaks of the as-prepared products could be ascribed to the Eu3+ ions transition from 5D0 to 7F2. Furthermore, the luminescent intensity was improved about three times when the annealing temperature increased from 500 to 1000 ℃.

Effect of niobium addition on magnetization reversal behavior for SmCo-based magnets with TbCu7-type structure

The effect of Nb addition on the microstructure and magnetic properties of nanocrystaUine Sm（CobaiNbxZr0.02）7 permanent magnet were investigated, The magnetization reversal behavior for ball milled Sm（CobaiNbxZr0.02）7 samples with high coercivity was investigated by analyzing hysteresis curves and recoil loops of demagnetization curves. Nb addition proved to result in relevant improvement in the magnetic properties, especially in the coercivity He. It was shown that the magnetic properties of Sm（CobalNbx- Zr0.02）7 nanocrystalline magnets were improved by an additional 0.06 at.% Nb. In particular, Hc was improved from 602 to 786 kA/m at room temperature. The maximum value of the integrated recoil loops area for 0.06 at.% Nb-doped samples of 1.81 kJ/m3 was much lower than that of the Nb-free sample, which could be explained by a smaller recoverable portion of the magnetization remaining in the Nb-doped sample when the applied field was below the coercivity Hc. The nucleation field Hn for irreversible magnetization reversal of the magnetically hard phase were calculated by analyzed in terms of the△Mirrev-H curve and the Kondorsky model.

Magnetic properties and magnetization behavior of SmCo-based magnets with TbCu_7-type structure

The nanocrystalline magnets with nominal compositions of Sml_xLuxCo6.8Zr0.2 （x-=0, 0.2, 0.4, 0.6） were prepared directly by the intensive milling. The effects of Lu content on the phase structure, the magnetic properties, and magnetization behaviors were also investigated. The XRD patterns of the as-milled samples showed a single SmCo7 phase with TbCu7 structure. Lu addition was proved to result in relevant improvements in the microstructure and magnetic properties, especially in the maximum energy product （BH）max. It was shown that a higher maximum energy product and coercivity of about 17.47 kJ/m3 and 473.45 kA/m were obtained in the sample with x=0.2. From the analysis of the magnetization reversal behavior, it was found that a stronger intergrain exchange coupling interaction was observed in the samples with Lu-doping. From the studies of the coercivity mechanism, it was shown that nucleation model was the dominant magnetization reversal process at the elevated temperature.

Crystallization kinetics and magnetization behavior of RE_(3.5)Fe_(66.5)Co_(10)B_(20)(RE=Pr, Nd) nanocomposite ribbons

The influence of hard magnetic phase on the crystallization kinetics and magnetization behavior in nanocomposite RE3.5Fe66.5Co10B20（RE = Pr, Nd） ribbons prepared by melt-spinning was studied. Differential scanning calorimeter（DSC） measurement of the as-cast meltspun amorphous ribbons during the crystallization process shows that precipitation energy of Pr2Fe14 B phase is higher than that for Nd2Fe14 B phase, confirmed by X-ray diffraction（XRD） patterns. It can be explained by the different radii of Pr and Nd atoms. Scanning electron microscopy（SEM）images indicate that the average grain size in Pr3.5Fe66.5Co10B20 ribbon is smaller than that in Nd3.5Fe66.5Co10B20,resulting in an enhancement of exchange coupling between hard and soft phases. It is responsible for the better hard magnetic properties in Pr3.5Fe66.5Co10B20. In addition, the process of magnetization reversal of nanocomposite RE3.5Fe66.5Co10B20（RE = Pr, Nd） ribbons was discussed in detail by the recoil loops.

Microstructure,magnetic properties of hexagonal barium ferrite powder based on calcination temperature and holding time

In this paper,single-phase and fine-grain hexagonal barium ferrite powder was prepared based on the optimal calcination condition.The influence of calcination conditions including temperature and holding time on microstructure and magnetic properties of powder were studied in detail.Firstly,θ-2θ scan X-ray diffraction(XRD) results reveal that it is hard to obtain single phase of powder when the calcination temperature is lower than 850℃.In addition,the calcination time for single phase of barium ferrite powder was reduced with the increase in calcination temperature.Scanning electron microscopy(SEM) images and magnetic hysteresis loops show that the condition of low temperature and long holding time is beneficial for obtaining homogeneous size of grain and excellent magnetic properties.Consequently,hexagonal barium ferrite powder with uniform grain size of~180 nm,high purity and excellent magnetic properties is obtained at optimal calcination condition of 850℃-10.0 h.

Crystallographic alignment and magnetic anisotropy in melt-spun Nd-Fe-B/α-Fe composite ribbons with different neodymium contents

Crystallographic alignment and magnetic anisotropy were studied for NdxFe94–xB6 （x=8,9,10,11） ribbons prepared via melt-spinning. Effect of Nd content and wheel speed on the crystal structure and magnetic properties of the ribbons was investigated. Both the free and wheel side of the ribbons could obtain strong c-axis crystal texture of Nd2Fe14B phase perpendicular to the ribbons surface at low wheel speed,but the texture weakened gradually with the increase of the wheel speed. Increase of Nd content led to better formation of crystal texture in the ribbons,indicating that the α-Fe phase might undermine the formation of crystal texture. Magnetic measurement results showed that the magnetic anisotropy of the ribbons exhibited corresponding behavior with the invariance of the c-axis crystal texture of Nd2Fe14B phase in the ribbons,and the coercivity of the ribbons rose with the increase of both Nd content and wheel speed during melt-spun process.

Magnetization reversal behavior and first-order reversal curve diagrams in high-coercivity Zr-doped α-Fe/Nd_(2)Fe_(14)B nanocomposite alloys

In the present work,the magnetization reversal behavior for the melt spinning(Nd_(0.8)Ce_(0.2))_(2)Fe_(12)Co_(2-x)Zr_(x)B(x=0,0.5)permanent alloys with high coercivity was investigated by analyzing the hysteresis curves and the recoil loops.Compared to the Zr-free alloy,the Zr-doped sample obtains higher magnetic properties:coercivity of H_(cj)=650.5 kA·m^(-1),squareness of H_(k)/H_(cj)=0.76 and maximum energy product of(BH)_(max)=131.0 kJ·m^(-3).The first-order reversal curves(FORCs)analysis was taken to identify optimal conditions of exchange coupling for the Zr-free and Zr-doped alloys.The coercivity mechanism of theα-Fe/Nd_(2)Fe_(14)B nanocomposite alloys was analyzed by the angular dependence of the coercive field as measured for the Zr-doped sample.The results show that the magnetic reverse process of the Zr-doped sample can be explained by the pinning model.