Morphology and optical properties of Mg and Sr doped CaF2 nanocrystals

Magnesium (Mg) and Strontium (Sr) doped Calcium fluoride nanocrystals were synthesized by co-precipitation method. The cubic structure of the samples was confirmed by Powder X-ray diffraction. The average crystallite size of Mg doped samples was found to be ~ 25 nm whereas in Sr doped one it was ~ 35 nm. The morphological features revealed that the nanocrystals were agglomerated, crispy and porous. The as-prepared samples showed the presence of hydroxyl groups. The optical absorption spectrum of as-prepared Mg doped samples showed a strong absorption band peaked at ~ 233 nm whereas the Sr doped one showed a prominent absorption peak at 248 nm. A strong PL emission was observed at ~ 300 nm in Mg doped samples. However, the Sr doped samples showed two prominent emissions at ~ 345 and 615 nm.     

Anisotropic optical properties of pure and doped polyacetylene

Optical absorption and reflection measurements have been carried out on pure and doped polyacetylene films. The absorption data are consistent with a model of (CH)_X as a direct gap quasi-l d semiconductor; doping with AsF₅ or iodine introduces absorption within the gap, but appears to leave the interband transition intact. The anisotropic reflectance from partially aligned films and the increased optical anisotropy upon doping provide evidence of quasi-l d behavior of the semiconducting pure polymer and the metallic doped polymer.     

Structural and optical properties of cobalt doped ZnO nanocrystals

Zn_1−xCo_xO nanocrystals with nominal Co doping concentrations of x = 0–0.1 were synthesized through a simple solution route followed by a calcining process. The doping effects on the structural, morphological and optical properties were investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman, absorption and luminescence spectroscopy. The results indicated that a small amount of Co ions were incorporated into ZnO lattice structure, whereas the secondary phase of Co₃O₄ was segregated and precipitated at high Co doping concentrations, the solid solubility of Co ions in ZnO nanocrystals could be lower than 0.05. The spectra related to transitions within the tetrahedral Co²⁺ ions in the ZnO host crystal were observed in absorption and luminescence spectra.     

不同价态Mn掺杂InN电子结构、磁学和光学性质的第一性原理研究

采用密度泛函理论体系下的广义梯度近似GGA+U平面波超软赝势方法,在构建了纤锌矿结构的InN超胞及三种不同有序占位Mn~(2+),Mn~(3+)价态分别掺杂InN超胞模型,并进行几何优化的基础上,计算了掺杂前后体系的电子结构、能量以及光学性质.计算结果表明:Mn掺杂后体系总能量和形成能降低,稳定性增加,并在费米能级附近引入自旋极化杂质带,体系具有明显的自旋极化现象.掺杂不同价态的Mn元素对体系电子结构和磁学性质产生了不同的影响.电子结构和磁性分析表明掺杂体系的磁性来源于p-d交换机制和双交换机制的共同作用,Mn~(3+)价态掺杂有利于掺杂体系的居里温度达到室温以上.与未掺杂InN相比,不同价态Mn元素掺杂后体系的静态介电函数显著增大,掺杂体系介电函数虚部和吸收光谱在低能区域出现了较强的新峰,分析认为这些新峰主要来自与费米能级附近自旋极化杂质带相关的跃迁.     

High-pressure and optical properties of lanthanum magnesium hexa-aluminate doped with Mn (LMA:Mn) laser material

The effect of hydrostatic pressure on the emission spectra and fluorescence lifetime (τ) of Mn²⁺ in LaMgAl₁₁O₁₉ (LMA) crystals up to 101 kbar has been studied at room temperature. From the position of the peak (⁴T₁ → ⁶A₁ transition) in the emission spectra, we estimated that the pressure induced red-shift. A variation, slowly decreasing, in the fluorescence lifetime (τ) values for ⁴T₁ → ⁶A₁ transition was observed. The pressure-induced red-shift and lifetime variation could be described by simple models. In the considered pressure range (0-101 kbar), a good agreement between the experimental values and theoretically predicted values was obtained.     

Microstructural and magnetic properties of Ax:Zn1-xO (A=Mn,Gd and Mn/Gd) nanocrystals

We report the microstructural and magnetic properties of transition (3d) and rare earth (4f) metal substituted into the A_x:Zn_1?xO (A=Mn, Gd and Mn/Gd) nanocrystal samples synthesized by solgel method. The structural properties and morphology of all samples have been analysed using X-ray diffraction (XRD) method and scanning electron microscopy. The impurity phase in the XRD patterns for all samples is not seen, except (Mn/Gd):ZnO sample where a very weak secondary phase of Gd₂O₃ is observed. Due to the large mismatch of the ionic radii between Mn²⁺ and Gd³⁺ ions, the strain inside the matrix increases, unlike the crystallite size decreases with the substitution of Mn and Gd into ZnO system. A couple of additional vibration modes due to the dopant have been observed in Raman spectrum. The magnetic properties have been studied by vibrating sample magnetometer. The magnetic hysteresis shows that Mn:ZnO and Gd:ZnO have soft ferromagnetic (FM) behaviour, whereas (Mn/Gd):ZnO has strong FM behaviour at room temperature (RT). The enhancement of ferromagnetism (FM) in (Mn/Gd):ZnO sample might be related to short-range FM coupling between Mn²⁺ and Gd³⁺ ions via defects potential and/or strain-induced FM coupling due to the expansion lattice by doping. The experimental results indicate that RTFM can be achieved by co-substitution of 3d and 4f metals in ZnO which can be used in spintronics applications.     

Synthesis and magnetic properties of Mn doped ZnO nanowires

Mn doped ZnO nanowires have been synthesized using a simple autocombustion method. The as-synthesized Mn doped ZnO nanowires were characterized by X-ray diffraction and transmission electron microscopy. An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Mn concentration. Optical absorption studies show an increment in the band gap with increasing Mn content, and also give evidence for the presence of Mn²⁺ ions in tetrahedral sites. All Zn_1−xMn_xO (0≤x≤0.25) samples are paramagnetic at room temperature. However, a large increase in the magnetization is observed below 50 K. This behavior, along with the negative value of the Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicate ferrimagnetic behavior. The origin of ferrimagnetism is likely to be either the intrinsic characteristics of the Mn doped samples, or due to some spinel-type impurity phases present in the samples that could not be detected.     

Synthesis and magnetic properties of Mn doped CuO nanowires

Study of diluted magnetic semiconductor nanowires is one of the important topics in materials science. By using Mn-Cu alloy as the starting material, Mn doped CuO nanowire arrays have been synthesized in air at the temperature of 550 °C. X-ray diffraction measurements and scanning electron microscopic study shows that the nanowires were grown on Cu₂O substrate. Transmission electron microscopic study shows the single crystal property of the nanowires. Magnetic measurements show ferromagnetic property in the Mn doped CuO nanowires with the critical temperature higher than 80 K.     

Structural,optical, and multiferroic properties of single phased BiFeO3

A soft chemical coprecipitation method has been proposed for synthesis of nano-sized multiferroic BiFeO₃ (BFO) powders. The X-ray diffraction pattern confirms the perovskite structure of BFO and Rietveld refinement reveals the existence of rhombohedral R3c symmetry. Crystallite size and strain value are studied from Williamson–Hall (W–H) analysis. The transmission electron microscope (TEM) image shows that the particle size of BFO powders lies between 50–100 nm. 4A₁ and 7E Raman modes have been observed in the range 100–650 cm^?1 and a prominent band centered around 1150–1450 cm^?1 have also been observed corresponding to the two-phonon scattering. Differential Thermal Analysis (DTA) shows the existence of two prominent peaks at 330 ^°C and 837 ^°C corresponding to the magnetic and ferroelectric ordering, respectively. From the temperature dependent dielectric studies, an anomaly in the dielectric constant is observed at the vicinity of Neel temperature (T _N ) indicating a magnetic ordering. Also, BFO shows antiferromagnetic behavior measured from the magnetic studies.     

过渡金属TM(V,Cr,Mn)掺杂ZnS的电子结构和磁性

采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法,对过渡金属V、Cr、Mn掺杂ZnS的超晶胞体系进行了几何结构优化,计算了晶格常数、电子结构与磁学性质.研究结果表明:掺入V,Cr后,ZnS表现出明显的半金属性,而掺入Mn后,半金属性不明显;掺入过渡金属TM(V,Cr,Mn)后系统产生的磁矩主要有杂质的3d态电子贡献,且磁矩的大小与过渡金属的电子排布有关.     

Structural and magnetic properties of Cr and Mn doped InN

We present a detailed magnetic characterization of Cr and Mn doped InN films be means of superconducting quantum interference device magnetometry and X-ray magnetic circular dichroism. The InN:Cr films exhibit ferromagnetic behavior up to 300 K in a doping region from 2% to 8% without detectable phase segregation. The easy axis of magnetization is found to be in the film plane. On the contrary, Mn-doped films show signatures of phase segregation and paramagnetic behavior.     

Mn掺杂ZnO薄膜的结构及光学性能研究

通过脉冲激光沉积(PLD)法在SiO₂基片上制备了不同含量的Mn掺杂ZnO薄膜.X射线衍射、X射线能谱、原子力显微镜与紫外-可见分光光度计测试结果表明：少量的Mn离子的掺杂并没有改变薄膜的结构，薄膜具有(103)面的择优取向；PLD法制备的ZnO薄膜的成分与靶材基本一致，实现了薄膜的同组分沉积；薄膜表面比较平坦，起伏度小于80nm，颗粒尺寸主要集中在25nm附近；但是Mn离子的掺杂改变了ZnO薄膜的禁带宽度，随Mn掺杂含量的增加，ZnO薄膜的禁带宽度增加；当薄膜中Mn含量从6%增加到 关键词： PLD ZnO薄膜 Mn掺杂 吸收谱     

Structural and optical properties of Mn doped ZnS semiconductor nanostructures

Manganese doped zinc sulphide nanoparticles were fabricated by adopting an inexpensive solution growth route. Different samples were fabricated by varying Mn concentrations. UV-VIS study reveals blue-shift on the onset of absorption and hence enhancement in the optical band gap upto 0.75 eV, indicating strong quantum confinement. Photoluminescene study for all the samples display characteristic band edge peak at ∼410 nm. The broad peak ∼560–580 nm is ascribed to Mn incorporation. Further, structural investigations were carried out by using X-Ray diffraction and transmission electron microscopy (TEM).     

Mechanoluminescence and thermoluminescence of Mn doped ZnS nanocrystals

This paper reports the synthesis of ZnS:Mn nanocrystals by the chemical route in which mercaptoethanol was used as the capping agent. The particle size of such nanocrystals was measured using XRD and TEM patterns and was found to be in between 3and 5 nm. It was found that the peak position of TL glow curve and the TL intensity of ZnS:Mn nanoparticles increases as the particle size is decreased. The isothermal decay technique is used to determine the trap-depth. The stability of the charge carriers in the traps increase with the decrease in size of the nanoparticles. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap-depth with decreasing particle size. When a ZnS:Mn nanocrystal is deformed the peak intensity I_m increases linearly with the increasing height of the load. After I_m, initially the ML intensity decreases at a fast rate, and later on it decreases at a slow rate. The ML in ZnS:Mn nanocrystals can be understood on the basis of the piezoelectrically induced electron detrapping model.     

Mn掺杂ZnO纳米棒阵列的制备及其磁学性质研究

在95 ℃条件下通过水热方法制备出垂直于ITO基底高密度均匀生长的Mn掺杂ZnO（ZnO：Mn）纳米棒阵列. 纳米棒的直径约为100纳米,长约1微米,且沿［001］方向生长. XRD和XPS结果证实了Mn以替位方式掺杂到纳米棒中,并且掺杂浓度与反应物中的Mn离子浓度似呈正比关系. 所制备的ZnO：Mn纳米棒在室温均有铁磁性,其饱和磁化强度随反应物中Mn离子浓度的提高,饱和磁化强度呈现出先增大,5at.%时达到最大值,0.11 emu/g,然后减小. 铁磁性来源于取代Zn离子的Mn离子之间的铁磁交换相互作用.     

Thermoluminescence mechanism of Mn, Mg and Sr doped calcite

In this work, the thermoluminescence properties of synthetic crystals of doped calcite were studied. Samples were doped with Mn²⁺, Mg²⁺ or Sr²⁺, either individually or simultaneously with more than one of these impurities. TL glow curves, partial heating measurements, isometric curves, emission spectra and thermal treatment were performed, in order to investigate the role played by the impurities in the TL glow peaks of calcite. We conclude that the crystals doped with Mn²⁺ show five TL peaks with emission spectra due only to the Mn²⁺. The relative intensity of these peaks is closely related to the other divalent dopant added in the solution (Sr²⁺ or Mg²⁺). These results suggest that although Sr²⁺ and Mg²⁺ act as TL activators stabilising slightly different electron traps, they are not directly connected to the Mn²⁺ luminescence centre.     

Magnetic, electronic, dielectric and optical properties of Pr(Ca:Sr)MnO 3

The charge-ordered perovskite Pr_0.65Ca_0.28Sr_0.07MnO₃ was investigated by means of magnetic susceptibility, specific heat, dielectric and optical spectroscopy and electron-spin resonance techniques. Under moderate magnetic fields, the charge order melts yielding colossal magnetoresistance effects with changes of the resistivity over eleven orders of magnitude. The optical conductivity is studied from audio frequencies far into the visible spectral regime. Below the phonon modes hopping conductivity is detected. Beyond the phonon modes the optical conductivity is explained by polaronic excitations out of a bound state. ESR techniques yield detailed informations on the (H,T ) phase diagram and reveal a broadening of the linewidth which can be modeled in terms of activated polaron hopping. Received 9 August 2000