Structural, spectroscopic and crystal field analyses of Ni2+ and?Co2+ doped Zn2SiO4 powders

In this paper we presented structural and spectroscopic study of zinc silicate powder samples doped with divalent nickel and cobalt ions. Results of the Rietveld structural refinement, combined with optical spectroscopic study and theoretical crystal field calculations, are presented and discussed. X-ray diffraction studies were performed to establish reliable structure of the doped samples; in this way the interionic distances and chemical bond angles in Zn₂SiO₄:Co²⁺ and Zn₂SiO₄:Ni²⁺ were calculated and are reported for the first time. The room temperature reflection spectra of the prepared samples were measured in a spectral region from 4000 to 50000 cm^?1. The exchange charge model of crystal field has been applied to analyze the experimental spectra and assign all observed details in the spectra to the corresponding electronic transitions between the Co²⁺ and Ni²⁺ crystal field energy levels. The only input information for the model calculation was the experimentally obtained structural data, which were used for the calculations of the crystal field parameters with subsequent diagonalization of the crystal field Hamiltonian for both ions. Agreement between the calculated and experimentally detected energy levels of impurity ions was good. On the basis of the crystallographic and crystal field studies it was established that there exists a systematic trend of preferential occupation of one out of two possible crystallographic sites (namely, Zn2) for both impurity ions.     

Luminescence properties of green emission of SiO2/Zn2SiO4:Mn nanocomposite prepared by sol–gel method

Green light emitting Mn²⁺ doped Zn₂SiO₄ particles embedded in SiO₂ host matrix were synthesized by a sol–gel method. After the incorporation of ZnO:Mn nanoparticles in a silica monolith using sol–gel method with supercritical drying of ethyl alcohol in two steps, it was heat treated in air at 1200 °C for 2 h in order to obtain the SiO₂/α-Zn₂SiO₄:Mn nanocomposites. The microstructure of phosphor crystals was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). XRD results indicate that the pure phase α-Zn₂SiO₄ with rhombohedral structure was obtained after thermal treatment at 1200 °C. The SiO₂/α-Zn₂SiO₄:Mn nanocomposites with a Mn doping concentration of 1.5 at% exhibit two broadband emissions in the visible range: a strong green emission at around 525 nm and a second one in the range between 560 and 608 nm. This nanocomposite with a Mn doping concentration of 0.05 shows the highest relative emission intensity. Upon 255 nm excitation, the luminescence decay time of the green emission of Zn₂SiO₄:Mn around 525 nm is 11 ms. The luminescence spectra at 525 nm (⁴T₁–⁶A₁) and lifetime of the excited state of Mn²⁺ ions-doped Zn₂SiO₄ nanocrystals are investigated.     

Correlation between Light Emissions from Amorphous-Si：H/SiO2 and nc-Si/SiO2 Multilayers

We investigate the properties of light emission from amorphous-Si：H/SiO2 and nc-Si/SiO2 multilayers （MLs）. The size dependence of light emission is well exhibited when the a-Si：H sublayer thickness is thinner than 4 nm and the interface states are well passlvated by hydrogen. For the nc-Si/Si02 MLs, the oxygen modified interface states and nanocrystalline silicon play a predominant role in the properties of light emission. It is found that the light emission from nc-Si/SiO2 is in agreement with the model of interface state combining with quantum confinement when the size of nc-Si is smaller than 4 nm. The role of hydrogen and oxygen is discussed in detail.     

Zn2SiO4∶Mn的VUV和UV光谱特性

采用高温固相反应法以硅酸为原料合成了等离子显示用荧光体Zn2 SiO4 ∶Mn ,研究了Zn2 SiO4 ∶Mn的VUV和UV光谱特性 ,表明波长小于 2 0 0nm的部分的基质吸收带主要是氧的 2 p轨道到锌的 3d轨道跃迁产生的 ,波长大于 2 0 0nm的部分的基质吸收带是氧的 2 p轨道到硅的 3p轨道跃迁吸收。在VUV和UV激发下 ,Mn2 +的浓度与发射强度的相关性研究表明 ,在不同区域激发时荧光体的发射强度随着Mn2 +的浓度的变化存在明显不同     

Zn2SiO4：Mn的VUV和UV光谱特性

采用高温固相反应法以硅酸为原料合成了等离子显示用荧光体Zn2SiO4：Mn，研究了Zn2SiO4：Mn的VUV和UV光谱特性，表明波长小于200nm的部分的基质吸收带主要是氧的2p轨道到锌的3d轨道跃迁产生的，波长大于200nm的部分的基质吸收带是氧的2p轨道到硅的3p轨道跃迁吸收。在VUV和UV激发下，Mn^2 的浓度与发射强度的相关性研究表明，在不同区域激发时荧光体的发射强度随着Mn^2 的浓度的变化存在明显不同。     

Zn2 SiO4:Mn,Cd磷光体的长余辉特性

高温固相法合成Zn2SiO4：1．2％Mn,5％Cd长余辉磷光体,对样品进行了X射线衍射分析、光谱分析以及余辉衰减特性测量。分析结果表明,在1050℃下烧结3h的硅酸锌产物为单相。Zn2SiO4：1．2％Mn,5％CdK余辉磷光体在243nm或260nm激发下,发射光谱最大峰值位于521nm处,其色坐标x=0．2301,Y=0．69150在254nm紫外光激发5min后样品的余辉发光在暗室里可持续观察的时间约为1h,与Zn2SiO4：1．2％Mn磷光体比较,显示了更好的余辉特性。     

SiO2/Ge:SiO2/SiO2夹层结构红外光发射的起源

我们借助傅立叶变换红外光谱（FT－IR）以及光致激发谱（PLE）,研究SiO2/Ge:SiO2/SiO2夹层结构红外光发射的起源。谱分析表明,该红外光发射并非起源于纳米锗、硅的量子限制效应以及锗、硅的中性氧空位,而与锗的氧化物紧密相关。PLE的结果证实它们来源于GeO色心TⅡ‘→S0的光学跃迁,给出的GeO电子态模型描述了载流子激发和复合的过程。     

Zn2SiO4∶Mn2+发光材料的低温合成及其发光性能

采用水热合成工艺低温制备了Mn2+掺杂的Zn2SiO4发光材料,采用X射线衍射(X-ray diffraetion,XRD)、扫描电子显微镜(Scanning electron microscope,SEM)对样品的结构和形貌进行观察,并以此分析了水热过程中Zn2SiO4的形成机制.采用吸收光谱、荧光光谱对其光吸收及光...     

Zn2SiO4:Mn2+荧光粉的燃烧法合成及其发光特性

用燃烧法成功合成了Zn2-xsiO4:xMn(0≤x≤0.10)粉末样品并表征了其发光特性.XRD测量结果表明,在600℃下燃烧数分钟、900℃以上进行热处理4 h后,所得样品为单相Zn2-xSiO4:xMn(0≤χ≤0.10,Willemite).监控525 nm发射,测得Zn2-xSiO4:xMn(0＜χ≤0.10)的最强激发峰为Mn2+的6A1→4T1跃迁(约254 nm).254 nm激发下,Zn2-xSiO4:xMn(0＜χ≤0.10)的最强发射峰为Mn2+的3d电子组态内自旋禁戒的4Ti→6AJ跃迁(约525 nm).结果表明,发光强度、最强峰位、最佳激活剂浓度等与初始原料、燃烧温度、燃烧剂的用量、粉末粒度等有关.     

不同制备条件对Zn2SiO4∶Mn2+粉末发光性能的影响

利用溶胶-凝胶法制备了Zn2SiO4∶Mn2 粉末,探讨了体系pH值、热处理温度、煅烧气氛对材料结构和发光性能的影响。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、光致发光(PL)谱等分析手段对Zn2SiO4∶Mn2 粉末的结构、颗粒大小、形貌、发光性能进行了表征。结果表明:溶胶的pH值影响制备的粉体的结晶性和颗粒大小,当溶胶pH值为4.34时,体系水解缩聚反应充分,所得荧光粉的光致发光强度最强;煅烧气氛显著影响荧光粉的发光强度,前驱体在N2(90%) H2(10%)的还原气氛下煅烧得到的发光粉发光强度最强;最佳热处理温度为900℃。     

不同制备条件对Zn2SiO4：Mn^2＋粉末发光性能的影响

利用溶胶-凝胶法制备了Zn2SiO4：Mn^2＋粉末,探讨了体系pH值、热处理温度、煅烧气氛对材料结构和发光性能的影响。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、光致发光（PL）谱等分析手段对Zn2SiO4：Mn2＋粉末的结构、颗粒大小、形貌、发光性能进行了表征。结果表明：溶胶的pH值影响制备的粉体的结晶性和颗粒大小,当溶胶pH值为4．34时,体系水解缩聚反应充分,所得荧光粉的光致发光强度最强;煅烧气氛显著影响荧光粉的发光强度,前驱体在N2（90％）＋H2（10％）的还原气氛下煅烧得到的发光粉发光强度最强;最佳热处理温度为900℃。     

溶胶-凝胶法制备Zn2SiO4:Eu3+红色荧光粉

采用溶胶-凝胶法在Zn2SiO4基质中掺杂Eu3+,合成了红色荧光粉Zn2SiO4:Eu3+.通过样品的X射线衍射光谱、红外光谱、扫描电镜以及光致发光光谱的测试和表征,研究了Zn2SiO4:Eu3+的内部结构和发光特性.扣描电镜结果显示样品为球状荧光粉,颗粒直径为1～3μm.在395 nm激发下,样品在613 nm处发射出很强的红光.结合荧光光谱,分析了样品的退火温度,Eu3+的浓度,电荷补偿剂Li+的浓度对样品发光强度的影响.研究发现,红色荧光粉Zn2SiO4:Eu3+的发光强度随退火温度的升高而增加,发光强度随Eu3+和Li+浓度的增加先增大后减小.     

Enhanced hyperthermia performance in hard-soft magnetic mixed Zn0.5CoxFe2.5−xO4/SiO2 composite magnetic nanoparticles

High quality Zn0.5CoxFe2.5?xO4(x=0,0.05,0.1,0.15)serial magnetic nanoparticles with single cubic structures were prepared by the modified thermal decomposition method,and Zn0.5CoxFe2.5?xO4/SiO2 composite magnetic nanoparticles were prepared by surface modification of SiO2.The magnetic anisotropy of the sample increases with the increase of the doping amount of Co2+.When the doping amount is 0.1,the sample shows the transition from superparamagnetism to ferrimagnetism at room temperature.In the Zn0.5CoxFe2.5?xO4/SiO2 serial samples,the maximum value of specific loss power(SLP)with 1974 W/gmetal can also be found at doping amount of x=0.1.The composite nanoparticles are expected to be an excellent candidate for clinical magnetic hyperthermia.     

Zn2SiO4(ZnB2O4):Mn2+,Sm3+发光材料的制备与荧光性能

使用高温固相法首次合成了Zn2SiO4(ZnB2O4):Mn2+,Sm3+发光材料,探讨了烧结温度、Sm2+含量对样品荧光性能的影响.利用X射线衍射(XRD)、荧光光谱等分析手段对Zn2SiO4(ZnB2O4):Mn2+,Sm3+粉末的结构、发光性能进行了表征.确定了该荧光材料的最佳合成条件,离子掺杂浓度等.实验结果表...     

Preparation and characterizations of SiO2/TiO2/γ-glycidoxypropyltrimethoxysilane composite materials for optical waveguides

SiO₂/TiO₂/γ-glycidoxypropyltrimethoxysilane composite materials processed by the sol-gel technique were studied for optical waveguide applications. Waveguide films with thickness more than 1.7 μm were prepared on a silicon substrate by a single-coating process and low-temperature heat treatment from these high-titanium-content composite materials. Scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-VIS), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) have been used to characterize the waveguide films. TGA curves showed that organic compounds in the composite materials would decompose in the temperature range from 200 °C to 480 °C. SEM, AFM and UV-VIS results showed that a dense, porous-free, and high transparency in the visible range waveguide film could be obtained at a low heat-treatment temperature. It was also noted that the carbon content in the film with higher titanium content heated at high temperature was evidenced by XPS. The waveguide propagation loss properties of the composite material films were also investigated and showed a dependence on the titanium molar fraction. Received: 13 June 2000 / Accepted: 21 June 2000 / Published online: 20 September 2000     

Permittivity and conductivity of triglycine sulfate films on Al/SiO2 and α-Al2O3 substrates

Triglycine sulfate (TGS) films have been prepared by evaporation from a saturated aqueous solution on substrates of fused quartz coated by a layer of thermally deposited aluminum (Al/SiO₂) and white sapphire (α-Al₂O₃) on whose surface interdigital electrodes have been deposited by photolithography. The TGS films have a polycrystalline structure made up of blocks measuring 0.1–0.3 mm (Al/SiO₂) and 0.1 × 1.0 mm (α-Al₂O₃). The polar axis in the blocks is mostly confined to the substrate plane. The temperature dependences of the capacitance and dielectric losses normal to and in the film plane have maxima at the temperature coinciding with that of the ferroelectric phase transition in a bulk crystal, T _c . The low-frequency conductivity G in TGS/Al/SiO₂ structures displays a frequency dispersion described by the relation G ∼ ω ^s (s ≈ 0.82). The conduction can be tentatively ascribed to the hopping mechanism involving localized carriers with a ground state energy of 0.8–0.9 eV. At temperatures above and below T _c , the low-frequency conductivity in TGS/α-Al₂O₃ films operates through a thermally-activated mechanism with an activation energy of 0.9–1.0 eV. At the phase transition, an additional contribution to conductivity appears in TGS/α-Al₂O₃ films with a dispersion G ∼ ω^0.5, which can be associated with domain-wall relaxation.     

Zn掺杂La2CuO4热电势和磁化率研究

测量了La2CuO4掺Zn样品在不同降温速率下(330K保温05h,然后分别以6Kh,02Ks的速度降到8K)的直流磁化率和热电势.实验结果表明,反铁磁温度TN不随降温速率变化而变化,其直流磁化率也未受很大影响.高温热电势弱的温度依赖关系表明为极化子气体的贡献.热电势在转折温度Tdrop之下的快速降低是由于二维反铁磁涨落的贡献.热电势在更低温度的拐点TS与载流子的局域化有关.降温速率变化时,Tdrop和TS都有明显的变化.Zn掺杂对Tdrop和TS没有明显影响,但导致了更强的载流子局域化.讨论了上述现象产生的物理图像 关键词： La2CuO4 直流磁化率 热电势     

A comparative study of electroluminescence from Ge／SiO2 and Si／SiO2 films

Ge/SiO_2 and Si/SiO_2 films were deposited using the two-target alternation magnetron sputtering technique. The Au/Ge/SiO_2/p-Si and Au/Si/SiO_2/p-Si structures were fabricated and their electroluminescence (EL) characteristics were comparatively studied. Both Au/Ge/SiO_2/p-Si and Au/Si/SiO_2/p-Si structures have rectifying property. All the EL spectra from the two types of the structure have peak positions around 650－660 nm. The EL mechanisms of the structures are discussed.