B4C作碳源高压合成金刚石的EPR谱特性

与传统用石墨作碳源不同，首次用Ｂ４Ｃ作碳源，在高温高压与过渡金属合金触媒作用下，合成出高含硼黑色金刚石。这种金刚石的ＥＰＲ谱不再具有由孤立替位氮引起的三共振峰，而是一条线宽为７×１０－４特斯拉、ｇ＝２．００２３、浓度约为２×１０１８自旋数／厘米３的罗伦兹型单峰。分析表明：这可能是金刚石中硼杂质引起的受主中心，抵消了氮原子的未偶电子顺磁性后，所产生的共振现象。由于Ｂ４Ｃ分离出碳原子少，金刚石生长速度较慢，金刚石中铁磁杂质含量低，因此，它们引起的共振现象不明显。     

氮掺杂金刚石{100}晶面的缺陷发光特性

氮是金刚石中最常见的杂质之一, 其对金刚石的缺陷发光具有重要的影响. 氮可以与金刚石中的本征缺陷形成复合缺陷. 本文首先利用阴极射线发光照片(CL)对一个高温高压合成的氮掺杂金刚石进行表征, 发现{100}晶面为蓝色, 然后利用透射电子显微镜(TEM)对该晶面进行电子辐照及后续退火处理, 以引入本征点缺陷进而形成含氮的复合缺陷, 并利用低温光致发光光谱(PL光谱)表征其缺陷发光特性, 发现该晶面主要以氮-空位复合缺陷(NV中心)发光为主, 并伴随着较弱的503 nm发光. 关键词： 金刚石 缺陷 发光     

氮氢共掺杂金刚石中氢的典型红外特征峰的表征

所有天然Ia型金刚石红外光谱中都存在3107 cm-1特征峰,而在金属触媒直接合成的金刚石红外光谱中没有检测出3107 cm-1特征峰.本文在6.3 GPa,1500?C条件下,通过Fe70Ni30触媒中添加P3N5直接合成出具有3107 cm-1特征峰的氮氢共掺杂的金刚石.红外光谱分析表明,合成的金刚石中氢有两种存在形式:一种对应着乙烯基团C=CH2中C—H键的伸缩振动(3107 cm-1)和弯曲振动(1450 cm-1)的吸收峰,另一种对应着sp3杂化C—H键的对称伸缩振动(2850 cm-1)和反对称伸缩振动(2920 cm-1)的吸收峰.通过分析发现,3107 cm-1吸收峰与金刚石中聚集态的氮原子有关,当金刚石中没有聚集态的氮元素时,即使氮含量高也不会出现3107 cm-1峰;并且2850和2920 cm-1附近的吸收峰比3107 cm-1附近的吸收峰更为普遍存在.这说明sp3杂化C—H键比乙烯基团的C—H键更广泛存在于金刚石中,从两者的峰值看,天然金刚石中的氢杂质主要以乙烯基团C=CH2存在.3107 cm-1吸收峰与聚集态的氮原子的这种存在关系为天然金刚石形成机制的研究提供了一种新思路,同时较低的合成条件也可能为氢与其他元素共掺杂合成具有n型半导体特性的金刚石提供一个较理想的合成环境.     

纯铁触媒合成磨料级金刚石及表征

本文报道了高温高压下纯铁触媒与石墨体系合成磨料级金刚石的过程,并给出了P-T相图.在此基础上,通过调整工艺参数,控制再结晶石墨量与金刚石生长速度,合成出无色透明的金刚石样品,解决了纯铁触媒合成的金刚石透明度较差及包裹体较多的问题.采用穆斯堡尔谱仪和傅里叶红外光谱仪等测试手段,对金刚石样品内部包裹体以及氮元素含量进行了表征,在揭示包裹体形成机理的基础上提出了减少包裹体的方法,同时阐明了纯铁触媒合成的金刚石样品颜色变浅的原因. 关键词： 铁触媒 金刚石 生长速度 高温高压     

稀土掺杂碱土金属硫化物晶体中的载流子俘获中心

研究了典型红外激励发光材料XS:Ra,Sm(X=Sr,Ca;Ra=Ce,Eu)的激励发光过程中电子与空穴的俘获中心及其转移过程,通过激发前后的红外吸收光谱的差异及吸收差与光激励谱的细微结构说明,电子俘获中心并不是Sm³⁺离子,但与Sm³⁺离子处于相邻的空间位置关系,Sm³⁺离子在载流子俘获与复合的过程中也没有发生价态或数量的变化,进一步的EPR谱研究表明Eu²⁺离子的价态在激发前后也没有发生变化。与共价性强的Ⅲ-Ⅴ族半导体晶体不同的是,在这类离子性较强的晶体中,载流子被杂质所引起的晶格缺陷而非杂质本身俘获。在多种发光中心的情况下,不同的激发波长可以使空穴束缚在不同的发光中心附近,随后产生不同的光激励发光。     

掺杂金刚石薄膜的缺陷研究

利用多普勒增宽谱和电子顺磁共振研究了掺硼和掺硫金刚石薄膜的缺陷状态.多普勒增宽谱的结果表明，不同杂质元素掺杂的金刚石薄膜，其中使正电子湮没的缺陷种类是相同的；正电子与不同杂质元素硼、硫之间的相互作用不明显；少量硼可使金刚石膜中的空位浓度减少.EPR结果表明，各掺杂样品的顺磁信号主要来自于金刚石的碳悬键. 关键词： 金刚石 掺杂 多普勒增宽谱 电子顺磁共振     

锌磷酸盐玻璃掺杂VO~(2+)吸收光谱和EPR谱研究

3d1离子(如VO2+,V4+)是一类非常重要的离子,其掺杂电子顺磁共振谱已有大量的研究,积累了丰富的实验数据。利用3d1离子在四角压缩八面体对称中EPR参量的高阶微扰公式,计算了锌磷酸盐玻璃晶体中掺杂VO2+的EPR参量(g因子g‖,g⊥和超精细结构常数A‖,A⊥)和光吸收谱。由于锌磷酸盐玻璃晶体中掺杂VO2+中配体O2-的自旋-轨道耦合参量ζ0p(≈150cm-1)与中心过渡金属3d1离子V4+的ζ0d(≈248cm-1)相差不太大,故来自配体的自旋-轨道耦合参量ζ0p对EPR参量和光吸收谱的贡献必须予以考虑。采用重叠模型建立了杂质中心结构参数与电子顺磁共振(EPR)参量以及光吸收谱之间的定量关系;通过拟合锌磷酸盐玻璃中V4+中心的EPR参量和光吸收谱理论与试验符合,获得了杂质中心[VO6]8-基团的局域结构;研究发现,[VO6]8-基团的平行和垂直于C4轴的键长分别为:R‖≈0.175nm,R⊥≈0.197nm,即[VO6]8-基团的局域结构为沿C4轴方向呈压缩的八面体结构;所得EPR参量和光吸收谱的理论值与实验符合很好,并对上述结果的合理性进行了讨论。这说明微扰法可以用来研究材料中掺杂3d1过渡金属离子的EPR参量和光吸收谱。此外,对超精细结构常数(A‖和A⊥)的研究发现,较大的芯区极化常数κ值说明VO2+中未配对的s电子对超精细结构常数有较大的贡献。     

高含硼金刚石的一阶Raman谱特性分析

对B4C为碳源、分别以FeNiCo与NiMnCo合金为触媒,高温高压下合成出的高含硼金刚石(B含量大于1wt%),进行了拉曼谱测试。实验表明:这类金刚石的室温一阶拉曼谱线位移分别为1324cm-1与1320cm-1,半峰宽(FWHM)分别为22cm-1及28cm-1。对比不同含硼量金刚石的拉曼谱发现,随着硼含量增加,拉曼位移的红移量增加,线宽加宽,峰值下降。这与硼杂质原子进入金刚石,造成晶格畸变与缺陷有关     

氮对金刚石缺陷发光的影响

利用低温显微荧光光谱研究了IIa型、Ib型、Ia型金刚石的缺陷发光性质. 研究发现, 随着氮含量增加, 间隙原子及空位逐渐被氮原子所束缚, 从而使得GR1中心、533.5 nm及580 nm中心等本征缺陷发光减弱, 而氮-空位复合缺陷(NV中心)及523.7 nm中心等氮相关缺陷发光增强. 高温退火后, 间隙原子与空位可以自由移动, IIa型金刚石中出现了NV⁰中心, Ib型金刚石中只剩下了NV中心, Ia型金刚石中氮原子之间发生团聚, 出现了H3中心及N3中心. 另外, 氮作为施主原子, 有利于负电荷缺陷的形成, 如3H 中心、NV^- 中心.     

扬子克拉通西部金刚石的表面形貌特征及其振动光谱研究

基于金刚石表面形貌的研究,有可能为反演金刚石的形成环境及为金刚石的合成工艺设计提供科学线索。采用光学显微镜、红外光谱、拉曼光谱对扬子克拉通西部的天然砂矿金刚石表面形貌与杂质氮、氢含量及有序度的关系研究结果表明,金刚石的表面形貌包括与晶体生长相关的微形貌、与晶体定向相关的熔蚀形貌、与晶体定向无关的熔蚀形貌及与应力形变相关的形貌等四大类;金刚石以IaAB型为主,氮含量介于22.90～752.40 μg·g-1之间,绝大部分样品的sp3杂化C-H键浓度含量高于sp2杂化C-H键,氢杂质的存在有利于A氮心向B氮心转变;sp3杂质C-H键的存在对金刚石表面出现的形貌类型可能不会造成实质性的影响,但极利于形成熔蚀坑;各种表面形貌的存在都会降低金刚石的表面有序度,但发育晕线者的表面有序度相对最高,而发育三角形生长片层者表面有序度最低。     

Inverted EPR signal from nitrogen defects in a synthetic diamond single crystal at room temperature

Electron paramagnetic resonance (EPR) in diamond single crystals was studied. The crystals were grown using apparatuses of the “split-sphere” type in a Ni-Fe-C system using the temperature gradient method with a subsequent high-temperature high-pressure treatment. It was found that, after the high-temperature high-pressure treatment of a diamond sample, the EPR signal from the lattice defects containing nitrogen atoms became inverted with the growth of the microwave power in an H₁₀₂ resonator. In a constant polarizing magnetic field, when the microwave power applied to the diamond was low, a resonance absorption by the nitrogen defects took place, whereas, when the microwave power was high, an emission was observed. The inversion of the EPR lines of a single nitrogen atom substituting for a carbon atom at a diamond lattice site could be caused by the presence of a nickel atom with an uncompensated magnetic moment at the adjacent tetrahedral interstitial site. In synthetic diamond crystals that were not subjected to high-temperature high-pressure treatment, the inversion of the EPR signal from nitrogen atoms (P1 centers, nitrogen in the C form) was absent.     

EPR study of the peculiarities of incorporating transition metal ions into the diamond structure

In this paper previously obtained data is reviewed and new data is discussed about nickel-containing centers in diamonds. These data are used to suggest interpretation of new data about cobalt-containing centers and to understand the influence of iron on the defects in diamonds grown in the iron system. A newly discovered nickel-nitrogen center has three nitrogen atoms in the first neighbor sphere around the double semi-vacancy and looks like the N3 (P2) center. In diamonds grown in the cobalt system two new types of cobalt-containing centers were found (NLO2 and NWO1). Both centers have electron spinS=1/2 and hyperfine structure from one cobalt ion (I=7/2 with natural abundance 100%). A case can be made for a double semi-vacancy structure for these defects. Special growth of diamond in the system enriched in¹⁵N decreased the line width down to 0.6 G, but gave no direct evidence of the existence of nitrogen in the defect structure. Asymmetrical shapes of the lines in the electron paramagnetic resonance (EPR) spectra of cobalt-containing centers with opposite signs in low and high magnetic field parts of spectra are due to very sensitive spin-Hamiltonian parameters of these defects to the lattice distortions. Annealing of cobalt-containing crystals at 2600 K produces the disappearance of all cobalt-containing EPR spectra, probably due to the capture of an additional nitrogen atom and the creation of a 3d⁶ diamagnetic state. In diamonds grown in the iron system with a high content of nitrogen there is evidence of an influence of ferromagnetic inclusion on the exchange interaction between substitutional nitrogen as an additional channel of indirect exchange interaction.     

13C spin-lattice relaxation in natural diamond: Zeeman relaxation in fields of 500 to 5000 G at 300 K due to fixed paramagnetic nitrogen defects

¹³C Spin–lattice relaxation (SLR) times in the laboratory frame have been measured at room temperature as a function of field in the range of 500 to 5000 G on two natural type Ib and Ia diamonds after dynamic nuclear polarization. Each of the diamonds contains two types of fixed paramagnetic centers with overlapping inhomogeneous electron paramagnetic resonance (EPR) lines. EPR techniques have been employed to identify these defects and to determine their concentrations and relaxation times at X-band. Three different nuclear SLR paths, namely that due to electron SLR and two types of three spin processes, are discussed. The one three-spin process (TSP) (type 1) involves a simultaneous transition of two electron spins belonging to the same hyperfine EPR line and a ¹³C spin while the other process (type 2) involves two electron spins belonging to different hyperfine EPR lines and a ¹³C spin. It is shown that the thermal contact between the ¹³C nuclear Zeeman and electron dipole–dipole interaction reservoirs decreases with an increase in field intensity, thus forming a bottleneck in the ¹³C relaxation path due to the type 1 TSP. The contribution of TSP of type 1 dominates that due to electron SLR and the type 2 TSP in relaxing the ¹³C nuclei in type Ib diamond from about 1200 to 5000 G, while for type Ia diamond it dominates from 500 up to about 2200 G. In type Ia diamond over the range 2200 to 5000 G it seems that the type 2 TSP, which involves electrons of neighboring P2 hyperfine lines, dominates that of electron spin–lattice and the type 1 TSP. Over the range 500 to about 1200 G, a field-dependent electron SLR mechanism associated with N3 centers appears to dominate the ¹³C SLR.     

Interpretation of perturbed angular distribution results for19F implanted into diamond

Perturbed Angular Distribution measurements have been made on natural diamond using recoil implanted fluorine ions as probes. Two distinct lattice sites for fluorine in diamond were found. Site identifications prompted by theoretical cluster calculations are presented. The PAD data are well described by a texture theory, though the origin of the texture effects is presently not known.     

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr²⁺, Co²⁺, or Fe²⁺), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn²⁺, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.     

EPR and IR spectral studies on Mn ions in nickel maleate tetrahydrate single crystals

Electron paramagnetic resonance (EPR) studies have been carried out on Mn²⁺ ions doped in nickel maleate tetrahydrate single crystals in the temperature range 103-413 K on X-band frequency. The EPR spectrum at room temperature exhibits a group of five fine structure transitions each splits into six hyperfine components. Angular variation studies reveal the presence of a single site and it is found that Mn²⁺ ions enter the lattice substitutionally. From the observed EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The variation of zero-field splitting parameter (D) with temperature is measured. The observed EPR spectra exhibit a large anisotropy in the widths of Mn²⁺ resonance lines. The widths of Mn²⁺ resonance lines increase with the Zeeman field intensity and these observations have been discussed in detail. The infrared spectrum exhibits bands characteristic of the carboxylic acid salts.     

High-frequency (94.9 GHz) EPR spectroscopy of paramagnetic centers in a neutron-irradiated sapphire single-crystal fiber

Initial results are reported of an EPR study, conducted at 94.9 GHz, of a thermally annealed, neutron-irradiated white sapphire (α-Al₂O₃) single-crystal fiber. The optical centers produced in sapphire by neutron irradiation and thermal annealing are of interest for optical technologies involving the phenomenon of spectral hole-burning. While these centers have been modeled as consisting of electrons localized at anion vacancies, experimental tests of this model have been very limited. EPR spectroscopy — a choice technique for elucidating structural details of such color centers — reveals signals from numerous paramagnetic centers in this material. The predominant signals, with amplitudes a hundredfold greater than any other signals, derive from three closely related, highspin-multiplicity centers. These centers do not, however, derive from radiation-induced lattice defects: they are readily identified as Cr³⁺ (S = 3/2) and a pair of crystallographically equivalent Fe³⁺ (S=5/2) impurity ions. The advantages of high-frequency-EPR instrumentation in facilitating this identification are presented and discussed in detail. These advantages include enhanced sensitivity for this volume-limited, fiber sample. Moreover, the analysis of the spectra — entailing spectral assignments, evaluation of the spin-Hamiltonian parameters, and spin-counting — is greatly facilitated when the Zeeman interaction is dominant.     

EPR and optical spectroscopy of Yb<Superscript>3+</Superscript> ions in CaF<Subscript>2</Subscript>: an analysis of the structure of tetragonal centers

CaF₂ crystals doped with Yb³⁺ ions have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy. EPR spectra of paramagnetic centers (PCs) for cubic (T_c) and tetragonal (T_tet) symmetries were identified. Empirical energy level diagrams were established and crystal field parameters were determined. Information on the CaF₂∶Yb³⁺ phonon spectra was obtained from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyze the crystal lattice distortions in the vicinity of the Yb³⁺ ion. Within the framework of a superposition model, it is established that four F⁻ ions located symmetrically with respect to the fourfold axis from the side of the ion-compensator approach the impurity ion and deviate from the PC axis. The second set of four fluorine ions also approaches the Yb³⁺ ion and the PC axis. The ion-compensator F⁻ also approaches considerably the impurity ion.     

EPR Studies of DOPA–Melanin Complexes with Fe(III)

Paramagnetic centers in 3,4-dihydroxyphenylalanine–melanin and its complexes with Fe(III) were examined by electron paramagnetic resonance (EPR) spectroscopy. Paramagnetic centers of melanin play an important role in detoxification of environment and they reveal high activity in binding of metal ions. Two different signals were observed in EPR spectra: lines of o-semiquinone free radicals and lines of paramagnetic Fe(III). Amplitudes of EPR lines of both free radicals and iron ions decrease with increasing Fe(III) content in melanin–metal ion complexes. Free radical concentrations in the melanin samples, g-factors, amplitudes and line widths of EPR spectra were determined. It was stated that fast spin–lattice relaxation processes exist in both free radical system and paramagnetic iron ions in melanin complexes.     

EPR and optical absorption spectra of VO2+ ions in calcium oxalate monohydrate single crystals

Abstract

Electron paramagnetic resonance (EPR) and Optical absorption spectra of vanadyl ions in calcium oxalate monohydrate single crystals have been studied. EPR spectrum at room temperature exhibits an isotropic octet spectrum. The detailed EPR analysis indicates that vanadyl ions exhibit liquid like behaviour. EPR spectrum has been studied at different temperatures. It is found that at 255 K, the EPR spectrum completely disappears. The optical absorption spectrum exhibits three absorption bands characteristic of vanadyl ions in tetragonal symmetry. From the optical data, the crystal field and tetragonal parameters have been evaluated.