共查询到20条相似文献,搜索用时 140 毫秒
1.
2.
本文采用基于密度泛函理论的第一性原理平面波赝势和局域密度近似方法,优化了立方和六方氮化硼的几何结构,系统地研究了零温高压下立方和六方氮化硼的几何结构、力学、电学以及光学性质.结构与力学性质研究表明:立方氮化硼的结构更加稳定,两种结构的氮化硼均表现出一定的脆性,而六方氮化硼的热稳定性则相对较差;电学性质研究表明:立方氮化硼和六方氮化硼均为间接带隙半导体,且立方氮化硼比六方氮化硼局域性更强;光学性质结果显示:立方氮化硼和六方氮化硼对入射光的通过性都很好,在高能区立方氮化硼对入射光的表现更加敏感.此外,还研究了高温高压下立方氮化硼的热力学性质,并得到其热膨胀系数、热容、德拜温度和格林艾森系数随温度和压力的变化关系.本文的理论研究阐述了高压下立方氮化硼和六方氮化硼的相关性质,为今后的实验研究提供了比较可靠的理论依据. 相似文献
3.
4.
文内报告了尺寸为0.3×0.3 mm2的立方氮化硼单晶的N-型掺杂,然后 用特殊的测量装置测量了N-型立方氮化硼的欧姆接触之后的伏-安特性。 相似文献
5.
较系统地研究了不同衬底材料对制备氮化硼薄膜的影响。用热丝增强射频等离子体CVD法,以NH3,B2H6和H2为反应气体,在Si,Ni,Co和不锈钢等衬底材料上,成功生长出高质量的立方氮化硼薄膜,还用13.56MHz的射频溅射系统将c-BN薄膜沉积在Si衬底上,靶材为h-BN(纯度为99.99%),溅射气体为氩气和氮气的混合气体,所得到的氮化硼薄膜中立方相含量高于90%,用X射线衍射谱和傅里叶变换红谱对样品进行了分析表明,衬底材料与c-BN的晶格匹配情况,对于CVD生长立方氮化硼薄膜影响很大,而对溅射生长立方氮化硼薄膜影响不大。 相似文献
6.
7.
8.
在AISI 4140基体上采用预置材料激光熔敷的方法制备了镍石墨烯立方氮化硼(Ni-Graphene-CBN)复合材料涂层。X射线衍射(XRD)和Raman测试证明了石墨烯和CBN存在于所制备的涂层材料中。扫描电镜(SEM)图片给出了所制备的复合材料涂层的表面和断面形貌。进行了复合材料涂层的纳米机械性能和耐磨性的测试。测试结果表明:随着CBN含量的增加,复合涂层的硬度及弹性模量相应提高,分别由4.3 GPa提高到6.2 GPa和101 GPa提高到140 GPa; 同时其耐磨性也有明显改善,6% CBN含量的涂层摩擦系数由基体材料的0.2降低到0.15,最大磨损量降到基体磨损量的一半。 相似文献
9.
10.
11.
Hydrodynamic cavitation in a Venturi tube produces luminescence, and the luminescence intensity reaches a maximum at a certain cavitation number, which is defined by upstream pressure, downstream pressure, and vapor pressure. The luminescence intensity of hydrodynamic cavitation can be enhanced by optimizing the downstream pressure at a constant upstream pressure condition. However, the reason why the luminescence intensity increases and then decreases with an increase in the downstream pressure remains unclear. In the present study, to clarify the mechanism of the change in the luminescence intensity with cavitation number, the luminescence produced by the hydrodynamic cavitation in a Venturi tube was measured, and the hydrodynamic cavitation was precisely observed using high-speed photography. The sound velocity in the cavitating flow field, which affects the aggressive intensity of the cavitation, was evaluated. The collapse of vortex cavitation was found to be closely related to the luminescence intensity of the hydrodynamic cavitation. A method to estimate the luminescence intensity of the hydrodynamic cavitation considering the sound velocity was developed, and it was demonstrated that the estimated luminescence intensity agrees well with the measured luminescence intensity. 相似文献
12.
13.
Up-conversion luminescence tuning in Er~(3+) -doped ceramic glass by femtosecond laser pulse at different laser powers 下载免费PDF全文
《中国物理 B》2018,(12)
The up-conversion luminescence tuning of rare-earth ions is an important research topic for understanding luminescence mechanisms and promoting related applications. In this paper, we experimentally study the up-conversion luminescence tuning of Er~(3+)-doped ceramic glass excited by the unshaped, V-shaped and cosine-shaped femtosecond laser field with different laser powers. The results show that green and red up-conversion luminescence can be effectively tuned by varying the power or spectral phase of the femtosecond laser field. We further analyze the up-conversion luminescence tuning mechanism by considering different excitation processes, including single-photon absorption(SPA), two-photon absorption(TPA), excited state absorption(ESA), and energy transfer up-conversion(ETU). The relative weight of TPA in the whole excitation process can increase with the increase of the laser power, thereby enhancing the intensity ratio between green and red luminescence(I_(547)/I_(656)). However, the second ETU(ETU2) process can generate red luminescence and reduce the green and red luminescence intensity ratio I_(547)/I_(656), while the third ESA(ESA3) process can produce green luminescence and enhance its control efficiency. Moreover, the up-conversion luminescence tuning mechanism is further validated by observing the up-conversion luminescence intensity, depending on the laser power and the down-conversion luminescence spectrum under the excitation of 400-nm femtosecond laser pulse. These studies can present a clear physical picture that enables us to understand the up-conversion luminescence tuning mechanism in rare-earth ions, and can also provide an opportunity to tune up-conversion luminescence to promote its related applications. 相似文献
14.
Influences of Mg^2+ ion on dopant occupancy and upconversion luminescence of Ho^3+ ion in LiNbO3 crystal 下载免费PDF全文
The effects of a Mg^2+ ion on the dopant occupancy and upconversion luminescence of a Ho^3+ ion in LiNbO3 crystal are reported. The birefringence gradient of the crystal is measured to investigate the optical homogeneity. The X-ray powder diffraction spectrum and the upconversion luminescence are used to investigate defect structure and spectroscopic properties of Mg,Ho:LiNbO3. Under 808-nm excitation, blue, red, and very intense yellow-green bands are observed. Based on the energy levels of Ho^3+ in LiNbO3, and the pump intensity dependence of the observed emission, an excitation scheme is presented. The upconversion emission spectra reveal an enhancement of upconversion intensity when the Mg^2+ ions are introduced into Ho:LiNbO3. The main upconversion mechanism is discussed in this work. 相似文献
15.
XU Yan-Ling WANG Rui WANG Bin-Ju LIU Wei-Hai WANG Jia WANG Miao YANG Tong-Yong 《中国物理快报》2008,25(6):2246-2248
Zn and RE (RE=La, Yb, Y) ions co-doped PbWO4 (PWO) single crystal grown by the Czochralski technique are characterized by x-ray diffraction (XRD), opticaltransmission spectra, and photoluminescence (PL). The doping of Zn ions shows distinct effects on the properties of PWO:RE crystals. At low concentration of Zn ions (200ppm), the luminescence intensity is quite weak for (Zn,La)-doped PWO, but is substantially strong for (Zn,Yb)-doped PWO. The blue luminescence intensity is significantly enhanced with the increasing Zn ions doping for PWO:Y. The trivalent ions codoping can increase the ratio of the blue luminescence contributing to the fast components of light yield. Ybions can enhance efficiency of luminescence in PWO:Yb:Zn because they may act as a luminous sensitization agent which can be involved in the efficient energy transfer and storage of the radiative process. 相似文献
16.
理论研究了648nm激光抽运掺Tm晶体的可见与红外发光转换和发光双稳特性.根据系统的耦合速率方程理论,推导了发光转换阈值的解析表达式,数值研究了Tm3+能级布居数,辐射光谱以及发光强度等随抽运光强的变化.数值结果表明,648nm激光抽运下可以实现452/469nm蓝光与1716 nm红外光谱的发光转换.在光子雪崩阈值附近,可以观察到掺Tm晶体的辐射光谱双稳,荧光色度双稳和发光强度双稳等现象.利用掺Tm晶体的可见与红外发光转换与双稳特性,可以实现抽运功率控制的全固态发光转换器和双稳波长
关键词:
光学双稳
多色开关
掺Tm晶体
光子雪崩 相似文献
17.
纳秒脉冲激光诱导土壤等离子体辐射强度研究 总被引:1,自引:0,他引:1
为了改善激光诱导击穿光谱质量,采用Nd∶YAG激光器输出的纳秒脉冲激光激发土壤样品,由光栅光谱仪和光电检测系统记录激光诱导等离子体发射光谱,研究了激光输出能量(100~500mJ)对等离子体辐射强度的影响。实验结果表明,在激光能量为200mJ的优化条件下,可以提高光谱强度和信背比。当激光束被适当散焦以后激发样品时,能够进一步改善光谱质量,散焦位置为+6mm时元素Mg,Al,K和Fe的谱线强度比未散焦时分别提高了46%,63%,59%和45%,而光谱信背比分别提高了11%,31%,35%和38%。这为检测土壤样品中痕量杂质元素奠定了基础。 相似文献
18.
Ch. B. Lushchik F. A. Savikhin V. N. Makhov O. V. Ryabukhin V. Yu. Ivanov A. V. Kruzhalov F. G. Neshov 《Physics of the Solid State》2000,42(6):1052-1057
At high excitation densities, recombination-assisted creation of cation excitons, which transfer energy efficiently to the anion sublattice to initiate the luminescence of anion excitons and impurity centers, has been observed in CsCl crystals. At the same time, the creation of cation excitons competes with the electron recombination with cation holes and quenches the cross-luminescence. The intensity ratio of the cross-luminescence to exciton-impurity luminescence is different for crystal irradiation with γ rays and heavy particles. 相似文献
19.
Collinear dual-pulse laser-induced breakdown spectroscopy was carried out on Si crystal by using a pair of nanosecond Nd:YAG laser sources emitting at 1064 nm. The spectral intensities and signalto-noise ratios of selected Si atomic and ionic lines were used to evaluate the optical emission. The optical emission intensity was recorded while varying the interpulse delay time and energy ratio of the two pulsed lasers. The effects of the data acquisition delay time on the line intensity and signal-to-noise ratio have been investigated as well. Based on the results, the optimal interpulse delay time, energy ratio of the two pulsed lasers, and data acquisition delay time for achieving the maximum atomic and ionic line intensities were found for generation of Si plasma with the collinear dual-pulse laser approach. The dominant mechanism for the observed line intensity variation was also discussed. In addition, the plasma temperature and electron number density at different gate delay times and different interpulse delay times were derived. A significant influence of plasma shielding on the electron temperature and electron number density at shorter interpulse delay times was observed. 相似文献
20.
本文采用垂直Bridgman法,分别生长了未掺杂LaCl3和掺有不同浓度CeCl3的LaCl3闪烁晶体,并对它们的透光性质、发光性质和光衰减特性进行了测试和对比分析.发现未掺杂LaCl3晶体的吸收边位于215 nm附近,本征发射峰为405 nm,衰减时间在1μs以上.该发光属于纯氯化镧晶体的自陷激子发射,但随着CeCl3掺杂浓度的提高,源于自陷激子(STE)的本征发射强度逐渐降低,LaCl3:Ce晶体中的吸收边逐渐红移至300nm,由Ce3+中心所产生的5d→4f发射逐渐增强,其衰减时间加快至~20 ns.这种现象被解释为LaCl3晶格中的自陷激子向Ce3+离子发光中心的能量传递作用所致. 相似文献