共查询到20条相似文献,搜索用时 15 毫秒
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Bayley H 《Physics of life reviews》2012,9(2):161-3; discussion 174-6
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S. P. Gabuda A. S. Kolesnikov S. G. Kozlova N. K. Moroz 《Applied magnetic resonance》2011,41(2-4):431-437
The interaction between ammonium NH3 and H2O molecules in zeolitic nanopores is studied by in situ 1H nuclear magnetic resonance (NMR) method. The powder and single crystal samples of natural zeolites, heulandites Ca4[Al8Si28O72]·24H2O and clinoptilolite (Na, K,Ca1/2)6[Al6Si30O72], were used as the model system. It is shown that penetration of NH3 into the zeolitic nanopores is accompanied by disordering of the hydrogen sublattice of zeolitic water and by the fast proton exchange NH3 + H2O ? [NH4]+ + [OH]? characterized by correlation frequency v c = ~40 kHz. Another nanoreactor interactions are represented by interaction of [NH4]+ ions with exchangeable Na+ and Ca2+ ions of the zeolitic structure. The slow ionic exchange [NH4]+ → [Na,Ca1/2]+ and binding of [NH4]+ in cationic sites of the framework were visualized by NMR spectroscopy along with stepwise release of (Na,Ca1/2)OH from zeolitic pores to the external surface of zeolite grains. 相似文献
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分别测量了Er YCOB晶体和ErYb YCOB晶体的室温吸收光谱.讨论了Yb3+离子对Er3+离子的敏化作用. 相似文献
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为提高固体激光器的能量利用率,增大输出能量,将双掺Nd:Ce:YAG晶体的输出特性与普通Nd:YAG晶体进行了对比研究。分析了Nd3+和Ce3+的吸收光谱对激光晶体初始阈值反转粒子数的影响,结果显示:双掺Nd:Ce:YAG晶体可以提高晶体对泵浦光能量的利用率及激光器的输出能量,且可降低阈值泵浦能量。并分别检测了Nd:Ce:YAG激光晶体与Nd:YAG晶体的输出激光能量和阈值泵浦能量,实验结果表明:在输入电压为750 V时,Nd:Ce:YAG晶体与Nd:YAG晶体的输出能量分别为651.5 mJ 和390.4 mJ,能量利用率分别为2.31%和1.38%,激光振荡需要的泵浦能量阈值分别为10.56 mJ和15.21 mJ,且普通Nd:YAG晶体的斜效率为0.36%,而双掺Nd:Ce:YAG晶体的为0.49% 。 相似文献
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为提高固体激光器的能量利用率,增大输出能量,将双掺Nd:Ce:YAG晶体的输出特性与普通Nd:YAG晶体进行了对比研究。分析了Nd3+和Ce3+的吸收光谱对激光晶体初始阈值反转粒子数的影响,结果显示:双掺Nd:Ce:YAG晶体可以提高晶体对泵浦光能量的利用率及激光器的输出能量,且可降低阈值泵浦能量。并分别检测了Nd:Ce:YAG激光晶体与Nd:YAG晶体的输出激光能量和阈值泵浦能量,实验结果表明:在输入电压为750 V时,Nd:Ce:YAG晶体与Nd:YAG晶体的输出能量分别为651.5 mJ 和390.4 mJ,能量利用率分别为2.31%和1.38%,激光振荡需要的泵浦能量阈值分别为10.56 mJ和15.21 mJ,且普通Nd:YAG晶体的斜效率为0.36%,而双掺Nd:Ce:YAG晶体的为0.49% 。 相似文献
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S. Masilla Moses Kennedy 《Journal of luminescence》2008,128(4):680-684
The optical absorption (OA) and photoluminescence (hereafter referred to as luminescence) studies were made on CaF2:Dy:Pb:Na single crystals (Dy—0.005 at%, Pb—0.188 at% and Na—0.007 at%) before and after γ-irradiation. The unirradiated crystal exhibited a strong OA band around 6.36 eV attributed to the ‘A’ band absorption of Pb2+ ions. The γ-irradiated crystal exhibited OA bands around 2.06, 3.28, 3.75 (broad shoulder) and 2.48 eV. The first three bands could be tentatively attributed to MNa centre when compared with that of the coloured CaF2:Na. The origin of 2.48 eV band was not explicitly known. Luminescence emission and excitation of Pb2+ and Dy3+ ions were negligible in the unirradiated crystal. Irradiated crystal exhibited a strong excitation spectrum with overlapping bands, due to different colour centres, in the UV-vis region for the 2.15 eV emission characteristic of Dy3+ ion. When excited, the absorbed energy (may be a part) was transferred from a colour centre to nearby Dy3+ ions and Dy3+ characteristic emission was observed. Exciting the irradiated crystal around 3.28 eV yielded emission at 2.56, 2.15 and 1.76 eV. The first two emission bands were due to Dy3+ ions. The excitation spectrum for the 1.76 eV emission showed two prominent bands around 2.02 and 3.08 eV and hence the emission was attributed to the MNa centre. The luminescence mechanism was described. 相似文献
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我国著名物理学家王淦昌先生极为关心中学英才教育,多次与本刊主编探讨这一关系千秋大业的话题.他在年事已高、科研繁忙之时,还审阅了张大同先生的《论“英才教育”》一文,写下了极为重要的评语,这对搞好英才教育、培养栋梁之材有着积极作用。王淦昌先生审阅张大同先生此文的意见如下:“当此举国上下都在从事科技兴国的伟大事业时,很重要的一点:是要发现英才、培养英才,以为国家所用。兹介绍关于这方面有丰富经验因而有很大贡献的张大同同志(上海华东师范大学二附中物理学教师)的一篇文章。从这里可以得到启发,如何为国家培养出很多优秀的物理或其他学科的人才。” 相似文献
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B. Schuh 《Zeitschrift für Physik B Condensed Matter》1979,34(1):37-44
The periodics-d-model is investigated by Green function methods. We find that the lnT-divergence appearing in third order perturbation theory for the electron selfenergy is smoothed out but still shows up in a characteristic decrease (exchange coupling<0) or increase (>0) of lifetime of electrons at the fermi level asT0 and a corresponding structure in the specific heat. However, in contrast to the single impurity case, the corresponding characteristic temperature does not vary like exp[–1/||] but always is of order
2. From a mean field theory of the model, one finds a critical temperature for a transition into a magnetically ordered stateT
c0
which varies precisely like
2. Thus an interesting competition between Kondo-effect and long-range magnetic order can be expected in this model.Work performed within the research program of the SFB 125 Aachen/Jülich/Köln 相似文献
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用CH4,H2和NH3为反应气体,利用等离子体增强热丝化学气相沉积在沉积有碳膜的Si衬底上制备了a-C:N:H纳米尖端,并用扫描电子显微镜和微区Raman光谱仪对碳膜和纳米尖端进行了表征。结果表明:Raman谱中含有与碳和氮相关的峰,且纳米尖端的Raman谱比碳膜的Raman谱有很强的荧光背景。Raman谱中的峰说明沉积的碳膜和纳米尖端是a-C:N:H薄膜和a-C:N:H尖端。a-C:N:H纳米尖端的Raman谱中强荧光背景的产生表明其在激发光源照射的过程中发射了强荧光,对a-C:N:H纳米尖端产生强荧光的机理进行了探讨。 相似文献
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建立了包括扩散、漂移和光伏打效应三种输运机制,小信号光强、小调制度近似下描述双掺杂LiNbO3:Fe:Mn晶体用双色光进行全息存储的动力学的耦合微分方程组,数值求解并解释了晶体光存储的时间动态发展过程.在此基础上,分析了晶体的氧化还原程度对全息存储过程的影响,只有在晶体总的受主数密度Na(即Fe3+和Mn3+的数密度之和)大于铁离子数密度N2的条件下,双掺杂LiNbO3:Fe:Mn晶体全息存储才能达到非破坏性存储的目的.经过光固定的光栅的衍射效率随氧化增大,光折变灵敏度随氧化而减小,要获得高衍射效率就必须以降低光折变灵敏度为代价.在掺铁浓度一定的情况下,掺锰浓度越高,能实现信息长期存储对应的氧化还原状态的有效动态范围越大. 相似文献
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F. Cornacchia E. Sani A. Toncelli M. Tonelli M. Marano S. Taccheo G. Galzerano P. Laporta 《Applied physics. B, Lasers and optics》2002,75(8):817-822
Single crystals of monoclinic BaY2F8 and tetragonal LiYF4 codoped with the same Tm3+ and Ho3+ concentrations were successfully grown by the Czochralski method. Here we present a comparative analysis of the two hosts
including spectroscopic characterization and cw diode-pumped laser experiments in the 2-μm wavelength region at room temperature.
The main differences between the two hosts are a lower slope efficiency associated with a much wider tuning range (2005–2094 nm)
of BaY2F8 with respect to LiYF4.
Received: 29 July 2002 / Published online: 11 December 2002
RID="*"
ID="*"Corresponding author. Fax: +39-050/2214-333, E-mail: toncelli@df.unipi.it 相似文献
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LiNbO3:Cr:ZnO晶体生长和光谱特性的研究 总被引:3,自引:2,他引:1
采用提拉法从近化学计量比的熔体中生长出尺寸为φ20 mm×50 mm的优质LiNbO3:Cr:ZnO(CZLN)晶体,其光学均匀度为7.59(10-5).进行了吸收和荧光光谱的测定研究.吸收谱测试表明:Cr3 离子在晶体中有2个宽且强的吸收带及1个微弱的吸收线,两宽带中心波长分别为480和660 nm,对应于4A2→4T1和4A2→4T2两个具有相同的总自旋能级之间的跃迁,在4A2→4T2吸收宽带的长波边缘处有个很小的吸收峰,其波长为727nm,对应于4A2→2E(R线)的跃迁.荧光测试表明:当激发波长为660 nm时,CZLN晶体荧光宽带和1个较弱的荧光线峰并存,宽带范围为802~988 nm,峰值波长为871 nm,对应于4T2→2E,4A2的联合能级跃迁,荧光线峰波长约为754 nm,其强度较弱,相应于2E→4A2(零声子线)能级跃迁.计算了晶场强度和Racah参数,其Dq/B=2.72,晶体属于强场介质.研究表明,CZLN晶体具备可调谐激光晶体的基本光谱要求,且有良好的物化性能,可以实现宽频带可调谐激光输出.它又具有较大的倍频系数,有望实现420 nm附近紫外的自倍频激光输出. 相似文献