双掺(Tm3+,Tb3+)LiYF4激光器1.5 μm波长激光阈值分析

由速率方程推出了双掺（Tm^3 ,Tb^3 ）离子准四能级系统的激光阈值解析式，讨论了Tm^3 和Tb^3 离子之间的相互作用。分析了1.5μm波长附近的激光阈值和Tm^3 、Tb^3 离子的掺杂原子数分数及晶体长度的关系。结果表明，对于对应Tm^3 离子^3H4→^3F4跃迁的约1.5μm波长的激光，激活离子Tm^3 的掺杂原子数分数过大时，交叉弛豫作用将使系统阈值迅速增加。Tb^3 离子的加入，一方面能抽空激光下能级，起到降低阈值的作用；另一方面亦减少了激光上能级的寿命，使阈值升高。故Tb^3 离子有最佳掺杂原子数分数。对于Tm原子数分数为y=0.01的Tm:LiYF4晶体，Tb^3 离子的最佳掺杂原子数分数为0.002左右，同时表明，激光阈值与晶体长度有关。最佳晶体长度与Tm^3 、Tb^3 离子的掺杂原子数分数以及晶体的衍射损耗和吸收损耗有关。     

The growth and optical properties of ZnO nanowires at the junctions of nanowalls

Highly pure ZnO nanowires at the junctions of nanowalls have been successfully prepared via a simple vapor phase route at relative low temperature in the absence of catalyst. SEM, TEM, Raman scattering and PL were employed to characterize as-grown samples. The nanowires have average diameter of 10 nm with [001] growth direction. Raman scattering shifted from higher frequency to lower frequency and the enhancement of PL intensity of the green emission to the UV may be attributed to smaller nanowires and thinner nanowalls. This nanostructure may have important applications in batteries, light-emitting and energy conversion devices and other fields demanding high surface area materials.     

Multiferroic TbMnO3 nanoparticles

We report on the synthesis of TbMnO₃ nanoparticles by chemical co-precipitation route and their structural, chemical bonding, magnetic and dielectric properties. It is shown that the interesting multiferroic properties of this system as reflected by the concurrent occurrence of magnetic and dielectric transitions are retained in the nanoparticles (size∼40 nm). However, the nanoparticle constitution and properties are seen to depend significantly on the calcination temperature. While the nanoparticles obtained by calcination at 800 °C correspond very well with the reported properties of single phase TbMnO₃ (all the key magnetic and dielectric features near 7, 27 and 41 K, albeit with reduced dielectric constant) the nanoparticles obtained by calcination at 900 °C develop a Tb deficient skin which softens the transitions, reducing the dielectric constant further.     

水热合成稀土氟化物材料YLiF4∶Yb,Tm的上转换发光特性

利用水热法合成了掺杂Tm3 和Yb3 的YLiF4材料, 并研究了Tm3 和Yb3 在材料中的光吸收, 以及980 nm红外光激发下不同Tm3 浓度掺杂下的上转换发光特性. 实验发现, 在980 nm激光激发下, 材料可发出可见光. 上转换发光光谱中包括蓝光和红光. 与蓝光相比, 红光强度要弱1～2个数量级. 上转换发光强度和浓度关系研究显示, 当Tm3 浓度为0.3% (摩尔分数)时上转换发光达到最强, 大于0.3% (摩尔分数)后发光开始减弱. 通过分析输出光强与泵浦功率的双对数曲线, 发现Tm3 的蓝光发射和红光发射均属于双光子过程.     

The nature of the C-defects in nickel and their rôle in the interpretation of radiation damage in metals

In previous Perturbed-Angular-Correlation (PAC) studies of the - emission of ¹¹¹In probe nuclei in cold-worked or particle-irradiated nickel, it has been found that thermal annealing in the temperature regime of recovery stage III leads to the formation of so-called C-defects (Cubic defects). This is indicated by the occurrence of a new frequency of about 80 Mrad/s, in addition to the frequency (200 Mrad/s) that is due to ¹¹¹In on substitutional sites. Obviously, the C-defects are complexes consisting of ¹¹¹In and the intrinsic point-defect species that migrates freely in recovery stage III. Therefore, they have played an important rôle in the long-standing controversy on whether the recovery-stage-III defects are vacancies (one-interstitial model) or self-interstitials (two-interstitial model). The present paper reports on a novel experimental effort to reveal the nature of the C-defects by combining PAC studies on nickel samples differently pretreated in a systematic way, investigations of the Extended X-ray Absorption Fine Structure (EXAFS) on In-doped nickel, and measurements of the decay rate of ¹¹¹In nuclei in the Electron-Capture-Induced Decay (ECID). On the basis of the results of these experiments it is concluded that the defects trapped by substitutional ¹¹¹In atoms (In_s) in recovery stage III are self-interstitials (I), as expected according to the two-interstitial model. Moreover, there is evidence that the C-defects are In interstitials on tetrahedral sites (In_i) that form exclusively in the vicinity of the specimen surface from In_s – I pairs via the reaction In_s+I In_i.     

Subsolidus phase relations and crystal structures of R-Ca-Cu-O (R=Nd, Sm, Gd, Tm) systems

The subsolidus phase relations of R₂O₃-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca_14−xR_xCu₂₄O₄₁ (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca_2+xR_2−xCu₅O₁₀ (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca_14−xR_xCu₂₄O₄₁ possesses a layered orthorhombic structure and is isostructural to Sr_14−xCa_xCu₂₄O₄₁. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca_2+xR_2−xCu₅O₁₀ solid solution is isostructural to Ca_2+xY_2−xCu₅O₁₀, the structure of which is based on an orthorhombic “NaCuO₂-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.     

大尺寸掺钕和掺铥铝酸钇晶体的生长和退火技术

通过分析铝酸钇(YAP)晶体产生孪晶、开裂、色心和弥散性散射的原因,探讨了克服这些缺陷和问题的技术途径.采用提拉法生长了b轴方向的掺钕和掺铥铝酸钇(Nd:YAP和Tm:YAP)晶体,通过温场系统、生长工艺参数和切割工艺的优化,克服了晶体开裂的问题,晶体直径达到46mm;通过真空退火工艺,既显著减轻了紫外和可见区的色心吸收,又减小了晶体的应力,有助于克服晶体在加工过程中的开裂问题.晶体生长实验和晶体的显微观察表明:YAP晶体中的弥散状散射很可能同熔体中组分的均匀性有关,通过增大晶体的直径,增强强迫对流有助于减轻晶体中的弥散状散射.高质量b轴Nd:YAP和a轴Tm:YAP晶体已分别实现二极管泵浦大于140W的1.079μm和大于10W的1.99μm激光输出.     

飞秒激光辐照Tm:YAG晶体的紫外发光研究(英文)

本文报道了室温下飞秒激光辐照Tm∶YAG晶体的紫外光上转换荧光。Tm3+荧光的强度与泵浦光的功率之间的依赖关系揭示了晶体的上转换过程由三光子吸收过程所主导。研究表明上能级粒子的增加来自于Tm3+吸收一个泵浦光子跃迁到3H4能级后再吸收两个泵浦光子,然后离子跃迁至下能级产生上转换荧光。     

A narrow-linewidth continuous wave Ho：YAL03 laser with Fabry-Perot etalons

A narrow linewidth continuous wave Ho：YAP laser with two Fabry-Perot etalons pumped by a Tm：YLF laser is reported. The maximum output power reaches 8.3 W when the incident pump power is 15.8 W, with 52.5% optical-to- optical conversion efficiency and 62.6% slope efficiency. A stable laser output at 2118.1 nm is achieved, with a linewidth less than 0.4 nm （full width at half maximum）. The beam quality factor is M2- 1.25, measured by the traveling knife-edge method.     

掺铥PLZT透明光电陶瓷的光辐射特性

根据J-O理论研究掺Tm3+的光电陶瓷PLZT的激光潜能，利用Tm3+的420?2000 nm的吸收光谱拟合出了其强度参量，即?2=9.133￡10-21 cm2, ?4=1.529￡10-21 cm2和?6=1.712￡10-21 cm2，进而由强度参量计算了辐射跃迁几率、辐射寿命、荧光分支比和1865 nm荧光峰的受激发射截面等光学参数．