大尺寸高浓度掺杂Nd:GGG和Nd:YAG晶体的光谱性质

由于Nd3 离子半径0.112nm和Y3 离子半径0.101nm相差10.9%,使得Nd3 离子非常难于进入YAG晶体中。我们用温度梯度法生长了大尺寸高浓度(2.8 at%)的Nd:YAG晶体,同时与用提拉法Nd:GGG晶体进行了比较。分析了高浓度掺杂Nd:GGG和Nd:YAG晶体浓度猝灭问题。研究了不同浓度掺杂的猝灭效应。在同样的掺杂浓度下,我们发现它们的猝灭程度不同,其原因是两种晶体中ΔE(m is-)m和ΔE(m i s )m不同。     

激光晶体Nd3+:Gd3Ga5O12中的核心和小面生长

Nd3+:Gd3Ga5O12(Nd:GGG)晶体是热容固体激光器的一种重要的工作介质.采用提拉法沿〈111〉方向生长出了Nd:GGG单晶,利用激光器、应力仪和偏光显微镜等仪器和方法,对晶体的小面生长及核心等缺陷进行了观察,分析了小面生长的机理,并提出了消除这些缺陷的办法.通过研究,为改善生长工艺、生长大尺寸优质Nd:GGG晶体提供参考.     

Preparation and characterization of Nd doped gadolinium gallium garnet nanopowders and crystals

The structural and optical features of gallium gadolinium garnet (GGG) nanopowders doped with neodymium were investigated. Nanopowders of GGG:Nd were prepared by modified sol‐gel method using acetic acid as complexing agent. This way permitted to incorporate large amounts of dopant (up to 10 %) without destroying garnet structure. Small single crystals of Nd:GGG were grown by a μ‐pulling down method and spectroscopic features of nanopowders and their single crystal counterparts were compared. It has concluded that the Nd³⁺ ions are located preferentially in the same type of sites in crystal lattices of GGG:Nd nanopowders and their single crystal counterparts. In addition, it follows from the perfect agreement of emission wavelengths and line width recorded for nanopowders and single crystal samples that the crystal lattice of GGG in nanopowders is not distorted. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

5英寸Nd:GGG激光晶体的生长

本文介绍采用提拉法,运用上称重自等径技术(ADC)生长5inch的掺钕钆镓石榴石(Nd:GGG)晶体.通过调整生长工艺参数,优化温场结构,我们成功生长了5inch的Nd:GGG晶体.晶体外观完整,无宏观缺陷,有望作为激光工作物质用于强固体热容激光器中.此外,我们对晶体的外形和生长界面作了讨论.     

The radial selectivity of in-situ core-doped crystal rods grown by the double die EFG method

The radial selectivity of in-situ core-doped Cr, Nd: LiNbO₃ crystal rods, grown by the double die EFG (edge-defined film fed growth) method, has been investigated. Two crucibles are combined with an outer and inner die for ascending of different doped melts. The critical growth parameters affected by the diffusion depended spreading effect of the dopant within the melt meniscus have been estimated. The first experimental tests show a good agreement with the theoretical prediction. Single crystalline LiNbO₃ rods with a length of about 100 mm and an outer diameter of 5 mm consisting of sharp separated inner Cr- or Nd-doped core region with diameters between 1.5 and 4 mm were grown successfully.     

Distribution of oxidation states of Cr ions in Ca or Ca/Mg co-doped Cr:Y3Al5O12 single-crystal fibers with nitrogen or oxygen annealing environments

The valence states of Cr ions in Ca or Ca/Mg co-doped Cr:Y₃Al₅O₁₂ (YAG) single-crystal fibers are studied. The fibers were grown using the laser-heated pedestal growth method, followed by annealing treatments up to 1500 °C. The concentrations of the Cr³⁺ and Cr⁴⁺ ions in octahedral and tetrahedral sites in oxygen or nitrogen environments were characterized. Above 700 °C, migration of Cr⁴⁺ between octahedral and tetrahedral sites takes place; its relative stabilization energy was estimated. For Ca,Cr:YAG annealed in an oxygen or nitrogen environment, it was 0.25 and 0.3 eV, respectively. For Mg,Ca,Cr:YAG annealed in oxygen or nitrogen, it was 0.47 and 0.49 eV, respectively. For the Ca,Cr:YAG crystal fiber (Ca/Cr=113.1%) with oxygen annealing, about 35% and 2.5% of Ca ions took part in charge compensation for Cr⁴⁺ in the octahedral and tetrahedral sites, respectively. The density of oxygen vacancies depends on the concentration of Ca ions. The estimated ratios of the unreacted oxygen vacancies to total oxygen vacancies were about 63% and 88% for oxygen and nitrogen annealing, respectively. The main limitation on the concentration of Cr⁴⁺ in the tetrahedral site of YAG is the presence of unreacted oxygen vacancies.     

Nd^3＋：KGd（WO4）2激光晶体的研究

合成了一系列不同Nd     

Growth and properties of (Cr, Nd) doped GdCa4O(BO3)3 crystals

Optical quality Nd:GdCa₄O(BO₃)₃ (Nd:GdCOB) crystal and chromium sensitized crystal of Cr:Nd:GdCa₄O(BO₃)₃ (Cr:Nd:GdCOB) were grown by the Czochralski (CZ) method. The transmittance spectra was measured at room temperature on 7at%Nd:GdCOB and lat%Cr:7at%Nd:GdCOB samples. The absorption in the blue-UV region of Cr:Nd:GdCOB was larger than that of Nd:GdCOB, which matched the xenon flash lamp very well. A 3×3×10mm³ Nd:GdCOB sample without any antireflective coating was sidepumped using a pulsed dye-laser tuned to 595.4nm. The green-light output energy was 1.35mJ at a pump energy of 17.5mJ. The conversion efficiency was 7.7%, and the threshold energy was less than 1.2mJ which are the best results up to now to our knowledge. 3×3×7mm³ Nd:GdCOB and Cr:Nd:GdCOB samples without antireflective coatings were pumped using a flash pump source. The threshold for Cr:Nd:GdCOB was 0.9J while for Nd:GdCOB it was I.O.J. The output green light energy was 2.46mJ for Cr:Nd:GdCOB at a 10J flash pump energy and was 1.96mJ for Nd:GdCOB at the same pump energy, which clearly shows that Cr³⁺ ions have the sensitizing effect on the Nd³⁺ ions in Nd:GdCOB crystal.     

Modification of the crystal structure of gadolinium gallium garnet by helium ion irradiation

The structure of gadolinium gallium garnet (GGG) single crystals before and after implantation by He⁺ ions has been investigated using high-resolution X-ray diffraction methods and the generalized dynamic theory of X-ray scattering. The main types of growth defects in GGG single crystals and radiation-induced defects in the ion-implanted layer have been determined. It is established that the concentration of dislocation loops in the GGG surface layer modified by ion implantation increases and their radius decreases with an increase in the implantation dose.     

Cr,Nd:GSAG晶体生长、光谱及LD泵浦激光性能研究

Cr,Nd:GSAG是一种性能优良的激光晶体,但是关于它的LD泵浦激光性能的研究很少.用提拉法生长了Cr,Nd:GSAG晶体,测定了它的化学成分、结构,初步测试了它的激光性能.晶体的(111)面X射线摇摆曲线半高全宽为0.055°.采用Rietveld方法精修X射线粉末衍射谱得到了Cr,Nd:GSAG晶体的原子结构参数、温度因子等.Cr,Nd:GSAG的最强吸收峰位于808.6nm处,吸收截面为3.38×10-20cm2.808nm光激发下,Cr,Nd:GSAG的最强发射峰位于1060nm,发射截面为6.04×10-20cm2,并测得激光上能级4F3/2的荧光寿命为274μs.利用808nm连续波LD泵浦实现了1060nm的激光输出,在输入功率为8.88W时,最大输出功率为0.513W,斜效率为6.73;,光-光转换效率为5.78;.此外还讨论了Cr,Nd:GSAG晶体中的Cr3+与Nd3+之间的能量传递机理.     

On normal kinetics in the case of some refractory and transition metals' crystallization

In given work the crystal growth kinetics connected with some refractory and transition metals is considered. For melts of Fe, Co, Ni, Cr, Zr, Ti, Ag, Cu, and Pb in the vicinity of melting temperatures the solid phase growth is described by means of a fluctuation theory applied for the macro-systems. By virtue of the “unlimited” and limited spectrum solid state particle concentration fluctuations' theory some effective kinetic coefficients have been estimated in the work. The effective kinetic coefficients are specific in the case of normal crystal growth kinetics. In the case of the crystallization of Fe, Co, Ni, Cr, Zr, Ti, Ag, Cu, and Pb-melts a comparison between two effective kinetic coefficients (based on the fluctuation theory and so-called equilibrium growth points density) has been realized. In most cases a satisfactory agreement between the effective kinetic coefficients has been observed.     

Recharging processes of Cr ions in Mg2SiO4 and Y3Al5O12 crystals under influence of annealing and γ ‐ irradiation

Recharging processes of chromium ions were investigated for Mg₂SiO₄:Mg, Cr single crystals using annealing in O₂ and in air and γ‐irradiation, as compare to YAG :Ca, Cr single crystals. The formation of tetravalent Cr ions in the Mg₂SiO₄ :Mg, Cr is related not only to the initial Cr content in the melt, oxygen partial pressure and O₂‐ vacancy existing in the crystal, but also to the external field such as γ‐irradiation. The additional absorption after γ‐irradiation shows the decrease in intensity of the absorption of Cr³⁺ and Cr⁴⁺ ions in some part of the spectrum and increase in the other giving evidence on recharging effects between Cr³⁺ and Cr⁴⁺. There arises also color centers observed between 380 nm and 570 nm that may participate in energy transfer of any excitation to Cr⁴⁺ giving rise to Cr⁴⁺ emission. Opposite to forsterite crystal, absorption spectrum of YAG:Ca, Cr crystal after γ‐irradiation reveals only increase in the absorption of the Cr bands. The observed behavior of the absorption spectrum of YAG:Ca, Cr crystal under influence of γ‐irradiation suggests that γ‐irradiation ionizes only Cr ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Thermal Conductivity of Monocrystalline Gallium Garnets Doped with Rare-Earth Elements and Chromium in the Range 6–300 K

The effect of the additions of rare-earth elements Nd, Sm, Eu and Tb on the thermal conductivity of gadolinium-gallium garnets and besides the influence of the joint doping with Nd and Cr on the thermal conductivity of gadolinium-gallium and more compound gadolinium-scandium-gallium, gadolinium-magnesium-zirconium-gallium and yttrium-scandium-gallium garnets have been investigated.     

O− centre formation in YAG crystals doped with rare earth ions

Colour changes of YAG crystals doped with rare earth ions and annealed in hydrogen, oxygen, vacuum or argon are described. The influence of UV irradiation is also given. Some crystals were further doped with Ca, Sr, Ba, or Cr, respectively. Yellow or brown colouring of the crystals is attributed to the O⁻ centre formation which causes an increase of the absorption peak at 395–410 nm. Most intensive colouring showed the crystals containing a combination of Yb or Eu with Nd or Cr after oxygen annealing followed by UV irradiation.     

Synthesis and Crystal Structure of NdCaGaO4

The crystal structure of the NdCaGaO₄ compound was investigated by means of X-ray structure analysis (powder diffractometer HZG-4, CuK_α): structure type LaCuO₄, space group Cmca, a = 5.3700(2) Å, b = 12.1058(3) Å, c = 5.3937(2) Å, Z = 4, R_I = 0.126. The shortest interatomic distances are: Nd(Ca)—O — 2.240(14) Å; Ga—O — 1.913(2) Å, O—O — 2.6852(2) Å, Nd(Ca)—Nd(Ca) — 3.442(3) Å, Nd(Ca)—Ga — 3.154(4) Å, Ga—Ga — 3.8056(2) Å. Atoms have the following coordination numbers: Nd(Ca) — 8; Ga — 6; O1 — 14(6); O2 — 9(5).     

Mg掺杂对CaMnO3基热电氧化物电子结构及电性能的影响研究

采用超软赝势密度泛函理论计算的方法研究了Mg掺杂Ca位CaMnO3基复合氧化物的能带结构、电子态密度和电荷分布状况,在此基础上分析了Mg掺杂氧化物的电性能.结果表明,Mg掺杂CaMnO3氧化物仍然呈间接带隙型能带结构,带隙宽度由0.756eV减小到0.734eV.CaMnO3氧化物和Mg掺杂CaMnO3氧化物的自旋态密度曲线极值点均位于为-0.8eV附近.Mg掺杂CaMnO3氧化物中Mn原子对体系费米面态密度的贡献有所减小,O原子和Ca原子对体系费米面态密度的贡献有所增大.Mg原子比Ca原子具有更强的释放电子的能力,Mg掺杂对于CaMnO3氧化物属于电子型掺杂.Mg掺杂CaMnO3氧化物导电性能增强,电性能提高.     

Crystal growth and optical characterization of Cr,Ca: Y3Al5O12

Single crystals of Cr,Ca: Y₃Al₅O₁₂(YAG) with different Cr and Ca concentrations were grown by the Czochralski (CZ) and floating zone (FZ) method. The analysis of absorption and emission spectra of both as-grown and oxygen-annealed crystals in relation to concentration ratio of Ca and Cr (Ca/Cr) showed that Cr⁴⁺ concentration ratio to total Cr concentration increased up to about Ca/Cr = 6, and Cr⁶⁺ can also exist. Luminescence lifetime at 1400 nm was measured as a function of Cr⁴⁺ concentration.     

Melting enthalpy ΔHm for describing glass forming ability of bulk metallic glasses

A new melting enthalpy ΔH_m criterion for the prediction of glass forming ability (GFA) of alloys is proposed and five Zr–Al–Ni–Cu bulk metallic glasses (BMG) with critical dimension Z_max up to ? 7.5 mm are also developed by us in the light of the optimum ΔH_m of Zr–Al–Ni–Cu alloy system. And then, we researched the relationships between ΔH_m and two GFA parameters (critical cooling rate R_c and Z_max) of five bulk metallic glass (BMG) systems, such as Mg–Ni–Nd, Pd–Cu–Si, La–Al–Ni–Cu, Zr–Al–Ni–Cu and Zr–Ti–Ni–Cu–Be, respectively. The results show that the relationships between ΔH_m and R_c are all concave upward parabolas, and the optimum ΔH_ms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.3960 kJ mol^?1, 21.2202 kJ mol^?1, 19.7146 kJ mol^?1, 18.1455 kJ mol^?1 and 13.1558 kJ mol^?1, respectively. On the contrary, the relationships between ΔH_m and Z_max are all concave downward parabolas, and the optimum ΔH_ms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.5530 kJ mol^?1, 21.0830 kJ mol^?1, 19.6603 kJ mol^?1, 19.7231 kJ mol^?1 and 13.1173 kJ mol^?1, respectively. Furthermore, other BMGs’ R_cs or Z_maxs predicted by above-mentioned relationships satisfactorily agree with the tested results, which indicates that these relationships are reliable. However, the predicted results are reliable only if the main components are similar with the fitted BMGs or the additive is sparkle enough that the alloy’s character does not change. On the whole, the ΔH_m can act as a criterion for quickly predicting the alloy’s GFA and be helpful for the development of new BMGs.     

Growth and Optical Properties of Doped LiTaO3 Single Crystals

Single crystals of lithium tantalate (LiTaO₃) doped with Pr, Nd + Yb and Tm were grown by the Czochralski method. A thermal system with 50 mm diameter iridium crucible and two different afterheaters (active and passive) was checked with respect to temperature distribution in a pulling region. The obtained crystals were up to 20 mm in diameter and up 50 mm in length. Crystals were poled, and the Curie temperature was determined for specimens cut of from different parts of single crystals. The polarized absorption spectra, time resolved emission spectra and emission lifetime of Pr³⁺ doped LiTaO₃ crystals were measured. An intense emission from the ³P₀ level was observed. Optical properties of the Yb³⁺ ions excited by energy transfer from Nd3+ ions have been researched for LiTaO₃:Nd, Yb crystals.     

The short-range order in ternary ZrF4---BaF2---ErF3 glasses

The short-range order structures in ternary ZrF₄---BaF₂---ErF₃ glasses have been studied by X-ray absorption fine structure (XAFS). The near-neighbor structures around Zr, Ba and Er have been determined and compared with that in binary ZrF₄---BaF₂ glasses. The near-neighbor structures around Zr and Ba are scarcely affected by doping with ErF₃. The structural parameters of near neighbors around Er in the glasses are near to that in ErF₃, but the corresponding distance and coordination number of near neighbors in the glasses decrease slightly. It is also observed that the intensities of the white lines at the Er L and L absorption edges in these glasses are different from that in c-ErF₃. Meanwhile, compared with that of the corresponding fluoride, the changes of the ‘white line’ at the Er L_,-edges in the glasses differ from the case of Nd. The causes leading to these differences are discussed.