Characteristics and optical spectra of V : YAG crystal grown in reducing atmosphere

A V:YAG single crystal was grown by the temperature gradient technique (TGT) with graphite-heating elements. The as-grown crystal has different colorations of light green and yellow brown in different parts. Distribution of vanadium in three samples with different colorations was determined by inductively coupled plasma-mass spectrometry. From the absorption spectrum of the yellow-brown part with peaks at 370, 820 and 1320nm, we can deduce that the reducing atmosphere of carbon diffused from the heating elements can increase the concentration of tetrahedral V3+ ions and induce F color centers. All three samples exhibited light-green color after annealing in vacuum or H-2 atmospheres. In the vacuum annealing process, the V3+ ions in tetrahedral positions were enhanced through two methods: one method is the exchanging of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under thermal excitation, the other is that F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states to further improve the concentration of tetrahedral V3+ ions. Besides the two mechanisms, the H-2 annealing process greatly improved the V-tetra(3+) ions through the reduction effect of H-2. (c) 2006 Elsevier B.V. All rights reserved.

大尺寸高浓度掺杂Nd：GGG和Nd：YAG晶体的光谱性质(英文)

由于Nd^3＋离子半径0．112nm和Y^3＋离子半径0．101nm相差10．9％，使得Nd^3＋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△Emism（-）和（＋） △Emism（＋） 不同。

A comparison between TGT and Cz grown Nd : YAG

Large sized neodymium-doped Y3Al5O12 (Nd:YAG) laser crystals have been grown by temperature gradient technique (TGT) method and compared with Czochralski (Cz) method. The comparison of these two crystal growth methods has been listed. The results showed that the TGT method has many advantages over the Cz method. The concentration distribution of Nd ions in the crystals was determined and the absorption spectra of these crystals have been investigated and compared. The TGT grown highly doped Nd:YAG crystal has a larger absorption FWHM than that of Cz grown Nd:YAG crysral. Highly doped Nd:YAG (similar to 2.8 at. pct) crystals could be obtained by TGT.

Color centers and charge state change in Ce : YAG crystals grown by temperature gradient techniques

Color centers and impurity defects of Ce:YAG crystals grown in reduction atmosphere by temperature gradient techniques have been investigated by means of gamma irradiation and thermal treatments. Four absorption bands associated with color centers or impurity defects at 235, 255, 294 and 370 nm were observed in as-grown crystals. Changes in optical intensity of the 235 and 370 nm bands after gamma irradiation indicate that they are associated with F+-type color center. Charge state change processes of Fe3+ impurity and Ce3+ ions take place in the irradiation process. The variations of Ce3+ ions concentration clearly indicate that Ce4+ ions exist in Ce:YAG crystals and gamma irradiations could increase the concentration of Ce3+ ions. Annealing treatments and the changes in optical density suggest that a heterovalent impurity ion associated with the 294 nm band seems to be present in the crystals. (c) 2005 Elsevier B.V. All rights reserved.

Color centers in Yb : YAG crystals grown by temperature-gradient techniques

Yb: YAG (Yb: Y3Al5O12) crystals have been grown by temperature-gradient techniques (TGT) and their color centers and impurity defects were investigated by means of gamma irradiations and thermal treatment. Two color centers located at 255 and 290 nm were observed in the as-grown TGT-Yb: YAG. Analysis shows that the 255 nm band may be associated with Fe3+ ions. Absorption intensity changes of the 290 nm band after gamma irradiation and thermal treatment indicate that this band may be associated with oxygen-vacancy defects. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

温度梯度法生长Nd：YAG晶体的1200W激光输出

用温度梯度法（TGT）生长了大尺寸的Nd：YAG激光晶体，测试了室温下的吸收谱并利用吸收谱研究了Nd离子在YAG晶体中的分布。比较了温度梯度法与提拉法生长晶体的区别。根据热容激光的原理，利用生长的Nd：YAG激光晶体片设计了热容激光器，利用侧面抽运，获得了1200w的激光输出，工作时间为2s，光-光转换效率为30％。

国产Nd：YAG陶瓷获得激光输出

近年来Nd：YAG多晶陶瓷作为激光介质得到了越来越多的重视，我国在这个方向也开展了大量的研究工作，Nd：YAG多晶陶瓷与Nd：YAG单晶相比有很多优点：容易制造、成本低、可以制造大尺寸和高掺杂浓度的材料，且无浓度梯度，机械特性良好，硬度比单晶大1．5倍，断裂韧度比单晶大5倍，并且可制备多层和多功能的陶瓷结构、可大批量生产，已经获得了比Nd：YAG单晶更高的效率，因此钇铝石榴石透明陶瓷是理想的钇铝石榴石单晶激光介质材料替代品。但国产陶瓷由于质量不佳，透明度不是很高，一直未能获得激光输出。

Cr,Yb:YAG晶体的自调Q激光性能

用光纤耦合激光二极管抽运Cr,Yb:YAG晶体获得了1.03 μm的自调Q激光输出,输出的调Q脉冲非常稳定,抽运阈值功率为680 mW,脉冲宽度为3.3 ns,获得的平均功率为156 mW,斜率效率为18.5%。随着抽运功率的增大,重复频率成线性增长,而脉宽略有减少,单脉冲能量和峰值功率都始终呈增大趋势。光束质量因子M2为1.17。

提拉法Tm：YAG晶体的生长缺陷研究

采用提拉法(CZ)生长了质量优异的Tm：YAG晶体．部分晶片在1000℃的空气气氛中退火25h．借助光学显微镜、扫描电子显微镜(SEM)，结合化学腐蚀法，对Tm：YAG晶体退火前后(111)面的缺陷特征进行了研究．Tm：YAG晶体(111)面的位错腐蚀坑呈三角形．在偏光显微镜下观察了退火前后Tm：YAG晶体(111)面的应力双折射．同时应用高分辨X射线衍射法测定了晶体的完整性．实验结果表明，长时间空气气氛下高温退火有效降低了晶体中总的位错密度，提高了晶体质量．

Yb：YAG晶体的闪烁特性

通过不同Yb^3＋掺杂浓度（5％-30％，原子数分数）的Yb：YAG晶体的阴极射线发光谱、衰减时间、光输出及其温度依赖关系的测量，研究了Yb：YAG晶体的闪烁性能。不同Yh^3＋掺杂浓度的Yb：YAG晶体具有不同的光输出和猝灭温度，光输出随Yb^3＋掺杂浓度的增大而降低，猝灭温度则随掺杂浓度的增大而升高。室温下Yb：YAG晶体的发光衰减时间较短，均小于50ns。Yb^3＋掺杂浓度为5％的Yb：YAG晶体具有较高的光输出和较低的猝灭温度。

Nd：YAG透明陶瓷的烧成及其显微结构

由溶胶一凝胶／燃烧合成结合法合成了Nd：YAG(掺钕钇铝石榴石，neodymium—doped yttrium aluminium garnet)粉体，用真空烧结法制备了Nd：YAG透明陶瓷。研究了显微结构随烧结温度和保温时间的变化，并对透明陶瓷的晶界结构和成分分布进行了表征。随着烧结温度的提高和保温时间的延长，Nd：YAG陶瓷的密度增大，晶形发育完整，透过率提高。晶粒内部和晶界的化学组成基本相同。所制备的Nd：YAG透明陶瓷在激光工作波长1064nm的透过率达到75％。

Yb：YAG及Cr，Yb：YAG晶体的发光特性

研究了室温下Yb：YAG的上转换荧光光谱，此荧光归因于Yb^3＋离子的“合作”发光和Yb抖离子到稀土杂质离子的能量转移。测试了Yb；YAG晶体的X射线荧光，发光峰对应于电荷迁移态到Yb^3＋离子的基态、激光态间的跃迁。研究了Cr，Yb：YAG晶体的荧光光谱。讨论了Cr^4＋激光输出的可能性。

Tm：YAG晶体的研究进展

Tm：YAG晶体是性能优异的LD泵浦激光晶体。本文总结了Tm：YAG晶体的生长、光谱性质以及激光性能的研究和发展，并指出了Tm：YAG晶体发展中需要解决的问题。

Optimization of thermal environment during crystal growth of large-sized Nd : YAG by Temperature Gradient Technique

A finite-element model is employed to analysis the thermal environments in Temperature Gradient Technique (TGT) furnace during the growth of large-sized Nd:YAG crystal. The obtained results show that when the crucible is located at the lower position inside of the heater, a flatter solid-liquid interface is established, which makes it easier to obtain the core-free Nd:YAG crystal. Meanwhile, the lower crucible position can induce higher axial temperature gradient, which is beneficial to the release of latent heat. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spectral properties of Ho : GdVO4 single crystal

Absorption and emission spectral properties of GdVO4 single crystal doped with Ho3+ ions were investigated at room temperature. Polarized absorption cross section is calculated in the range of 400-2200nm. Results were analyzed and parameters were calculated based on Judd-Ofelt theory, the emission spectrum shows that the emission intensity around the wavelength of 546 nm associated with transition S-5(2) -> I-5(8) is much stronger than other bands in the observed range and potentially enable the green light output around this emission band in this crystal. (c) 2006 Elsevier B.V. All rights reserved.