氟化钙及掺质氟化钙晶体的生长、光谱与激光性能研究
文献类型：学位论文
| 作者 | 苏良碧 |
| 学位类别 | 博士 |
| 答辩日期 | 2005 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐军 |
| 关键词 | 氟化钙 晶体生长 光谱性能 激光晶体 二极管泵浦 |
| 其他题名 | Crystal growth, spectroscopic properties and laser performance of undoped and doped CaF2 crystals |
| 中文摘要 | CaF2晶体因其优异的光学和物化性能，以及独特的结构特征，在工业应用和科学研究两个领域一直都发挥着非常重要的作用。特别地，在（深）紫外光学元件和激光与光电子基质晶体两方面，CoF2晶体重新又散发出诱人的魅力。（l）CaF2晶体适合于用作真空紫外到红外波段的窗口材料，也是其它材料无法取代的复消色差透镜材料。（2）CoF2晶体是典型的萤石型结构，容许掺质离子高浓度的掺入，同时多样化的电荷补偿方式产生具有丰富对称性的格位结构。这种独特的结构特征赋予掺质CaF2晶体非常宽的吸收和发射光谱，非常有利于LD泵浦和实现可调谐、超短激光脉冲。以这两个方向为中心，本论文主要研究了纯CaF2、U：CaF2、Yb3＋（Na＋）：caF2、Er3＋，Yb3＋（ce3＋，Na＋）：CaF2晶体的生长，晶格缺陷，光谱特性，以及激光性能。总体上，本论文的研究工作包括四个方面的内容。第一部分，研究了纯CaFZ晶体的生长、缺陷与光学性质。采用TG-DTA分析CaF2粉末原料的热反应，合理地设计化料升温程序，实现了原料脱气去杂、氟化去氧等预处理过程与晶体生长的一体化。系统地研究了多个生长参数，如增祸材料、升温程序、温度梯度场、生长降温程序等，对晶体的杂质浓度，缺陷密度，结晶完整性和光学性质的影响。第二部分，研究了U：CaF2晶体中U离子的价态和光谱性能，以及色心结构模型与辐照效应。以UO2（NO3）2·6H2O为初始原料采用温梯法生长的U：CaF2晶体中u离子主要以＋3价态存在，u的分凝系数等于0.53.系统地研究不同颜色晶体的吸收光谱，结合晶胞参数分析，确珲了U6+离子的存在。通过空气退火实验，确定了一直存在争议的1．5um可饱和吸收带属于U4＋98OnmLd泵浦U3＋：CaF2晶体产生2．0-2．8um的宽带荧光发射，显示U3＋离子的4F5/2能级是4111八叶419八辐射跃迁的有效泵浦带。采用Roman光谱、热释光和Y辐照实验详细她研究了u：CaF，品体中晶格缺陷（色心）的类型、浓度、结构、激活能等参数。通过建立u，＋：caFZ晶体结构的高温热动力学演变模型成功地解释了u3＋的形成机理，同时推测出Us＋：caFZ晶体中含有（u艺一F几）和（u儿一F几一H）两种离子复合体。第三部分，研究了Yb3＋（YbZ＋）离子在caFZ晶体中的分凝特性，吸收和发射光谱，Yb3＋离子在1um波段的荧光寿命和量子效率，以及LD泵浦下的激光性能。第一次研究了Yb3＋离子在caFZ晶体中的电荷转移发光现象：163nm激发产生峰值分别位于330nln和570nln的两个发光带。首次系统地研究了Na＋作为电荷补偿离子在Yb3＋：caF2晶体中的掺杂效应，实验结果表明Na＋在多个方面扮演着非常重要的角色：调节Yb离子的分凝系数，使之在晶体中的分布更加均匀；显著地抑制处2＋离子的浓度；有效地阻止了Yb3＋离子团簇结构的形成，从而极大地提高了Yb3＋的上能级寿命和发光量子效率；可以在非常宽的范围内调制Yb3＋离子的吸收和发射光谱特性。根据Yb3+：CaF2和Yb3＋，Na＋：CaF2晶体的吸收和发射光谱，确定了Yb3＋离子上下能级的晶场分裂结构，并计算了它们的配分函数。根据光谱参数，通过理论计算分析了Na＋对Yb3＋激光性能的影响：随着Na＋离子掺杂浓度的增加，激光波长调谐范围先增加后减小，激光闭值功率密度单调显著下降。Yb3＋，Na＋：caFZ晶体在976nmLD泵浦作用下，闭值吸收功率仅70mw，对应着功率密度等于1．39kw／cm2，与通过光谱参数预测的数值非常吻合，两者相差仅5％。比文献报道的孔：caFZ晶体闭值功率密度6．37kw／cmZ降低了数倍。并且初步实现了从1036lnm到1059lun的调谐激光输出。第四部分，研究了Er3＋，Yb3＋双掺，Er3＋，Yb3＋，Na＋三掺，和Er3＋，Yb3＋，ce3＋，Na＋四掺CaF2晶体在980funLD泵浦下的上转换可见光和1．5林m发光特性，以及相关的能量转移机理。基于Na＋作为电荷补偿离子所起到的多重作用，它在Er3＋，Yb3＋共掺的CaF2体系中极大地提高了Yb3＋-r3＋的泵浦能量转移效率。当Er3＋和Yb3＋的掺杂浓度分别为2．oat％和5．oat％时，Na＋共掺引起上转换可见光发光积分强度增加36．7倍，同时1．5um发光积分强度也提高了2．3倍。首次提出了Er3十，Yb3＋，ce3＋，Na＋四元掺杂CaF2体系，研究表明CaF2晶体中ce3＋离子2F5几弓2F班和Er3＋离子4111几叶4113泛之间的能量差完全匹配，导致两者之间产生高效的共振能量转移。当E尸"的掺杂浓度等于0．2at％时，共掺2．oat％的ce3＋离子引起1．5um荧光强度增加了62倍。通过一个简化的速率方程模型，估算出Er3＋的、11几分4113口的分支比提高了40多倍。Er3＋和Yb3＋共掺体系中，能量上转换的主要机制是Yb3＋Er3+的能量转移，所以能量上转换过程的平衡状态不随Er3＋掺杂浓度的改变而发生明显变化。蓝光上能级2H9几的激发主要是以绿光上能级453／2为中间态，而以红光上能级4F9泛为中间态，吸收第三个光子上转换蓝光的过程不起主导作用。所有基于4113／2能级的上转换过程都不占主导地位。Er，Yb，ce，Na四元共掺caFZ晶体的1．5um发射光谱具有理想的光谱参数aexFWHM和。exem，两者均高于玻璃和其它晶体基质。不同粒子反转比例下，增益曲线的峰值波长基本保持在1．54um。特别是，增益截面曲线宽而平坦，有利于实现宽带调谐和超短脉冲激光运转。 |
| 英文摘要 | Calcium fluoride (CaF2) single crystal has been always playing important roles in industry applications and science studies, owing to its excellent optics, physics and chemistry properties, as well as unique structure. Particularly, CaF2 renewedly attracts a great deal of interest as deep ultraviolet optics and laser & opto-electronic hosts. On one hand, CaF2 has a large band gap as about 12eV, which makes it have high transmittance in deep ultraviolet region. CaF2 is also irreplaceable as lens materials for the compensation of chromatic aberration. On the other hand, as typical fluorite crystal, CaF2 allows impurities with high concentrations, and has various charge compensating methods giving rise to a rich multisite structure. Such a structure leads to broad absorption and emission spectra, comparable with those of glasses, which are favorable for the production of broadly tunable and femtosecond laser. Following the two directions, the dissertation was focused on the crystal growth, structure defects, spectroscopic properties, and laser performance of undoped CaF2, U:CaF2, Yb3+ (Na+):CaF2, Er3+, Yb3+ (Ce3+, Na+):CaF2 crystals, which was composed of four parts. In the first part, crystal growth, defects, and optical properties of CaF2 single crystals were studied. On the base of the TG-DTA analyses, the necessary heating procedure was designed in order to combine the purification processes with crystal growth in one system. The effects of growth parameters, including crucible materials, heating procedure, temperature gradient, and growth rate, on the impurities contents, density of dislocations, perfection of crystallinity, and optical properties were systematically studied. In the second part, valent states, spectra properties, structure of color centers, and the effect of heat-treating and irradiation were studied. Using UO2(NO3)2-6H2O as starting materials, U3+-doped CaF2 crystals were always produced by TGT, whose segregation coefficient was determined to be 0.53. U6+ ions were identified in U:CaF2 crystal grown in absence of PbF2 as an oxygen scavenger, through analyzing the absorption spectra in several samples with different colors, in combination with the unit cell parameters. The undefined broad absorption band at 1.5um was unambiguously ascribed to U4*, which was produced by heat annealing in air atmosphere at 800°C. The emission band of U3+ with FWHM of 23lnm covering 2.0 to 2.8um spectra domain was obtained under pumping by 980nm LD, indicating the level *Fsn of U3* is an effective pumping band. The defect parameters in U:CaF2, such as types, concentrations, structure, and activation energy, were detailedly determined through Raman spectra, thermoluminescence, and y-irradiation. The U4+->U3+ reduction mechanism was successfully explained by a high-temperature thermal kinetics evolution model of U4+:CaF2 lattice structure, which predicts the presence of two kinds of complexes, (U? - F~) and (U? - F~ -H). In the third part, the segregation characteristics, absorption and emission spectra of Yb ions, photoluminescence properties, quantum efficiency, LD-pumped laser performance of Yb3+ at lum spectra domain were presented. The charge-transfer emission at 330 and 570nm of Yb3+ in CaF2 was firstly produced under excitation at 163nm. For the first time, the effect of Na+ ions as charge compensators in Yb3+:CaF2 was systematically studied, which were discovered to play several important roles. First, adjust the segregation coefficient of Yb ions in CaF2 crystal. Second, greatly suppress the production of Yb2+ ions. Third, effectively prevent Yb3+ ions from clustering to improve quantum efficiency. Fourth, modulate the absorption and emission spectra properties of Yb3+ ions in CaF2 crystal in a large scope. According to the absorption and emission spectra, the crystal field splitting of the 2F7/2 and 2F5/2 levels of Yb3+ in Yb3+:CaF2 and Yb3+,Na+:CaF2 were determined, and then their partition functions were calculated. The effect of Na+ on laser performance of Yb + was estimated from spectra parameters. With increasing the dopant concentrations, the tunable laser wavelength range was estimated to increase in the first step, and then decrease, while the pump threshold power density monotonously decreases. Under LD pumping at 976nm, the Yb3+,Na+:CaF2 crystal exhibited a such low threshold pump power as 70mW. The corresponding power density is 1.39kW/cm2, just consistent with the value of 1.32kW/cm2 calculated from spectra parameters, which is much lower than that of Yb:CaF2 (6.37kW/cm2) reported in reference. The laser wavelength could be tuned from 1036 to 1059nm. In the fourth part, the photoluminescence characteristics of Er3+, Yb3+-doped CaF2 with or without Ce3+ or Na+ in the visible region through upconversion and 1.5um domain was studied under pumping at 980nm, and the involved energy transfer mechanisms were also analyzed. Owing to its multiple roles in Yb3+-doped CaF2 crystals, Na+ can greatly improve the energy transfer efficiency of Yb3+-+Er3+, resulting in the integral intensity of emission in visible region increasing by 36.7 times, and that of emission in 1.5um domain increasing by 2.3 times when the dopant concentrations of Er3* and Yb3+ were 2.0at% and 5.0at%, respectively. For the first time, the quaternary doping system of Er3+, Yb3+, Ce3+, Na+-doped CaF2 was studied. Experiment results indicated the resonant energy transfer efficiency between Ce3+(2F5/2-" 2F7/2)and Er3^4! 11/2-"^4113/2) is very high because of thoroughly-overlapped spectra. When the dopant concentration of Er3+ was 0.2at%, the codopant of Ce3+ enhanced the integral emission intensity in 1.5um domain by 62 times. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15542]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 苏良碧. 氟化钙及掺质氟化钙晶体的生长、光谱与激光性能研究[D]. 中国科学院上海光学精密机械研究所. 2005. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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