【作者】 周时凤；

【导师】 邱建荣； 郝建华；

【作者基本信息】 浙江大学 ， 材料学， 2008， 博士

【摘要】 随着计算机网络和通讯技术的发展，超大容量信息传输和超快实时信息处理已经成为光纤通讯的两个重要研究内容。目前，光纤制备技术的改进已经使光纤通讯的窗口覆盖了1-2到1．7μm的整个近红外波段。传统的稀土离子掺杂光纤放大器由于稀土离子发光峰窄的本征特点，表现出两个突出问题是：（1）有些波段处未有合适的稀土光纤放大器；（2）利用一根光纤一个泵浦源不能实现整个光通讯波段的光放大。如果能够设计和制备新型的红外增益材料，通过该材料制备的一根光纤就可实现多个波段甚至是整个光通讯波段的光放大，势必会给光通讯技术的发展带来很大的推动作用。本文系统介绍了稀土离子，过渡金属离子，主族元素离子掺杂材料和半导体量子点作为红外增益材料的研究进展，概括和评述了宽带近红外增益材料发展还面临的问题，并就其今后的发展进行了展望。在此基础上，我们围绕新型增益材料研究几个重要内容，即“可调谐”、“超宽带”、“多功能”、“高效率”和“微纳”，介绍了我们进行材料设计和构造的研究思路，诸如“配位场调控”、“利用微孔环境稳定多重发光中心”和“超短脉冲空间选择性诱导发光中心的转变”，并开发出几类新型近红外宽带发光材料。利用热分析，X射线衍射，高分辨透射电镜，拉曼散射光谱，电子自旋共振，透过/吸收光谱和光致发光光谱等表征手段研究了Ni和Bi离子激活材料的微观结构和光谱性能。本研究取得了一系列实验结果为新型宽带近红外增益材料的开发和实用化奠定了基础。研究了Ni²⁺离子掺杂ZnO-Al₂O₃-SiO₂微晶玻璃近红外宽带发光的机理，结果发现宽带红外发光源于掺入ZnAl₂O₄微晶Ni²⁺离子的³T₂（F）→³A₂（F）跃迁，而并非是玻璃相中的Ni²⁺璃子。在此基础上提出了该类材料的设计原则：Ni²⁺离子必须掺杂入微晶的八面体格位。并进一步设计和制备了两种新型Ni²⁺离子激活红外宽带发光材料：Ni²⁺离子掺杂MgO-Al₂O₃-SiO₂和Li₂O-Al₂O₃-SiO₂微晶玻璃材料。对不同热处理工艺条件下获得的Ni²⁺掺杂Li₂O-Al₂O₃-SiO₂微晶玻璃的发光性能进行了研究，结果发现在保证微晶玻璃透明的温度范围内（600-800℃）随着热处理温度的升高发光减弱，随着热处理时间的延长发光增强且发光峰蓝移。探讨了上述现象的起因：Ni²⁺离子发光对环境很敏感，不同热处理工艺不仅影响微晶结构，也影响Ni²⁺离子所占据格位的分布。提出两个可实现可调谐发光的研究思路：（1）利用微晶玻璃中纳米微晶的小尺寸效应调控光学性能；（2）利用配位场调控实现可调谐发光。设计并成功制备了具有可调谐红外宽带发光特征的Ni²⁺离子掺杂微晶玻璃材料。利用纳米材料特殊的微观结构特点，在Ni²⁺离子掺杂γ-Ga₂O₃微晶玻璃中，通过调控热处理温度控制析出纳米微晶的尺寸（4．8-11．7 nm），实现了40 nm（1240-1280 nm）的近红外宽带可调谐发光。分析可调谐发光的起因：微晶玻璃中不同尺寸的纳米晶表现出不同程度的结构畸变，引起过渡金属离子和周围配体的相互作用程度不同，从而影响中心活性离子的能级分裂。进一步通过直接控制中心活性离子和配位体的相互作用，在γ-Ga₂O₃，Mg₂SiO₄和Ba_0.808(Al_1.71Si_2.29)O₈透明微晶玻璃中，首次实现了覆盖整个近红外波段，发光峰可从1245 nm调至1450 nm和1570 nm的宽带可调谐发光。理论分析确认可调谐发光是通过调控微晶中活性离子与氧离子的键长实现。该方法具有普适性，可用于设计工作在其它波段的新型发光材料，有望解决传统半导体量子点可调谐发光材料的环境性问题，并在生物和通讯领域获得应用。提出利用单一离子掺杂实现超宽带发光的研究思路：利用活性离子掺杂进入同一微晶中两个不同的晶格位置，通过发光峰的组合实现超宽带发光的目的。基于上述设计思想成功制备了具有超宽带红外发光特征的新型Ni²⁺离子掺杂（Ga₂O₃）₃（GeO₂）₂微晶玻璃材料并对其结构和光学性能进行研究。EELS和光谱分析结果表明Ni²⁺离子分别掺杂进入了规则和变形GaO₆八面体。处于规则八面体的Ni²⁺离子具有较强的晶体场能量，发光中心波长处于高能量区域（1300 nm）；而处于变形八面体位置的Ni²⁺离子具有较弱的晶体场能量，发光中心波长处于低能量区域（1450 nm）。通过两个发光峰的组合实现半高宽达400 nm的超宽带近红外发光。激发光谱和瞬态光谱的表征结果表明不同格位的发光中心存在传能过程，且该传能效应可被利用作仅通过选择不同激发波长来实现红外发光的可调控。最后提出了过渡金属离子掺杂的机理：基于系统能量最小的稳定化趋势是过渡金属离子格位选择的驱动力。上述结果为利用通过掺杂改变纳米材料发光性能的研究提供重要参考。基于前面Ni²⁺离子近红外波段宽带发光机理的探讨，选取宽禁带宽度和低声子能量的β-Ga₂O₃作为Ni²⁺离子的基质，并成功制备了Ni²⁺离子掺杂β-Ga₂O₃透明微晶玻璃材料。光普性能表征结果表明与报道的Ni²⁺离子掺杂ZnAl₂O₄和LiGa₅O₈微晶玻璃体系相比，Ni²⁺离子掺杂β-Ga₂O₃微晶玻璃材料在近红外波段具有更强的发光和更长的荧光寿命。利用单组态坐标模型（Single Configurational Coordinate）探讨了上述现象的起因，分析表明和Ni²⁺离子在该体系中具有较强晶体场能量及β-Ga₂O₃基质具有相对较低的声子能量有关。以980 nm激光作为泵浦源，在Ni²⁺离子掺杂β-Ga₂O₃透明微晶玻璃中首次演示了宽带光放大现象，于光通讯第二窗口处获得了77 nm宽带增益，估算了1300 nm处的增益系数为0．283 cm^-1。上述结果表明新型Ni²⁺离子掺杂β-Ga₂O₃微晶玻璃有望用于宽带光纤放大器。利用主族元素离子（Bi）特殊的电子构型特点，提出通过玻璃网络形成体组合，调控红外发光性能的研究思想。成功设计和制备了具有超宽带，可调谐发光和平坦增益的Bi离子激活材料，并对其结构和光学性能进行研究。通过二氧化锗和二氧化硅的组合，在Bi掺杂锗硅酸盐玻璃体系中首次报道了同时覆盖1272-1348 nm和1560nm的超宽带光放大，性能较Bi掺杂锗酸盐玻璃体系优异。Raman光谱表征结果表明Bi离子掺杂锗硅酸盐玻璃体系发光峰的展宽和活性离子所处微结构环境的复杂性有关。文献报道利用在玻璃体系中添加网络改变体（BaO）并通过改变其含量调控近红外发光性能，但该方法的缺点在于随着网络改变体含量的增加红外发光性能有所降低。而本文中采用的玻璃网络形成体组合的方法可以很好的兼顾可调谐发光和高增益性能的要求。利用激发光谱研究了Bi离子掺杂锗酸盐玻璃红外发光特征对激发光源变化敏感的起因，结果表明和玻璃中存在分别具有低配场强度和高配位场强度的多个Bi发光中心有关。尝试给出了两个不同发光中心的能级构造，该结果为获得特定波段红外发光及平坦增益提供重要参考。进一步的光放大研究表明：采用特定波长的泵浦光（如980 nm）可以实现十分平坦的宽带增益。提出利用微孔作为特殊发光中心化学平衡调控和固定的微环境，设计和制备新型多功能发光材料的研究思想。设计并成功制备了覆盖可见到近红外波段的宽带多功能发光Bi掺杂材料，并对其光学性能进行研究。通过制备条件和激发波长的控制，在Bi掺杂多孔玻璃中实现了蓝绿光，白光，紫红光和橙光的可调谐发光，该可调发光性能是通过调控Bi³⁺的465 nm和Bi²⁺的590 nm荧光峰的相对强度实现。在Bi掺杂多孔玻璃中同时也实现了分别位于1100 nm和1400 nm的近红外发光，且发光峰位可通过泵浦波长的选择进行调控。该研究的另外一个重要意义在于从实验上首次证明了Bi掺杂玻璃红外发光源于低价态的Bi离子，且很可能是Bi⁺中心。探讨了Bi离子红外发光在晶体基质中难实现的原因：Bi⁺离子具有较大的离子半径（与Rb⁺，Cs⁺离子相近），而多孔材料中的微孔则可以为大尺寸离子的稳定提供—个很好的环境。另外，在Bi离子掺杂多孔玻璃中通过氢气气氛的处理获得了含有Bi纳米晶的杂化材料，由于Bi金属具有在较低温度下热致相交的特殊性能，结合二氧化硅玻璃优良的耐热性，获得的杂化材料可作为热-光开光等应用。提出利用超短脉冲近红外激光在透明玻璃内部选择诱导多个特殊发光中心的变化，实现宽波段、多功能微纳光源的设计思想。基于多光子吸收原理，利用800 nm飞秒激光空间选择性调控Bi掺杂多孔玻璃的光学性能，成功实现了覆盖可见和整个近红外波段（800-1600 nm）的超宽带发光调控。发光的变化对应于Bi³⁺，Bi²⁺和Bi⁺多个发光中心的转变。超短脉冲激光选择性照射Bi掺杂硅酸盐玻璃的研究发现外场调控不仅可以实现可见波段的光色效应，还可以有效擦除近红外特定波段处的荧光峰。该实验现象和非线性效应产生的自由电子和空穴与多个发光Bi离子的作用有关：Bi²⁺离子和自由电子和空穴复合引起可见波段光吸收特征的变化；处于玻璃网络结构中不稳定的Bi⁺离子与自由电子和空穴复合引起近红外波段一发光峰的擦除。上述研究利用近红外飞秒激光在Bi掺杂玻璃中实现从可见到近红外波段超宽带范围的发光调控，可见波段区域的光色效应及红外波段特定发光峰的擦除，在微纳光子学领域有重要应用，如可进行各种三维微纳有源元器件的构造和加工；利用发光和吸收的变化也可实现超高密度三维光存储。更多还原

【Abstract】 With the speedy development of computer network and telecommunication technology, optical fiber transmission technology with high speed and high capacity is demanded. Recently, great progress has been achieved in the OH elimination of silica fibers, and as a result, the telecommunication transmission has been extended to the range from 1.2 to 1.7μm. Therefore, considerable effort has been devoted to the development of optical fiber amplifiers which can be used to produce optical gains at different communication bands. For examples, erbium （Er）-doped fiber amplifiers provide gain in the C band （1530-1565 nm）, L band （1570-1605 nm） and S band （1450-1520 nm）. Some other types of the amplifiers such as thulium （Tm）-doped amplifier in the S band （1450-1520 nm） and praseodymium （Pr）-doped amplifier in the O band （1260-1360 nm） were also developed. If we want to realize optical amplification in the whole telecommunication window by using rare-earth-ions-doped amplifiers, the only way is to combine different types of existing amplifiers. So the broadband amplification in the whole 1300-1600 nm region by using only a fiber would be expected to simplify the configuration of optical amplifiers and revolutionize the present telecommunication systems.This thesis provides a comprehensive review on the luminescence characteristics of rare-earth, transition-metal and main-group ions doped materials, gives an overview of the recent progress and problems, and puts forwards their future research directions. To develop the novel light source with the typical characteristics of "highly efficient", "wavelength tunable", "ultra-broadband", "multifunctional" and "micro-structured", several novel research ideas are presented, such as tuning optical properties of emission centers via tailoring the ligand-field, stabilizing multiple emission centers in a tolerant porous host and space-selective fabricating via ultra-short laser pulse. Based on these ideas, several new types of infrared luminescent materials have been developed successfully. Thermal analysis （DTA）, X-ray diffraction （XRD）, transmission electronic microscope （TEM）, Raman scattering spectroscopy, electron spin resonance （ESR）, absorption/transmission spectra, photoluminescence spectroscopy （PL） were used to study the structure and luminescence properties of the materials. A series of important conclusions and innovative results with practical significance were obtained.The infrared luminescence of Ni²⁺-doped ZnO-Al₂O₃-SiO₂ glass and glass-ceramics has been investigated. It is found that the infrared luminescence is originated from the ³T₂（F）→A₂（F） transition of octahedral Ni²⁺ ions doped into the nanocrystals. The result demonstrates that only octahedral Niv ions in crystalline hosts can act as infrared emission centers. On the above base, we designed two novel Ni²⁺-doped MgO-Al₂O₃-SiO₂ and Li₂O-Al₂O₃-SiO₂ glass-ceramics with broadband infrared luminescence and fabricated them successfully. The investigations on the optical properties of Li₂O-Al₂O₃-SiO₂ glass-ceramics treated at various conditions indicate that the luminescence characteristics of Ni²⁺ ions are very sensitive to the local environment The blue-shift of the peak position and the intensity decrease of the infrared luminescence could be attributed to the sites change ofNi²⁺ ions in the glass-ceramics.Two research ideas are proposed for designing the single ion doped materials which show tunable infrared luminescence: （1） tuning the infrared luminescence via controlling the size of the nanocrystals; （2） tuning optical properties of emission centers via tailoring the ligand field Transparent Ni²⁺-doped Li₂O-Ga₂O₃-SiO₂ glass-ceramics embeddedγ-Ga₂O₃ nanocrystals was prepared successfully and characterized. By controlling the size of the nanocrystals, the infrared luminescence is tunable. The result can be ascribed to the alteration of crystal field strength Dq of octahedral Ni²⁺, which is due the changes of the lattice parameters. Two novel M²⁺-doped glass-ceramics containing Mg₂SiO₄ and Ba_0.808(Al_1.71Si_2.29)O₈ nanocrystals were designed and fabricated successfully. The above-mentioned three types of glass-ceramics show interesting wavelength tunable luminescence from 1245,1450 to 1570 nm. The theoretical analysis suggests that the tunable luminescence is the result of fine controlling the internuclear distance between the active Ni²⁺ ion and the surrounding ligand. It is necessary to point out that the research idea can be potentially employed to design and fabricate novel soluble infrared luminescent nanocrystals with tunable characteristic as potential substitutes for the traditional Pb and Cd containing infrared-ernitting quantum dots with high toxicity.The research idea is proposed for designing the single ion doped materials which show ultra-broadband luminescence: controlling the luminescence from active Ni²⁺ ions occupied the multiple octahedral local environments. Transparent Ni²⁺-doped Na₂O-Ga₂O₃-GeO₂ glass-ceramics embedded （Ga₂O₃）₃（GeO₂）₂ nanocrystals were prepared successfully and characterized. According to EELS results, Ni²⁺ ions are incorporated into the multiple positions: one is in the regular octahedral position and the other is in the distorted one. Since the distortion of ligand may induce the weakening effect on the crystal field strength of central Ni²⁺ ion, the multiple centers may show different crystal field strength. Therefore, the material shows interesting luminescent characteristics with two emission bands at 1300 and 1450 nm originated from high crystal field Ni²⁺ ions and low crystal field ones, respectively. The mixing of these two bands presents ultrabroadband luminescence with the large full width at half maximum （FWHM） of about 400 nm. The corresponding photoluminescence excitation spectra and fluorescence decay curves suggest a possible energy transfer between above-mentioned two centers. As a result, infrared luminescence can also be tuned via changing pumping sources. Another interesting point observed in our experiment is related to the surprisingly effective doping. We suppose that the strong preference of active center for special coordination, octahedral position for Ni²⁺ here, might be the underling drive force for doping. The results may potentially provide useful reference for the present hot issue of doping in nanocrystals.Wide band gap semiconductorβ-Ga₂O₃ is selected as the host material for Ni²⁺ ion since the thermal-quenching effects are inversely proportional to the band gap of the hosts. Highly transparent glass-ceramics containingβ-Ga₂O₃:Ni²⁺ nanocrystals were synthesized successfully and characterized. Intense broadband luminescence centering at 1200 nm was observed when the sample was excited by a diode laser at 980 nm. The room-temperature fluorescent lifetime is 665μs, which is longer than the Ni²⁺-doped ZnAl₂O₄ and LiGa₅O₈ glass-ceramics and is also comparable to the Ni²⁺-doped LiGa₅O₈ single crystal. The intense infrared luminescence with long fluorescent lifetime may be ascribed to the high crystal field hold by Ni²⁺ ions according to the generalized single configurational coordinate diagram. In addition, the moderate lattice phonon energy ofβ-Ga₂O₃ may also favor the radiative transition of active Ni²⁺ ions. Furthermore, we demonstrated broadband optical amplification at 1.3 μm in glass-ceramics with 980 nm excitation for the first time. The optical gain efficiency is about 0.283 cm^-1 when the excitation power is 1.12 W. The optical gain shows similar wavelength dependence to luminescence spectrum. The obtained gain material has potential applications in broadband optical fiber amplifiers and tunable lasers.The research idea is proposed for designing Bi-doped materials which show ultra-broadband luminescence: tuning the composition of glass network former to favor the presence of multiple structural units around Bi centers. Bi activated germanium silicate glass was prepared successfully and characterized. The glass sample shows broadband and flat emission characteristics compared with germinate glass. Ultrabroadband optical amplification at 1272 and 1560 nm is observed simultaneously. It is possible that the presence of multiple structural units in the vitreous matrix in germanium silicate glass might provide more than one type of crystal field environment for Bi ions and as a result, inhomogeneous broadened emission and flatter spectrum are observed In comparison with the reported method such as adding glass modifiers （BaO and Li₂O） into the glass system, the presented way can give both considerations of tunable luminescence and high gain efficiency. Photoluminescence excitation spectra were employed to investigate the characteristic of excitation wavelength dependent luminescence in Bi doped germanium glass. Two active centers which occupy strong and weak crystal field environment are identified. The tunable and ultrabroadband luminescence properties are originated from electron transitions of these two active centers. The wavelength-dependent internal gains excited with 808 and 980 nm laser diodes show difFerent characteristics, and the relative flat optical amplification can be realized by choosing 980 nm pumping.A facile method is presented to realize multifunctional light source by stabilizing "active" centers （bismuth） in a "tolerant" host （nanoporous silica glass）. Highly transparent materials, in which, unusual multiple bismuth centers were stabilized, were prepared successfully and characterized. The novel hybrid system shows multicolor luminescence from blue-green, orange, red, and white to the near-infrared region and it can be potentially applied as a wide-spectrum light source. The luminescence mechanism is also discussed and the results provide evidence that infrared luminescence is originated from the low-valence-state Bi. We have also found that nanoporous matrices can potentially be used as templates for in situ preparation of Bi nanocrystals. This might be attractive because of its multiple physical effects, such as thermal-optical switching, light-induced reflectivity tuning, and enhancement of second-harmonic generation. It is believed that the Bi-doped nanoporous glass thus obtained shows optical performance superior to that in other matrices. We propose that immobilizing active centers in a nanocage structure provides a new platform for design and fabrication of novel transparent photonic materials.The research idea is proposed for space-selective fabricating of active multifunctional light source: employing ultra-short laser pulse to induce multi emission centers in a "tolerant" host We have demonstrated space-selective fabrication of ultra-broadband light source by femtosecond laser in the active "tolerant" host （Bi-doped nanoporous silica glass）. The acquired Bi²⁺ and multiple Bi⁺ centers show ultra-broadband luminescence covering from red to infrared region. Since the luminescence change are only limited in the focal spot, we believe the material can be fabricated into active micro or even nano-scale photonic components. In Bi-doped silicate glass, a novel photochromic phenomenon under irradiation of a femtosecond laser is reported. Not only broadband absorption in the visible but also infrared luminescence variations have been observed after irradiation. This behavior is related to the process of multiphoton absorption initiating local chemical reactions involving multiple active centers of Bi. The materials studied here pave the way to three-dimensional memory systems with ultra-high density, as well as micro-photonic components or devices operating in various spectral bands, including the technologically important low-loss telecommunication window.更多还原