基于玻璃结构调控的稀土离子发光性质研究

【作者】 焦清；

【导师】 邱建备；

【作者基本信息】 昆明理工大学 ， 材料学， 2014， 博士

【摘要】 稀土离子掺杂的发光材料具有许多优异的性能,如光吸收能力强,色纯度高,色彩鲜艳,发射波长覆盖范围广,物理化学性能稳定等优点,因而在照明、显示、激光介质、光纤放大器、光通讯和储能等领域具有广泛的应用。但是作为发光离子,由于其独特的4f内层电子跃迁导致其发光效率相对较低。玻璃作为一种良好的发光基质材料具有许多优点：透明度高,成本较低,容易加工以及较高的发光效率等；而且,玻璃的近程有序,远程无序的结构优势可以直接进行高浓度的稀土离子等发光中心离子的掺杂,可以避免光圈效应,且具有工艺简单、产品质量稳定等优良性能,因而稀土离子掺杂的发光玻璃被广泛应用于光电领域,成为一类重要的发光材料。如何提高稀土离子在玻璃基质中的发光效率以及优化稀土掺杂玻璃的发光性能成为一个重要的研究内容,并对光电材料的基础研究和器件化发展具有重要的理论价值。实验证明稀土离子在无机玻璃中的结构状态是处于网络外的空隙中,主要以离子键的形式与阴离子(团)相连接,激活剂离子的发光性能以及光吸收能力很大程度上与网络形成体的这些阴离子团有关。此外,玻璃修饰体离子如碱(土)金属离子等对激活剂离子的发光性质也会产生一定的影响作用。因此,通过对玻璃基质结构的调控可以实现对稀土离子的发光性质的调节,具体研究内容如下。本文制备了一系列稀土离子掺杂硼酸盐玻璃,并通过硼酸盐玻璃结构的变化,讨论了结构对稀土离子发光性质的影响机制。硼酸盐玻璃不仅是一种低熔点易制备的玻璃体系,而且具有特殊的结构单元。当在纯的B203玻璃中加入适量的碱金属或者碱土金属离子时,网络结构中存在着[B03]单元与[B04]单元的转变,进而对稀土离子的发光产生重要影响。在本文中,通过玻璃网络形成体B203和网络中间体A1203的变化,对稀土Eu3+离子掺杂的B2O3-Al2O3-Na2O硼酸盐玻璃体系的发光性质进行了研究。结果表明：随着网络形成体B203和网络中间体Al2O3含量的增加,在空气气氛下实现了Eu3+的自还原现象；而且随着玻璃组分浓度的增加,Eu2+的发光强度显著增强,并在较高A13+浓度样品中实现了自还原效率的显著提高。玻璃结构测试表明随着B2O3/Al2O3浓度的提高,玻璃的结构发生了从[B04]向[B03]的结构转变,由[B04]为主的五硼环、三硼环和四硼环等高聚态结构转变为[BO3]为主的原硼环,硼氧环以及焦硼环等低聚态结构。并且在结构转变的过程中,伴随有大量的负电荷产生,与网络间隙中的Eu3+相结合,实现了Eu3+的还原作用。因而,通过玻璃本身结构的调控可以实现对稀土离子发光性质的调控。由于等离子体共振的作用,玻璃中的金属纳米颗粒也可以对稀土离子的发光产生影响,但技术纳米颗粒在玻璃中的形成机制、金属离子的赋存状态以及它们对稀土离子发光的影响规律尚不明确,因此,本论文通过改变硼酸盐玻璃结构研究金属离子在网络中的赋存状态产生,并通过研究金属离子或纳米颗粒与稀土离子之间能量传递的关系,以期实现对稀土离子发光的调制。我们发现随着玻璃结构中[B04]单元向[B03]单元的转变,贵金属Ag的赋存状态发生了高聚态向低聚态的结构转变,即Ag+和Ag团簇的发光呈现增强的趋势,而Ag纳米颗粒的析出能力下降,金属离子的这种赋存状态变化对稀土离子的发光性质具有良好的促进作用。低聚态的Ag粒子通过能量传递作用促进了Eu3+的发光效率,这表明通过玻璃的结构调控可以实现金属离子的赋存状态调节,进而实现对稀土离子发光性质的优化调控。同时,在Eu-Ag共掺的样品中,实现了光谱从红光到蓝紫光的较大范围内的光谱颜色调控,并最终分别在Eu单掺的样品和Eu-Ag共掺的样品中实现了玻璃的白光发射,我们对Ag赋存状态与硼酸盐结构的关系以及Eu-Ag共掺玻璃中的能量传递机理做了推测分析。由上可知,通过改变玻璃自身的组分,可以对玻璃的内部微观结构进行选择性调控,进而实现对稀土离子发光行为的调制。在本文中,我们提出采用外场作用方式,即通过飞秒激光辐照对玻璃结构的诱导作用进行了相关研究,进而研究了激光诱导结构与稀土离子发光性质的相互关系。我们发现,飞秒激光作用到Sm3+掺杂的氟铝酸盐玻璃体系时,在激光焦点处由于多光子电离等的产生诱导了玻璃中的微纳结构,进而实现了部分Sm3+的光还原。同时我们发现,飞秒激光作用于卤素离子Cl,Br取代部分F离子的氟铝酸盐玻璃后,Sm2+的发光明显出现增强,在高浓度Cl,Br取代的样品中呈现了非线性显著增强的现象。透射电镜测试结果表明,飞秒激光作用下的玻璃基质中析出了卤化物Cl,Br的的纳米分相,并且Sm3+选择性地进入到析出的卤化物纳米分相中,这可能是导致Sm3+的光还原能力显著增强的原因。另外,针对卤素Br替换的基质的Sm3+的光还原效率比C1离子替换的样品以及纯氟化物基质都要高的问题,我们提出了物质的电负性影响光还原的机制,即卤化物的电负性越低其所形成的微观环境的还原性越强,其光还原能力也越强。因此我们有理由相信,外场作用也可以实现对玻璃结构的调控,进而调控掺杂稀土离子的发光性质。更多还原

【Abstract】 Rare earth ions doped luminescent material exhibits many excellent properties, such as strong absorption ability, high color purity, and colorful hue, wild range of emission wavelength, stable physics and chemistry property. As a result, this kind of material has a wide range of application in many fields such as illumination, display, laser medium, fiber amplifier, optical communication, energy storage and so on. However, the emission efficiency is relative low because of their special4f electronic transition structure. Glass has many advantages as a host for luminescence materials:high transparency, low cost, easy processing and high luminescent efficiency etc. In addition, due to the special structure of glass-short-range order and and long-range disorder, high concentration of rare earth ions can be doped in glass. As a result, the halo effect can be avoided. Based on these, rare earth ions doped glass is an important material applied in photoelectric field widely. Therefore, it has important research significance in studying optical properties of rare earth ions doped glass, and how to improve luminescent efficiency of rare earth ions doped in glass has an important theoretical value in basic research and device project.Experiments demonstrated that rare earth ions are placed in the gaps outside the glass network in inorganic glass. They are connected with anion group mainly through ionic bonds. To a large extent, the luminescent properties of activators and their light absorption ability have relationships with networking formation anion group. Besides, the modifiers such as alkaline earth metal ions have a certain impact in the luminescent properties of activators. Therefore, the optical properties of rare earth ions can be regulated by the adjustment of glass structure. The main research contents are as follows:In this work, rare earth ions doped borate glasses are prepared. We discussed the influence of the glass structure on the rare earth luminescence by changing the borate glasses. Borate glass is famous for both low melting point and special structure units. The structure transition between [BO3] units and [BO4] units is existed in the glass when appropriate alkali metal ions or alkali-earth metal ions are doped in the B2O3glasses. This change will affect the emission of rare earth ions deeply. Herein, with variation of network forming B2O3and network medium Al2O3, the luminescent properties of Eu3+doped B2O3-Al2O3-Na2O glasses is investigated. The results indicate that with increasing of B2O3/Al2O3concentration, Eu3+ions are reduced to the divalent and the blue emission of Eu2+is observed in the air condition. Moreover, with increase of B2O3/Al2O3, the Eu+emission is enhanced evidently and the mutated growth of Eu2+luminescence happened in the higher Al3+ions doped samples. The structure detection revealed that the glass structure is turned from [BO4] units to the [BO3] units with increasing of B2O3/Al2O3concentration, which means the pentaborate groups, tetraborate groups consist of [BO3] and [BO4] units are turned to the low polymeric groups such as boroxol rings, triborate and orthoborate groups composed by the main [BO3] units. Moreover, during the decomposition process, low polymerized units with large negative charges are reacted with neighboring Eu3+ions leading to the Eu+ions reduction effect. It is therefore that the luminescence of rare earth ions can be controlled by the alternation of the glass structure induced by the varied composition.Owing to the good work of the plasma resonance, the metak nanoparticles in the glass matrix is available to influence on the luminescence of rare earth ions. However, the unclear problems are existed such as the formation mechanism of the technical nanoparticles in the host, the types of the metal ions and their rule effect on the rare earth ions emission. Therefore, The occurance state of the metal ions in the glass network is investigated by change of the structure of the borate glasses. And the avaible control on the rare earth ions luminescence is expected to be relized through the study of the energy transfer interaction between metal ions or nanoparticles and rare earth ions. It is found that the type of the noble silver is changed from their high polymeric state to the lower ones with transformation of [BO4] to [BO3] units. Namely, the luminesce intensity of Ag+and Ag aggregates is increased and the the precipitation ability of the Ag nanoparticles goes down. Fortunately, the variation is contributed for the emission of the doped rare earth ions. Energy transfer is proceeding from the low polymeric Ag species to the Eu3+ions emission efficiency. It is believed that the galss structure can be changed to control the type of the metal ions and then improve the luminescent properties of the rare earth ions in the glass.Accordingly, the variation of the glass component can selectively control the micro structure of the glasses and furthering to adjust the luminescence of the rare earth ions. In this paper, the external field mode is employed by the femtosecond laser irradiation into the glass to study their effect on the glass structure, including the interaction of the induced structure and the rare earth ions emission. The results indicates that part of doped Sm3+ions is reduced to the Sm2+in the laser focus where the micro structure is existed induced by the irradiation effect because of the multiphoton ionization. Not only that, but the luminescent efficiency is enhanced after the halide ions F is substituted by the Cl and Br ions with femtosecond laser effect. Even the significant enhancement of Sm2+luminescence is observed in the high halide ions Cl/Br doped samples. Structure anaylisis by TEM measurement indicates that the nanophase containing halide ions Cl or Br is precipited from the glass matrix and Sm3+is selectively incooperated into the nanophase by the femtosecond laser irradiatin effect. Besides, the reduction ability in Br substituted samples is stronger than Cl substituted galsses and both stronger than fluorate galsses. And the electronegativity effect is the proposed for the phenomenon. The lower of the electronegativity value, the ability of drawing electrons is stronger and the reduction ability is higher. Therefore, the external effect on the galss structure is another efficient method for the control of rare earth ions luminescence properties.更多还原