【作者】 肖思国；

【导师】 颜晓红；

【作者基本信息】 湘潭大学 ， 凝聚态物理， 2006， 博士

【摘要】 千百年来，人们对一些有着令人着迷的奇特发光现象的天然矿石始终怀着执着的追求，将这些发光矿石称为“宝石”，以拥有并缀饰着它们来显耀自身的身价。这种对发光矿石的膜拜促进了人们对发光材料的认识、加工和研究。随着发光学理论的建立和发展，开发具有特定应用价值的发光材料成为可能。稀土化合物材料作为其中研究最广、性能优异的发光材料在二十世纪七、八十年代才曾是材料学和物理学的研究热点之一。近年来，材料的纳米化使材料在尺寸、结构畸变、局域化等方面形成了新的丰富的物理特性。这使得发光材料超微化、纳米化及其对发光特性与机制的影响的研究成为发光物理新的研究热点。稀土掺杂超微和纳米发光材料也成为该热点研究领域的重要部分。本论文着重研究稀土掺杂纳米化合物材料的光致上转换发光现象，分析纳米效应导致的稀土离子光谱特性与发光机制的特殊影响，探索发展一些可推广工业化生产的稀土掺杂超微化合物材料的制备方法，取得了一些重要进展。用共沉淀法制备Er³⁺掺杂纳米Y₂O₃材料，研究了这种材料在808nm和488nm激光激发下的上转换发光。在808nm激光激发下，⁴F_9/2→⁴I_15/2和²H_11/2、⁴S_3/2→⁴I_15/2上转换发射带的荧光强度均随激发功率的增加，但前者快于后者。基于速率方程分析认为，能量传递过程⁴I_9/2+⁴I_11/2→⁴F_9/2+⁴I_13/2是导致红光随激发功率增加而增加要快于绿光随激发功率增加而增加的根本原因。Er³⁺掺杂纳米Y₂O₃材料在488nm激光激发下出现了多个上转换发射带。最强的上转换荧光带中心波长位于406nm，对应着²P_3/2→⁴I_13/2的辐射跃迁，为两光子过程。我们的研究表明，发展Er³⁺掺杂纳米Y₂O₃陶瓷材料以实现可见到紫外上转换的四能级激光运转系统将是一个可行方案。采用燃烧法制备了不同尺寸的Er³⁺掺杂Y₂O₃粉体材料，系统地研究了尺寸效应对Er³⁺掺杂纳米Y₂O₃材料对Er³⁺离子发光特性的影响。对488nm激光激发下的发射谱的分析发现，随着样品颗粒尺寸的减少，⁴S_3/2能级和^H_11/2能级向基态发射的强度比减少，分析认为属于超敏跃迁的²H_11/2能级与基态的荧光发射几率随粒子尺寸的减少而增加的幅度要大于⁴S_3/2能级向基态的发射。对518nm激发下554nm的荧光衰减曲线的测试和分析发现，处于⁴S_3/2激发态的Er³⁺离子对之间的上转换能量传递几率随粒子尺寸的减少而增加。在980nm激光激发下，随着粒子尺寸减少，上转换强度下降，而上转换红绿荧光强度比随粒子尺寸的减少而增加。对980nm激光激发下的上转换发光研究还发现，随着粒子尺寸减少，“饱和”效应增强。制备出了微晶体的尺寸大约在10-12nm范围的Er³⁺，Yb³⁺共掺氟氧化物透明纳米微晶玻璃。相对于玻璃样品，氟氧化物纳米微晶玻璃的上转换发光强度明显提高，纳米微晶玻璃中²H_11/2，⁴S_3/2→⁴I_15/2的绿色荧光和⁴F_9/2→⁴I_15/2的红色荧光强度相对于氟氧化物玻璃分别提高25倍和6倍。氟氧化物纳米微晶玻璃相对于氟氧化物玻璃，红、绿强度比发生了明显改变；分析认为纳米微晶体基质声子能量的降低和稀土粒子的聚集作用是导致纳米微晶玻璃上转换光谱特性的变化和上转换光强提高的主要原因。采用共沉淀法制备了Er³⁺掺杂和Er³⁺／Yb³⁺共掺杂LaF₃超微材料，所制备的样品的颗粒呈球形，尺寸为250nm左右。Er³⁺单掺杂样品中⁴S_3/2能级和⁴F_9/2能级的量子效率分别达到67.0％和71.9％。Yb³⁺的引入极大地提高了上转换强度。分析发现，当Yb³⁺离子浓度增加，不仅上转化敏化特性发生变化，也使得Er³⁺-Er³⁺离子间相互作用增强，并导致了Er³⁺离子上转换荧光带的强度分布特性改变。首次采用燃烧-氟化法成功合成了Yb³⁺／Er³⁺和Yb³⁺／Tm³⁺共掺杂的氟化镥超微材料，所制备的粒子尺寸约为210nm。研究了该材料在980 nm激光激发下的上转换发光，观测到了对应着Er³⁺离子的7种辐射跃迁的5个荧光带以及对应着Tm³⁺离子的8种辐射跃迁的5个荧光带。所制备的Yb³⁺／Tm³⁺共掺杂的氟化镥超微材料具备良好的上转换蓝光发射特性。基于速率方程理论分析，认为Yb³⁺对Tm³⁺离子的直接合作敏化上转换机制是实现Tm³⁺离子上转换的主要途径。更多还原

【Abstract】 For thousands of years, people have been in persistent pursuit of some fascinatingluminescent natural ores. They call these ores "gems" and take pride in possessing andwearing them as ornaments to show off their wealth and social status. The high evaluation ofluminescent ores has helped to promote people’s recognition, processing and exploration ofluminescent materials. With the establishment and the development of the theory ofluminescence, it has been possible to exploit luminescent materials with certain practicalvalues. Rare earth compounds, with their excellent properties, became one of the host spots inthe research fields of physics and material science in 1970s and 1980s. In recent years,nanonization has caused materials to form abundant new physic properties in size, structuredeformation and localization. This has led the investigation of the superfine and nanomaterials as well as the nano effect on luminescent properties and mechanisms to become newhot spots of luminescent physics, of which the investigation of rare earth doped superfine andnano materials constitutes important part. In this PHD dissertation, the up-conversion of rareearth doped nano compounds and the nano effect on spectral properties and luminescentmechanisms are investigated. Several preparation methods of rare earth doped superfineluminescent compounds which might be industrialized are explored. Some important progressis made.Er³⁺ doped Y₂O₃ nano crystal is prepared with co-precipitation method. The up-conversionluminescence properties of Er³⁺ doped Y₂O₃ nano crystal with excitation of 808 nm and 488nm are investigated, respectively. It is found that under 808 um excitation the up-convertedred emission intensity of ⁴F_9/2→⁴I_15/2 transition increases upon the excitation power morequickly than that of the green emission of ²H_11/2(⁴S_3/2)→⁴I_15/2 transition. Based on rateequation, the up-conversion mechanism is discussed. It is believed that no-resonant energytransfer of ⁴I_9/2+⁴I_11/2—⁴F_9/2+⁴I_13/2 play an important role in performing the redup-conversion emission, resulting that the red emission intensity increases upon the excitationpower more quickly than that of the green emission. Under 488 nm excitation, Er³⁺ dopedY₂O₃ nano crystal, Multiple up-converted emissions have been observed. The most intenseup-converted emission centered at 406 um, which corresponds to the ²p_3/2→⁴I_13/2 transition,is a two-photon process. Our investigation suggests that realization of violet laser operationby a four-level system might be a feasible approach by developing Er³⁺:Y₂O₃ nano-crystalline ceramics.Er³⁺ doped Y₂O₃ nano crystals with different size are prepared using combustion method.Size effect on luminescence properties of Er³⁺ doped Y₂O₃ nano crystals is investigated. Theemission spectra under 488 nm excitation indicate that the ratio of the intensity of ⁴S_3/2→⁴I_15/2transition to that of ²H_11/2→⁴I_15/2 decreases with the decrease of the particle size. It is believedthat the rate of hypersensitive transition of ²H_11/2→⁴I_15/2 increases with the decrease of theparticle size more quickly than that of transition of ⁴S_3/2→⁴I_15/2. The time dependence of the554 nm luminescence decay excited by 518 nm reveals that the rate of up-converting energytransfer occurring between two Er³⁺ ions in ⁴S_3/2 state increases with the decrease of theparticle size. The up-conversion luminescence of Er³⁺ doped Y₂O₃ nano crystals with differentsize pumped at 980 nm is investigated. As the particle size decreases, "saturation effect"becomes more serious.Transparent Er³⁺/Yb³⁺ co-doped oxyfluoride glass ceramics is prepared, which containsnano crystalline with size of 10-12 nm. The up-conversion emission in oxyfluoride glassceramics is notably stronger than that in its glass counterpart. The green luminescenceintensity of the ²H_11/2(⁴S_3/2)→⁴I_15/2 transition and the red luminescence intensity of ⁴F_9/2→⁴I_15/2 transition in the glass ceramics are 26 and 6 times stronger than those in its glasscounterpart, respectively. The ratio of the red emission intensity to the green one also changesobviously. It is believed that the low phonon energy in nano crystalline and the assemblingeffect result in the enhancement of the up-conversion emission and the change of theup-conversion properties.Er³⁺ doped and Er³⁺/Yb³⁺ co-doped superfine LaF₃ powders are prepared usingco-precipitation method. The sample shows sphere like particle with siz of about 250 nm. Thequantum efficiencies of ⁴S_3/2 and ⁴F_9/2 levels in Er³⁺ doped LaF₃ powders are 67.0% and71.9%, respectively. The introduction of Yb³⁺ largely improves the up-conversion intensity.With the enhancement of Yb³⁺ concentration the sensitizing properties change. On the otherhand, the Er³⁺-Er³⁺ interaction is reinforced as Yb³⁺ concentration increases. These lead to thevariation of the intensity distribution among the up-converted emission bands.Er³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ co-doped superfine powders are prepared with a combustionsynthesis method followed with fluorization process for the first time. The fabricated particlesize is about 210 um. Under 980 nm excitation, five up-converted luminescence bandsattributed to seven transitions of Er³⁺ ion and five up-converted luminescence bands attributedto eight transitions of Tm³⁺ ion are observed. The Tm³⁺/Yb³⁺ co-doped superfine powderspresent strong blue emission. On the basis of rate equation discussion, it is believed that directcooperation sensitization mechanism from Yb³⁺ to Tm³⁺ is a main way performing the up-converted emission.更多还原