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Tm3+/Yb3+及Ho3+/Yb3+共掺钪酸盐氧化物材料发光性质的研究
李静
学位类型博士
导师张家骅
2014-07
学位授予单位中国科学院大学
学位专业凝聚态物理
摘要对稀土离子上转换现象的研究始于上世纪50年代,在过去的几十年里,人们对上转换发光机理进行了深入的分析,并且随着泵浦源、转换材料的发展,稀土上转换发光已经覆盖了整个可见光波段,而且在双频上转换三维立体显示、硅太阳能电池、防伪标记、固体激光器以及生物标记与医学成像等领域均显示出其广泛的应用前景。钪酸钙(CaSc2O4)由于具有较低的声子能量、较强的晶场、较近的原子距离以及较好的物理特性和化学稳定性,是一类非常优秀的上转换发光基质材料。 本论文以稀土离子激活的新型氧化物材料CaSc2O4为研究对象,系统的研究了Tm3+/Yb3+及Ho3+/Yb3+在该基质材料中的上转换发光特性及其动力学原理,并发现了CaSc2O4: Tm3+/Yb3+中强的下转换发光现象,此外制备了有益于生物医学应用的亚微米级CaSc2O4和β-NaGdF4材料。具体研究内容及结果如下: 1. 研究新型氧化物材料CaSc2O4: Tm3+/Yb3+的上转换发光性质及其动力学原理。在CaSc2O4基质材料中,通过改变掺杂离子Tm3+及Yb3+的浓度,研究离子浓度对上转换发光强度、光谱分布以及能量传递速率的影响。在红外光谱区间(1000 ~ 1750 nm),随着Yb3+浓度的增加,Yb3+离子980 nm发射在Yb3+浓度为5%时达到最大值,而Tm3+离子1600 nm发射在Yb3+浓度为15%时达到最大值。随着Tm3+浓度的增加,Yb3+ 980 nm发射单调下降,表明材料中发生了有效的Yb3+到Tm3+能量传递。光谱显示:Tm3+ 1600 nm与 Yb3+ 980 nm发射的强度比正比于Yb3+浓度的平方,并且与Tm3+浓度成线性关系。结合稳态速率方程可知:第一步能量传递速率W1 = C1n0(N0)2。在可见光谱区间,Tm3+离子480 nm 和800 nm发射的最佳Yb3+浓度为10%,最佳Tm3+浓度为0.4%。实验测得光谱分布随浓度变化的规律与理论分析基本符合。此外,与浓度最优的典型氧化物材料Y2O3: 0.004Tm3+, 0.1Yb3+材料相比,浓度最优CaSc2O4: 0.004Tm3+, 0.1Yb3+样品展示了更强的上转换发光亮度,其中Tm3+近红外(800 nm)和蓝光(480 nm)发射分别增强了3.5和2.2倍。增强的上转换发光来源于CaSc2O4材料中Yb3+离子对980 nm光子拥有更大的吸收截面以及Yb3+到Tm3+第一步能量传递系数(C)更大、能量传递效率更高。 2. 研究新型氧化物材料CaSc2O4: Ho3+/Yb3+的上转换发光性质及其动力学原理。在CaSc2O4: xHo3+,yYb3+系列材料中,优化出最佳掺杂离子浓度分别为x = 0.2%, y = 10%。最佳样品CaSc2O4: 0.2%Ho3+,10%Yb3+展现出良好的绿光单色性(Sgr = 0.85),显示出其在多重荧光探针方面的应用前景。利用光谱分布、衰减曲线、泵浦能量的依赖性等方法深入的探讨了CaSc2O4: Ho3+,Yb3+材料的上转换发光机制。Ho3+离子绿光和近红外发射的强度比不随激发波长和掺杂浓度的变化而变化,说明他们来自于同一能级(5F4 + 5S2),其泵浦路径为Yb3+: 2F5/2 + Ho3+: 5I6 → Yb3+: 2F7/2 + Ho3+: (5F4 + 5S2);Ho3+红光上转换发射来自于5F5能级,该能级通过5I6 → 5I7的无辐射跃迁及随后的Yb3+: 2F5/2 + Ho3+: 5I7 → Yb3+: 2F7/2 + Ho3+: 5F5的能量传递被布局。理论分析结果与实验数据基本吻合。另外,与浓度最优的典型氧化物材料Y2O3: 0.2%Ho3+, 10%Yb3+相比,浓度最优CaSc2O4: 0.2%Ho3+, 10%Yb3+样品展示了更强的上转换发光亮度,其中Ho3+离子绿光(545 nm)和红光(660 nm)发射分别增强了2.6和1.6倍。发光增强的原因为,CaSc2O4样品中Yb3+离子对980 nm光子的吸收能力更强,并且存在更有效的Yb3+到Ho3+能量传递。测量得到CaSc2O4: 0.2%Ho3+,10%Yb3+样品的能量传递效率为50%。 3. 采用溶剂热和退火相结合的方法合成亚微米级棒状CaSc2O4: Tm3+/Yb3+材料。系统的研究了退火温度和时间对样品形貌和晶体结构的影响。与采用传统高温固相法合成的体材料相比,此方法制备的样品形貌规则、分散性好、尺寸小、发光性能良好,有利于其在生物荧光探针及生物成像等方面的应用。退火样品发光亮度可以达到体材料的1.5 ~ 2倍。 4. 采用简易的一步水热法制备具有六棱柱、六棱片、纺锤体以及球形等不同形貌的亚微米级纯相β-NaGdF4材料。系统的研究了前驱溶液的pH值以及采用螯合剂种类对形貌和晶体结构的影响。研究了Tm3+/Yb3+及Ho3+/Yb3+离子在不同形貌样品中的上转换发光性质,其中具有高结晶性的六棱形貌样品发光最强。利用测得的光谱分布和泵浦能量的依赖性,研究了其中的上转换发光机制。 5. 利用高温固相法制备CaSc2O4: 0.2%Tm3+/xYb3+系列样品,研究其下转换发光性质。在Yb3+: 2F5/2 → 2F7/2发射的激发谱中存在位于466 nm处 Tm3+: 3H6 → 1G4吸收峰。用466 nm激发Tm3+: 1G4 能级,除了Tm3+自身发射,还发现强的Yb3+: 2F5/2 → 2F7/2发射带。证明在CaSc2O4材料中,Tm3+: 1G4 → Yb3+: 2F5/能级之间存在有效的能量传递。获得最高能量传递效率 71%,理论最高量子效率171%。
其他摘要The study on upconversion luminescence (UCL) of rare earth (RE) ions doped materials began in 1950s. The UCL properties of RE doped materials have been studied extensively over the past few decades because of the interesting physics research as well as the potential applications in solid-state lasers, high resolution display, biological labeling, infrared imaging, and diagnosis and therapy of diseases and so on. CaSc2O4 is a kind of promising oxide hosts because of the low cutoff phonon frequency, strong crystal field, near atom distance, as well as stable chemical and thermal properties. This thesis mainly focuses on the rare earth ions activated CaSc2O4 oxide material. We research upconversion properties and dynamics study in Tm3+/Yb3+ and Ho3+/Yb3+ codoped CaSc2O4 oxide material in detail. The efficient quantum cutting process is found in CaSc2O4: Tm3+/Yb3+ material. Furthermore, we have synthesized the CaSc2O4: Tm3+/Yb3+submicro-rods in favor of application in biological assays and medical image. The major results obtained are as following: 1. We research the doped concentration dependence of spectral distribution and discuss upconversion dynamics in Tm3+ and Yb3+ codoped CaSc2O4 material. In the infrared emission spectra from 1000 nm to 1750 nm, Yb3+ emission reaches the maximum when Yb3+ concentration reaches to 5%, and Tm3+ 1600 nm emission gradually enhances when Yb3+ concentration increases from 1% to15%. With Tm3+ concentration increasing, Yb3+ emission has amonotonic decline. It can be considered as the indication of efficient Yb3+ → Tm3+ energy transfer. In the UCL spectrum, for 480 nm and 800 nm emissions of Tm3+ ions, the optimized Yb3+ concentration and Tm3+ concentration is 10% and 0.4%, respectively. Compared with that in dopant concentration optimized Y2O3: 0.004Tm3+/0.1Yb3+, furthermore, the UCL around 800 nm and 480 nm in CaSc2O4: 0.004Tm3+/0.1Yb3+ are enhanced by a factor of 3.5 and 2.2, respectively. The UCL enhancement is attributed to a large absorption cross section at 980 nm of Yb3+ and Yb3+ → Tm3+ first step energy transfer coefficient. 2. We research the doped concentration dependence of spectral distribution and discuss upconversion dynamics in Ho3+ and Yb3+ codoped CaSc2O4 material. The CaSc2O4: 0.2%Ho3+, 10%Yb3+ sample has been optimized for the strongest green UCL. And it presents the perfect green monochromaticity as Sgr = 0.85, which favours the simultaneous tracking of multiple fluorescent probes. The studies of spectral distribution, power dependence, and lifetime measurement reveal the UCL mechanism involved in CaSc2O4: Ho3+/Yb3+ material. Furthermore, we found a large enhancement of UCL in concentration optimized CaSc2O4: 0.2%Ho3+/10%Yb3+. UCL intensities around 545 nm and 660 nm are enhanced by a factor of 2.6 and 1.6 by comparison with that in concentration also optimized Y2O3: 0.2%Ho3+/10%Yb3+, respectively. The larger absorption cross section at 980 nm of Yb3+ and Yb3+ → Ho3+ efficient energy transfer play an important role for achievement of intense UCL in CaSc2O4 phosphor. The measured energy transfer efficiency reaches up to 50% for CaSc2O4: 0.2%Ho3+, 10%Yb3+. 3. CaSc2O4: Tm3+/Yb3+ submicro-rods were synthesized using the mild solvothermal and annealing technique. The phase structures, morphologies, and UCL properties of bulk and submicro-rod CaSc2O4: Tm3+/Yb3+ samples were measured and investigated. The synthesized CaSc2O4: Tm3+/Yb3+ sample possesses the characteristics of small size, remarkable monodispersity, and low synthesis temperature, compared with that prepared using conventional solid state reaction method. It also exhibits the stronger UCL than solid state reaction sample. The enhancement factor approaches to 2 for 800 nm emission. 4. The single phase β-NaGdF4 submicron crystal phosphors were synthesized using the mild hydrothermal technique by one-step procedure. The pH value and chelators (EDTA and citric acid) has a crucial effect on the formation of morphology of β-NaGdF4 sample. The UCL properties for the Tm3+/Yb3+ or Ho3+/Yb3+ codoped samples synthesized were researched under 980 nm excitation. The hexagonal prisms that meaning high degree crystallinity demonstrated strong UCL in comparison with other morphologies such as spindles and spheres. By the spectral distribution and power dependence, UCL mechanism is revealed in β-NaGdF4: Tm3+/Yb3+ material. 5. The series of CaSc2O4: 0.2%Tm3+/x%Yb3+ powder samples were synthesized by a solid state reaction. An efficient near infrared quantum cutting has been demonstrated. Upon excitation of Tm3+: 1G4 level with a blue photon at 466 nm, Yb3+: 2F5/2 level can emit two NIR photons around 1000 nm through cooperative ET from Tm3+ to Yb3+. The estimated maximum energy transfer efficiency (ηETE) from Tm3+ to Yb3+ is 71%. The theoretical quantum efficiency (ηTQE) reaches up to 171%. It indicates the presence of Tm3+ → Yb3+ efficient energy transfer.
语种中文
文献类型学位论文
条目标识符http://ir.ciomp.ac.cn/handle/181722/41426
专题中科院长春光机所知识产出
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李静. Tm3+/Yb3+及Ho3+/Yb3+共掺钪酸盐氧化物材料发光性质的研究[D]. 中国科学院大学,2014.
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