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，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（1000~1750nm），随着Yb3+浓度的增加，Yb3+离子980nm发射在Yb3+浓度为5%时达到最大值，而Tm3+离子1600nm发射在Yb3+浓度为15%时达到最大值。随着Yb3+浓度的增加，Yb-Yb和Yb-Tm对的距离减小，使得Yb3+离子之间的能量迁移速率增加，最终加快了Yb3+Tm3+能量传递。随着Tm3+浓度的增加，Yb3+980nm发射单调下降，表明材料中发生了有效的Yb3+Tm3+能量传递。光谱显示：Tm3+1600nm与Yb3+980nm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480nm和800nm发射的最佳Yb3+浓度为10%，最佳Tm3+浓度为0.4%。随Yb3+和Tm3+浓度改变，Tm3+480nm和800nm发射的强度比的变化趋势与Yb3+离子980nm发射强度的变化趋势相同。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（800nm）和蓝光（480nm）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980nm光子拥有更大的吸收截面（）以及Yb3+Tm3+第一步能量传递系数（C）更大、能量传递效率（ET）更高。利用光谱分布和寿命衰减曲线，计算得出：在CaSc2O4材料中，Yb3+的吸收截面（）是其在Y2O3材料中的3倍。在CaSc2O4材料中，初始能量传递系数（C）和能量传递效率（ET）分别为：C=9.29×10-17cm3s-1、 ET=0.7；在Y2O3中，初始能量传递系数（C）和能量传递效率（ET）仅为：C=2.87×10-17cm3s-1、 ET=0.47。
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（545nm）和红光（660nm）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980nm光子的吸收能力更强，并且存在更有效的Yb3+Ho3+能量传递。测量得到CaSc2O4:0.2%Ho3+，10%Yb3+样品的能量传递效率（ET）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。制备样品上转换发光更强，其中Tm3+的近红外发射(800nm)增强了2倍左右。
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466nm处Tm3+:3H6→1G4吸收峰。用466nm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。随着Yb3+浓度的增加，Tm3+发射峰的强度逐渐下降；Yb3+离子发射峰的强度逐渐上升，在Yb3+=5%时达到最高点，随后由于浓度猝灭，强度开始下降。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ETE=71%，理论最高量子效率TQE=171%。
The study on upconversion luminescence (UCL) of rare earth (RE) ions dopedmaterials began in1950s. The UCL properties of RE doped materials have beenstudied extensively over the past few decades because of the interesting physicsresearch as well as the potential applications in solid-state lasers, high resolutiondisplay, biological labeling, infrared imaging, and diagnosis and therapy of diseasesand so on. CaSc2O4is a kind of promising oxide hosts because of the low cutoffphonon frequency, strong crystal feld, near atom distance, as well as stable chemicaland thermal properties.
This thesis mainly focuses on the RE ions activated CaSc2O4oxide material. Weresearch upconversion properties and dynamics study in Tm3+/Yb3+and Ho3+/Yb3+codoped CaSc2O4oxide material in detail. The efficient quantum cutting process isalso found in CaSc2O4: Tm3+/Yb3+material. Furthermore, we have synthesized theCaSc2O4: Tm3+/Yb3+submicro-rods in favor of application in biological assays andmedical image. The major results obtained are as following:
1. We research the doped concentration dependence of spectral distribution anddiscuss upconversion dynamics in Tm3+and Yb3+codoped CaSc2O4material. In theinfrared emission spectra from1000nm to1750nm, Yb3+emission reaches themaximum when Yb3+concentration reaches to5%, and Tm3+1600nm emissiongradually enhances when Yb3+concentration increases from1%to15%. The distancesof Yb-Yb and Yb-Tm pairs decrease with Yb3+concentration increasing, then theenhanced energy migration among Yb3+ions speeds up energy transfer from Yb3+toTm3+. With Tm3+concentration increasing, Yb3+emission has amonotonic decline. Itcan be considered as the indication of effcient Yb3+Tm3+energy transfer. Theintensity ratio of Tm3+1600nm emission to Yb3+980nm emission satisfies aproportional relationship with the Tm3+concentration and exhibits the quadratic dependence on Yb3+concentration. The first step energy transfer rate W1is written asW1=C1n0(N0)2. In the UCL spectrum, for480nm and800nm emissions of Tm3+ions,the optimized Yb3+concentration and Tm3+concentration is10%and0.4%,respectively. The480nm to800nm intensity ratio exhibits the same trend with Yb3+980nm emission intensity. Compared with that in dopant concentration optimizedY2O3:0.004Tm3+/0.1Yb3+, furthermore, the UCL around800nm and480nm inCaSc2O4:0.004Tm3+/0.1Yb3+is enhanced by a factor of3.5and2.2, respectively. TheUCL enhancement is attributed to a large absorption cross section (3times as that inY2O3) at980nm of Yb3+and Yb3+→Tm3+first step energy transfer coefficient(9.29×10-17cm3s-1in CaSc2O4vs2.87×10-17cm3s-1in Y2O3). The Yb3+→Tm3+energytransfer efficiency in CaSc2O4:0.004Tm3+/0.1Yb3+is0.70quite larger than0.47inY2O3:0.004Tm3+/0.1Yb3+.
2. We research the doped concentration dependence of spectral distribution anddiscuss upconversion dynamics in Ho3+and Yb3+codoped CaSc2O4material. TheCaSc2O4:0.2%Ho3+,10%Yb3+sample has been optimized for the strongest greenUCL. And it presents the perfect green monochromaticity as Sgr=0.85, which favoursthe simultaneous tracking of multiple fluorescent probes. The studies of spectraldistribution, power dependence, and lifetime measurement reveal the UCLmechanism involved in CaSc2O4: Ho3+/Yb3+material. The intensity ratio of green toNIR emission does not vary with the excitation wavelengths and doped concentrations.Both emissions have the same time evolutions and pump power dependences under980nm excitation. We conclude the green and NIR emissions come from the sameupper levels (5F4+5S2). The evolution of the green intensity by experiment is in goodagreement with the theoretical calculation basing on infrared spectral distributions,illustrating it is populated via Yb3+:2F5/2+Ho3+:5I6→Yb3+:2F7/2+Ho3+:(5F4+5S2)pathway. The red emitting is from Ho3+:5F5level. The5F5state is populated through5I6→5I7nonradiative relaxation, subsequent Yb3+:2F5/2+Ho3+:5I7→Yb3+:2F7/2+Ho3+:5F5energy transfer. Furthermore, we found a large enhancement of UCL inconcentration optimized CaSc2O4:0.2%Ho3+/10%Yb3+. UCL intensities around545nm and660nm are enhanced by a factor of2.6and1.6by comparison with that inconcentration also optimized Y2O3:0.2%Ho3+/10%Yb3+, respectively. The largerabsorption cross section at980nm of Yb3+and Yb3+→Ho3+efficient energy transferplay an important role for achievement of intense UCL in CaSc2O4phosphor. Themeasured energy transfer efficiency reaches up to50%for CaSc2O4:0.2%Ho3+, 10%Yb3+.
3. CaSc2O4: Tm3+/Yb3+submicro-rods were synthesized using the mildsolvothermal and annealing technique. The phase structures, morphologies, and UCLproperties of bulk and submicro-rod CaSc2O4: Tm3+/Yb3+samples were measured andinvestigated. The synthesized CaSc2O4: Tm3+/Yb3+sample possesses thecharacteristics of small size, remarkable monodispersity, and low synthesistemperature, compared with that prepared using conventional solid state reactionmethod. It also exhibits the stronger UCL than solid state reaction sample. Theenhancement factor approaches to1.5for800nm emission.
4. The single phase β-NaGdF4submicron crystal phosphors were synthesizedusing the mild hydrothermal technique by one-step procedure. The pH value andchelators (EDTA and citric acid) have a crucial effect on the morphology of β-NaGdF4sample. The UCL properties for the Tm3+/Yb3+or Ho3+/Yb3+codoped samplessynthesized were researched under980nm excitation. The hexagonal prisms thatmeaning high degree crystallinity demonstrated the strong UCL in comparison withother morphologies such as spindles and spheres. By the spectral distribution andpower dependence, UCL mechanism is revealed in β-NaGdF4: Tm3+/Yb3+material.
5. The series of CaSc2O4:0.2%Tm3+/x%Yb3+powder samples were synthesizedby a solid state reaction. An efficient near infrared quantum cutting has beendemonstrated. Upon excitation of Tm3+:1G4level with a blue photon at466nm, Yb3+:2F5/2level can emit two NIR photons around1000nm through cooperative ET fromTm3+to Yb3+. The estimated maximum energy transfer efciency (ηETE) from Tm3+toYb3+is71%. The theoretical quantum efciency (ηTQE) reaches up to171%. The Tm3+:3H6→1G4absorption around466nm is observed by monitoring Yb3+:2F5/2→2F7/2emission. Under466nm excitation corresponding to Tm3+:3H6→1G4transition, astrong emission band around1000nm assigned to the Yb3+:2F5/2→2F7/2transition isobserved. The emission intensities of Tm3+ion have a decline and NIR emissionintensity of Yb3+ion increases rapidly with Yb3+concentration increasing. For thehigher Yb3+concentration over5%, Yb3+emission is reduced due to concentrationquenching. It indicates the presence of Tm3+→Yb3+efficient energy transfer.
引文
[1]张若桦．稀土元素化学[M]．天津：科学技术出版社，1987.
[2]孙家跃，杜海燕.固体发光材料[M].北京：化学工业出版社，2003
[3] N. Bloemberge. Solid State Infrared Quantum Counters [J]. Phys. Rev. Lett.,1959,2:84.
[4] F. Auzel. Comptes rendus hebdomadaires des seances de Lacademie des [J].Compt. Rend.,1966,263b:819.
[5] F. Auzel. Compteur Quantique Par Transfert Denergie Entre Deux Ions De TerresRares Dans Un Tungstate Mixte Et Dans Un Verre [J]. Compt. Rend.,1966,263b:1016.
[6] L. Esterowitz, J. Noonan, J. Bahler. Enhancement in a Ho3+-Yb3+QuantumCounter by Energy Transfer [J]. Appl. Phys. Lett.,1967,10:126.
[7] V. V. Ovsyankin, P. P. Feofilov. Cooperative Luminescence of Solids [J]. AppliedOptics,1967,6(11):1828-1833.
[8] R. A. Hewes, J. F. Sarver. Infrared Excitation Processes for the VisibleLuminescence of Er3+, Ho3+, and Tm3+in Yb3+–Sensitized Rare-Earth Trifluorides [J].Phys. Rev.,1969,182:427-436.
[9] T. Miyakawa, D. L. Dexter. Cooperative and Stepwise Excitation ofLuminescence: Trivalent Rare-Earth Ions in Yb3+-Sensitized Crystals [J]. Phys. Rev. B,1970,1:70-80.
[10]F. Auzel. Material and device using double-pumped phosphors with energytransfer [J]. Proc. IEEE,1973,61(6):758-760.
[11]徐东勇,臧竞存.上转换激光和上转换发光材料的研究进展[J].人工晶体学报,2001,30:203-210.
[12]F. Heine, E. Heumann, T. Danger, et al. Green Upconversion Continuous WaveEr3+BLiYF4Laser at Room Temperature [J]. Appl. Phys. Lett.,1994,65(4):383-384.
[13]R. H. Page, K. I. Schaffers, P. A. Waide, et al. Upconversion-pumpedluminescence effciency of rare-earth-doped hosts sensitized with trivalent ytterbium[J]. J. Opt. Soc. Am. B,1998,15:996-1008.
[14]E. Downing, L. Hesselink, J. Ralston, et al. A three-color solid-state threedimensional [J]. Science,1996,273:1185-1189.
[15]刘政威，佘仲明.能量上转换功能材料及其制作的防伪标记材料[P].中国专利:ZL00113404.3,2004-2-11.
[16]A. Shalav, B. S. Richards, T. Trupke, et al. Application of NaYF4: Er3+up-converting phosphors for enhanced near-infrared silicon solar cell response [J].Appl. Phys. Lett.,2005,86:013505.
[17]S. F. Lim, R. Riehn, W. S. Ryu, et al. In Vivo and Scanning Electron MicroscopyImaging of Upconverting Nanophosphors in Caenorhabditis elegans [J]. Nano Lett.,2006,6:169-174.
[18]F. Wang, X. G. Liu. Recent advances in the chemistry of lanthanide-dopedupconversion nanocrystals [J]. Chem. Soc. Rev.2009,38:976-989.
[19]杨建虎,戴世勋,姜中宏.稀土离子的上转换发光及研究进展[J].物理学进展,2003,23:284-298.
[20]R. P. Feynman. There is plenty of room at the bottom, Lecture at the annualmeeting of the American Physical Society at the California Institute of Technology[R].1959.
[21]张立德，牟季美.纳米材料和纳米结构[M].第一版，北京：科学出版社，2001.
[22]段学臣，曾真诚.纳米材料制备法和展望[J].稀有金属和硬质合金，2001.
[23]J. Hampl, M. Hall, N. A. Mufti, et al. Upconverting phosphor reporters inimmunochromatographic assays [J]. Anal. Biochem.,2001,288:176-187.
[24]G. S. Yi, H. C. Lu, S. Y. Zhao, et al. Synthesis, Characterization, and BiologicalApplication of Size-Controlled Nanocrystalline NaYF4: Yb, Er Infrared-to-VisibleUp-Conversion Phosphors [J]. Nano Lett.,2004,4:2191.
[25]H. Mai, Y. Zhang, R. Si, et al. High-Quality Sodium Rare-Earth FluorideNanocrystals: Controlled Synthesis and Optical Properties [J]. J. Am. Chem. Soc.,2006,128:6426-6436.
[26]J. C. Boyer, L. A. Cuccia, J. A. Capobianco. Synthesis of Colloidal UpconvertingNaYF4: Er3+/Yb3+and Tm3+/Yb3+Monodisperse Nanocrystals [J]. Nano Lett.,2007,7:847-852.
[27]G. Yi, G. Chow. Colloidal LaF3:Yb, Er, LaF3:Yb, Ho and LaF3:Yb, Tmnanocrystals with multicolor upconversion fluorescence [J]. J. Mater. Chem.,2005,15:4460-4464.
[28]J. L. Sommerdijk, A. Bril, de Jager A W. Two phonton luminescence withultraviolet excitation of trivalent praseodymium [J]. J Lumin.,1974,8:341-343.
[29]W. W. Piper, de Luca J A, F. S. Ham. Cascade fluorescent decay in Pr3+-dopedfluorides: achievement of a quantum yield greater than unity for emission of visiblelight [J]. J Lumin.,1974,8:344-348.
[30]R. T. Wegh, H. Donker, K. D. Oskam, et al. Visible quantum cutting in LiGdF4:Eu3+through downconversion, Science,1999,283:663-666.
[31]P. Vergeer, T. J. H. Vlugt, M. H. F. Kox, et al. Quantum cutting by cooperativeenergy transfer in YbxY1xPO4: Tb3+[J]. Phys. Rev. B,2005,71:014119.
[32]W. Shockley, H. Queisser. Detailed balance limit of efficiency of p-n junctionsolar cells [J]. J Appl. Phys,1961,32:510-519.
[33]van der Ende B M, L. Aarts, A. Meijerink. Near-Infrared Quantum Cutting forPhotovoltaics [J]. Adv. Mater.2009,21:3073-3077.
[34]van der Zwaan B, A. Rabl. Prospects for PV: a learning curve analysis [J]. Sol.Energy2003,74:19-31.
[35]B. S. Richards. Enhancing the performance of silicon solar cells via theapplication of passive luminescence conversion layers [J]. Sol Energy Mater Sol Cells,2006,90:2329-2337.
[36]B. S. Richards. Luminescent layers for enhanced silicon solar cell performance:Down-conversion [J]. Sol Energy Mater Sol Cells,2006,90:1189-1207.
[37]J. Li, J. H. Zhang, X. Zhang, et al. Cooperative downconversion and near infraredluminescence of Tm3+/Yb3+codoped Calcium Scandate phosphor [J]. Journal ofAlloys and Compounds,2014,583:96-99.
[38]M. M. Smedskjaer, J. Qiu, J. Wang, et al. Near-infrared emission from Eu-Ybdoped silicate glasses subjected to thermal reduction [J]. Appl. Phys. Lett.,2011,98:071911.
[39]Q. Y. Zhang, G. Y. Yang. Cooperative downconversion in GdAl3(BO3)4: RE3+,Yb3+(RE=Pr, Tb, and Tm)[J]. Appl. Phys. Lett.,2007,91:051903.
[40]S. Ye, B. Zhu, J. X. Chen, et al. Infrared quantum cutting in Tb3+,Yb3+codopedtransparent glass ceramics containing CaF2nanocrystals [J]. Appl. Phys. Lett.,2008,92:141112.
[41]J. J. Eilers, D. Biner, Wijngaarden J T van, et al. Efficient visible to infraredquantum cutting through downconversion with the Er3+-Yb3+couple in Cs3Y2Br9[J].Appl. Phys. Lett.,2010,96:151106.
[42]N. Rakov, G. S. Maciel. Near-infrared quantum cutting in Ce3+, Er3+, and Yb3+doped yttrium silicate powders prepared by combustion synthesis [J]. J Appl. Phys.,2011,110:083519.
[43]张思远,毕宪章.稀土光谱理论[M].长春:吉林科学技术出版社，1991.第2章，第9章。
[44]黄世华.离子中心的发光动力学[M].第一版,北京:科学出版社,2002. p5.
[45]李建宇.稀土发光材料及其应用[M].北京：化学工业出版社，2003.
[46]T. F rster. Experimentelle und theoretische Untersuchung deszwischenmolekularen übergangs von Elektronen-anregungsenergie [J]. ZNaturforschung,1949,4a:321.
[47]D. L. Dexter. A theory of sensitized luminescence in solids [J]. J. Chem. Phys.,1953,21:836-850.
[48]S. Shionoya, W. M. Yen. Phosphor Handbook [M], New York:CRC Press,2000,109-112.
[49]M. F. Joubert. Photon avalanche upconversion in rare earth laser materials [J].Opt. Mat.,1999,11:181-203.
[50]M. Pollnau, D. R. Gamelin. Power dependence of upconversion luminescence inlanthanide and transition-metal-ion systems [J]. Phys. Rev. B,2000,61:3337-3346.
[51]D. L. Dexter. Possibility of luminescent quantum yields greater than unity. PhysRev.,1957,108:630-633.
[52]T. T. Basiev, M. E. Doroshenko, V. V. Osiko. Cooperative nonradiativecross-relaxation in crystals of La(1x)CexF3solid solutions [J]. JETP Lett.,2000,71:8-11.
[53]T. T. Basiev, I. T. Basieva, M. E. Doroshenko, et al. Cooperative quenching:experiment, theory and Monte-Carlo computer simulation [J]. J. Lumin.,2001,94:349-354.
[54]I. T. Basieva, K. K. Pukhov, T. T. Basiev. Cooperative quenching kinetics:Theoryand Monte-Carlo simulation [J]. JETP Lett.,2001,74:539-542.
[55]L. Xie, Y. H. Wang, H. J. Zhang. Near-infrared quantum cutting in YPO4:Yb3+,Tm3+via cooperative energy transfer [J]. Appl. Phys. Lett.,2009,94:061505.
[56]J. R. Carter, R. S. Feigelson. Preparation and Crystallographic Properties ofA2+B23+O4Type Calcium and Strontium Scandates [J]. Journal of The AmericanCeramic Society-Carter and Feigelson,1964,47:141-144.
[57]李艳平.稀土激活的LuBO3、Lu2O3纳米材料的制备与发光性质:[博士学位论文].北京:中科院研究生院,2010.
[58]金叶. Eu3+掺杂的纳米磷酸盐及Sm3+、Eu3+共掺的钼酸盐合成、发光特性研究:[博士学位论文].北京:中科院研究生院,2010.
[59]郝振东.近紫外基白光LED用Ca2P2O7:Eu2+, Mn2+及CaSc2O4:Eu3+荧光粉发光特性的研究.:[博士学位论文].北京:中科院研究生院,2009.
[60]S. H. Huang. The principles and methods of laser spectroscopy [M]. JilinUniversity Press,2001.
[61]Z. G. Chen, H. L. Chen, H. Hu, et al. Versatile Synthesis Strategy for CarboxylicAcid-functionalized Upconverting Nanophosphors as Biological Labels [J]. J. Am.Chem. Soc.,2008,130:3023-3029.
[62]M. Nyk, R. Kumar, T. Y. Ohulchanskyy, et al. High Contrast in Vitro and in VivoPhotoluminescence Bioimaging Using Near Infrared to Near Infrared Up-Conversionin Tm3+and Yb3+Doped Fluoride Nanophosphors [J]. Nano Lett.,2008,8:3834-3838.
[63]S. Schietinger, T. Aichele, H. Q. Wang, et al. Plasmon-Enhanced Upconversion inSingle NaYF4:Yb3+/Er3+Codoped Nanocrystals [J]. Nano Lett.,2010,10:134-138.
[64]F. Auzel. Upconversion and Anti-Stokes Processes with f and d Ions in Solids [J].Chem. Rev.,2004,104:139-174.
[65]H. T. Wong, H. L. W. Chan, J. H. Hao. Towards pure near-infrared tonear-infrared upconversion of multifunctional GdF3:Yb3+, Tm3+Nanoparticles [J]. Opt.Express,2010,18:6123-6130.
[66]B. Dong, B. S. Cao, Y. Y. He, et al. Temperature Sensing and In Vivo Imaging byMolybdenum Sensitized Visible Upconversion Luminescence of Rare-Earth Oxides[J]. Adv. Mater.,2012,24:1987-1993.
[67]I. Etchart, A. Huignard, M. Bérard, et al. Oxide phosphors for effcient lightupconversion: Yb3+and Er3+co-doped Ln2BaZnO5(Ln=Y, Gd)[J]. J. Mater. Chem.,2010,20:3989-3994.
[68]Y. Shimomura, T. Kurushima, N. Kijima. Photoluminescence and CrystalStructure of Green-Emitting Phosphor CaSc2O4: Ce3+[J]. J. Electrochem. Soc.,2007,154: J234-J238.
[69]Z. D. Hao, J. H. Zhang, X. Zhang, et al. Blue-Green-Emitting PhosphorCaSc2O4:Tb3+: Tunable Luminescence Manipulated by Cross-Relaxation [J]. J.Electrochem. Soc.,2009,156: H193-H196.
[70]Z. D. Hao, J. H. Zhang, X. Zhang, et al. CaSc2O4: Eu3+: A tunable full-coloremitting phosphor for white light emitting diodes [J]. Opt. Mater.,2011,33:355-358.
[71]R. D. Shannon. Revised Effective Ionic Radii and Systematic Studies ofInteratomie Distances in Halides and Chaleogenides [J]. Acta Crystallogr.,1976,32:751-767.
[72]R. Gaume, B. Viana, J. Derouet, et al. Spectroscopic properties of Yb-dopedscandium based compounds Yb: CaSc2O4, Yb: SrSc2O4and Yb: Sc2SiO5[J]. Opt.Mater.,2003,22:107-115.
[73]M. M. Broer, D. L. Huber, W. M. Yen, et al. Resonant Fluorescence LineNarrowing in La1-xP5O14: Ndx3+[J]. Phys. Rev. Lett.,1982,49:394-397.
[74]L. Laversenne, Y. Guyot, C. Goutaudier, et al. Optimization of spectroscopicproperties of Yb3+-doped refractory sesquioxides: cubic Y2O3, Lu2O3and monoclinicGd2O3[J]. Opt. Mater.,2001,16:475-483.
[75]F. W. Ostermayer, Jr., J. P. van der Ziel, et al. Frequency Upconversion in YF3:Yb3+, Tm3+[J]. Phys. Rev. B,1971,3:2698-2705.
[76]Q. Y. Zhang, T. Li, Z. H. Jiang, et al.980nm laser-diode-excited intense blueupconversion in Tm3+/Yb3+-codoped gallate–bismuth–lead glasses [J]. Appl. Phys.Lett.,2005,87:171911.
[77]B. Peng, T. Izumitani. Blue, green and0.8μm Tm3+, Ho3+doped upconversionlaser glasses, sensitized by Yb3+[J]. Opt. Mater.,1995,4:701-711.
[78]F. Lahoz, I. R. Martín, J. Méndez-Ramos. Dopant distribution in a Tm3+-Yb3+codoped silica based glass ceramic: An infrared-laser induced upconversion study [J].J. Chem. Phys.,2004,120:6180-6190.
[79]A. Braud, S. Girard, J. L. Doualan, Energy-transfer processes in Yb: Tm-dopedKY3F10, LiYF4, and BaY2F8single crystals for laser operation at1.5and2.3μm [J].Phys. Rev. B,2000,61:5280-5295.
[80]M. A. Noginov, M. Curley, P. Venkateswarlu, Excitation scheme for the upperenergy levels in a Tm:Yb:BaY2F8laser crystal [J]. J. Opt. Soc. Am. B,1997,14:2126-2136.
[81]X. X. Zhang, P. Hong, M. Bass, Blue upconversion with excitation into Tm ionsat780nm in Yb-and Tm-codoped fluoride crystals [J]. Phys. Rev. B,1995,51:9298-9301.
[82]S. G. Xiao, X. L. Yang, J. W. Ding, Up-Conversion in Yb3+-Tm3+Co-DopedLutetium Fluoride Particles Prepared by a Combustion-Fluorization Method [J]. J.Phys. Chem. C,2007,111:8161-8165.
[83]D. A. Simpson, W. E. K. Gibbs, S. F. Collins. Visible and near infra-redup-conversion in Tm3+/Yb3+co-doped silica fibers under980nm excitation [J]. Opt.Express,2008,16:13781-13799.
[84]F. Pandozzi, F. Vetrone, J. Boyer. A Spectroscopic Analysis of Blue andUltraviolet Upconverted Emissions from Gd3Ga5O12: Tm3+, Yb3+Nanocrystals [J]. J.Phys. Chem. B,2005,109:17400.
[85]I. Etchart, I. Hernández, A. Huignard. Oxide phosphors for light upconversion;Yb3+and Tm3+co-doped Y2BaZnO5[J]. J. Appl. Phys.,2011,109:063104.
[86]Y. Mita, M. Togashi, Y. Umetsu. Energy Transfer Processes in Yb3+-andTm3+-Ion-Doped Oxide and Fluoride Crystals [J]. Jpn. J. Appl. Phys.,2001,40:5925-5929.
[87]J. Li, J. H. Zhang, Z. D. Hao, et al. Upconversion properties and dynamics studyin Tm3+and Yb3+codoped CaSc2O4oxide material [J]. J. Appl. Phys.,2013,113:223507.
[88]Z. S. Xiao, R. Serna, F. Xu. Critical separation for effcient Tm3+–Tm3+energytransfer evidenced in nanostructured Tm3+: Al2O3thin flms [J]. Opt. Lett.,2008,33:608-610.
[89]S. Guy. Modelization of lifetime measurement in the presence of radiationtrapping in solid-state materials [J]. Phys. Rev. B,2006,73:144101.
[90]J. Li, J. H. Zhang, Z. D. Hao, et al. Intense upconversion luminescence and originstudy in Tm3+/Yb3+codoped calcium scandate [J]. Appl. Phys. Lett.,2012,101:121905.
[91]M. Ito, C. Goutaudier, Y. Guyot. Crystal growth, Yb3+spectroscopy,concentration quenching analysis and potentiality of laser emission in Ca1XYbXF2+X[J]. J. Phys.: Condens. Matter,2004,16:1501-1521.
[92]J. F. Suyver, A. Aebischer, S. García-Revilla. Anomalous power dependence ofsensitized upconversion luminescence [J]. Phys. Rev. B,2005,71:125123.
[93]F. K. Fong, D. J. Diestler. Many-Body Processes in Nonradiative Enery Transferbetween Ions in Crystals [J]. J. Chem. Phys.,1972,56:2875-2880.
[94]D. L. Andrews, R. D. Jenkins. A quantum electrodynamical theory of three-centerenergy transfer for upconversion and downconversion in rare earth doped materials [J].J. Chem. Phys.,2001,114:1089-1100.
[95]E. M. Chan, G. Han, J. D. Goldberg, et al. Combinatorial Discovery ofLanthanide-Doped Nanocrystals with Spectrally Pure Upconverted Emission [J].Nano Lett.,2012,12:3839-3845.
[96]M. J. Dejneka, A. Streltsov, S. Pal, et al. Rare earth-doped glass microbarcodes
[M]. Proc. Natl. Acad. Sci. U.S.A.2003,100:389-393.
[97]E. D. Rosa, P. Salas, H. Desirena, et al. Strong green upconversion emission inZrO2:Yb3+–Ho3+nanocrystals [J]. Appl. Phys. Lett.,2005,87:241912(1-3).
[98]I. R. Martín, V. D. Rodríguez, V. Lavín, et al. Upconversion dynamics inYb3+-Ho3+doped fuoroindate glasses [J]. J.Alloys Compd.,1998,275–277:345-348.
[99]J. Li, Z. D. Hao, X. Zhang, et al. Hydrothermal synthesis and upconversionluminescence properties of β-NaGdF4: Yb3+/Tm3+and β-NaGdF4:Yb3+/Ho3+submicron crystals with regular morphologies [J]. J. Colloid Interf. Sci.,2013,392:206-212.
[100] Y. Yu, Y. Zheng, F. Qin, et al. Infuence of Yb3+concentration onupconversion luminescence of Ho3+[J]. Opt. Comm.,2011,284:1053-1056.
[101] J. Silver, E. Barrett, P. J. Marsh, et al. Yttrium Oxide UpconvertingPhosphors.5. Upconversion Luminescent Emission from Holmium-Doped YttriumOxide under632.8nm Light Excitation [J]. J. Phys. Chem. B,2003,107:9236-9242.
[102] N. M. Sangeetha, F. C. Veggel. Lanthanum Silicate and Lanthanum ZirconateNanoparticles Co-Doped with Ho3+and Yb3+: Matrix-Dependent Red and GreenUpconversion Emissions [J]. J. Phys. Chem. C,2009,113:14702-14707
[103] S. H. Huang, S. T. Lai, L. R. Lou, et al. Upconversion in LaF3:Tm3+[J]. Phys.Rev. B,1981,24(1):59-63.
[104] G. D. Gilliland, R. C. Powell. Spectral and up-conversion dynamics and theirrelationship to the laser properties of BaYb2F8:Ho3+. Phys. Rev. B,1988,38(14):9958-9973.
[105] Y. Yu, Y. Zheng, F. Qin, et al. Experimental investigation on the upconversionmechanism of754nm NIR luminescence of Ho3+/Yb3+:Y2O3,Gd2O3under976nmdiode laser excitation [J]. J. Lumin.,2011,131:190-193.
[106] S. Balaji, A. K. Mandal, K. Annapurna. Energy transfer based NIR to visibleupconversion: Enhanced red luminescence from Yb3+/Ho3+co-doped tellurite glass [J].Opt. Mater.,2012,34:1930-1934.
[107] Y. Q. Sheng, L. L. Xu, J. Liu, et al. Improving monochromaticity ofupconversion luminescence by codoping Eu3+ions in Y2O3:Ho3+, Yb3+nanocrystals[J]. J. Lumin.,2010,130:338-341.
[108] W. F. Peng, S. Y. Zou, G. X. Liu, et al. Combustion synthesis andupconversion luminescence of CaSc2O4:Yb3+, Er3+nanopowders [J]. J. Rare Earths,2011,29:330–334.
[109] J. X. Meng, F. J. Zhang, W. F. Peng, et al. Fluorescence properties of novelnear-infrared phosphor CaSc2O4:Ce3+, Nd3+[J]. J. Alloys Compd.,2010,508:222-225.
[110] J. Li, J. H. Zhang, Z. D. Hao, et al. Synthesis, morphology, and upconversionluminescence of Tm3+/Yb3+codoped bulk and submicro-rod CaSc2O4phosphors [J].Inorg. Chem. Comm.,2013,38:119-122.
[111] Y. Li, J. Zhang, X. Zhang, et al. Near-Infrared to Visible Upconversion inEr3+and Yb3+Codoped Lu2O3Nanocrystals: Enhanced Red Color Upconversion andThree-Photon Process in Green Color Upconversion [J]. J. Phys. Chem. C,2009,113:4413-4418.
[112] Y. J. Sun, Y. Chen, L. J. Tian, et al. Controlled synthesis and morphologydependent upconversion luminescence of NaYF4: Yb, Er nanocrystals [J].Nanotechnology,2007,18:275609.
[113] H. K. Yang, J. H. Jeong. Synthesis, Crystal Growth, and PhotoluminescenceProperties of YAG: Eu3+Phosphors by High-Energy Ball Milling and Solid-StateReaction [J]. J. Phys. Chem. C,2010,114:226-230.
[114] L. Wang, Y. Li. Controlled Synthesis and Luminescence of LanthanideDoped NaYF4Nanocrystals [J]. Chem. Mater.,2007,19,727-734.
[115] C. X. Li, Z. W. Quan, J. Yang, et al. Highly Uniform and Monodisperseβ-NaYF4: Ln3+(Ln=Eu, Tb, Yb/Er, and Yb/Tm) Hexagonal Microprism Crystals:Hydrothermal Synthesis and Luminescent Properties [J]. Inorg. Chem.,2007,46:6329-6337.
[116] F. He, P. P. Yang, D. Wang, et al. Self-Assembled β-NaGdF4Microcrystals:Hydrothermal Synthesis, Morphology Evolution, and Luminescence Properties [J].Inorg. Chem.,2011,50:4116-4124.
[117] Z. L. Wang, J. H. Hao, Chan H L W. Down-and up-conversionphotoluminescence, cathodoluminescence and paramagnetic properties ofNaGdF4:Yb3+, Er3+submicron disks assembled from primary nanocrystals [J]. J.Mater. Chem.,2010,20:3178-3185.
[118] Y. Wu, C. X. Li, D. M. Yang. Rare earth β-NaGdF4fuorides with multiformmorphologies: Hydrothermal synthesis and luminescent properties [J]. J. ColloidInterf. Sci.,2011,354:429-436.
[119] C. X. Li, Z. W. Quan, P. P. Yang, et al. Shape-Controllable Synthesis andUpconversion Properties of Lutetium Fluoride (Doped with Yb3+/Er3+) Microcrystalsby Hydrothermal Process [J]. J. Phys. Chem. C,2008,112,13395-13404.
[120] G. S. Yi, H. C. Lu, S. Y. Zhao, et al. Synthesis, Characterization, andBiological Application of Size-Controlled Nanocrystalline NaYF4:Yb, ErInfrared-to-Visible Up-Conversion Phosphors [J]. Nano Lett.,2004,4,2191-2196.
[121] C. Huang. Coordination Chemistry of Rare Earth Elements, SciencePublishing Press: Beijing,1997.
[122] R. A. Laudise, A. A. Ballman. Hydrothermal Synthesis Of Zinc Oxide AndZinc Sulfide [J]. J. Phys. Chem.,1960,64,688-691.
[123] W. J. Li, E. W. Shi, T. Fukuda. Particle size of powders under hydrothermalconditions [J]. Cryst. Res. Technol.,2003,38,847-858.
[124] G. Y. Chen, G. Somesfalean, Z. G. Zhang, et al. Ultraviolet upconversionfuorescence in rare-earth-ion-doped Y2O3induced by infrared diode laser excitation[J]. Opt. Lett.,2007,32:87-89.
[125] L. Spanhel, M. A. Anderson. Semiconductor clusters in the sol-gel process:quantized aggregation, gelation, and crystal growth in concentrated zinc oxidecolloids [J]. J. Am. Chem. Soc.,1991,113,2826-2833.
[126] N. K. Giri, S. K. Singh, D. K. Rai, et al. SrAl4O7: Tm3+/Yb3+nanocrystallineblue phosphor: structural, thermal and optical properties [J]. Appl. Phys. B,2010,99:271-277.
[127] G. F. Wang, W. P. Qin, L. L. Wang, et al. Intense ultraviolet upconversionluminescence from hexagonal NaYF4:Yb3+/Tm3+microcrystals [J]. Optics Express,2008,16,11907.
[128] J. Li, J. H. Zhang, Z. D. Hao, et al. Spectroscopic Properties andUpconversion Studies in Ho3+/Yb3+Co-doped Calcium Scandate with Spectrally PureGreen emission [J]. ChemPhysChem,2013,14:4114-4120.
[129] O. Morton. Solar energy: A new day dawning?: Silicon Valley sunrise Nature[J]. Nature,2006,443:19-22.
[130] B. Fan, C. Chlique, O. Merdrignac-Conanec, et al. Near-Infrared QuantumCutting Material Er3+/Yb3+Doped La2O2S with an External Quantum Yield Higherthan100%[J]. J. Phys. Chem. C,2012,116:11652-11657.
[131] T. Trupke, M. A. Green, P. Würfel. Improving solar cell efficiencies bydown-conversion of high-energy photons [J]. J. Appl. Phys.,2002,92:1668-1674.
[132] Y. S. Xu, X. H. Zhang, S. X. Dai, et al. Efficient Near-InfraredDown-Conversion in Pr3+-Yb3+Codoped Glasses and Glass Ceramics ContainingLaF3Nanocrystals [J]. J. Phys. Chem. C,2011,115:13056-13062.
[133] G. Gao, L. Wondraczek. Near-infrared downconversion in Pr3+/Yb3+co-doped boro-aluminosilicate glasses and LaBO3glass ceramics [J]. Opt. Mater.Express,2013,3:633-644.
[134] G. Lakshminarayana, J. R. Qiu. Near-infrared quantum cutting in RE3+/Yb3+(RE=Pr, Tb, and Tm): GeO2–B2O3–ZnO–LaF3glasses via downconversion [J]. J.Alloys Compd.,2009,481:582-589.
[135] G. Gao, L. Wondraczek. Near-infrared down-conversion in Mn2+-Yb3+co-doped Zn2GeO4[J]. J. Mater. Chem. C,2013,1:1952-1958.
[136] H. Lin, D. Chen, Y. Yu, et al. Broadband UV excitable near-infrareddownconversion luminescence in Eu2+/Yb3+: CaF2nanocrystals embedded glassceramics [J]. J. Alloys Compd.,2011,509:3363-3366.
[137] X. F. Liu, Y. B. Qiao, G. P. Dong, et al. Cooperative downconversion in Yb3+-RE3+(RE=Tm or Pr) codoped lanthanum borogermanate glasses [J]. Opt. Lett.,2008,33:2858-2860.
[138] C. K. J rgensen. Electron Transfer Spectra [M] Prog. Inorg. Chem.,1970,12:101-158.
[139] A. Bensalah, Y. Guyot, A. Brenier, et al. Spectroscopic properties of Yb3+:LuLiF4crystal grown by the Czochralski method for laser applications and evaluationof quenching processes: a comparison with Yb3+: YLiF4[J]. J. Alloys Compd.,2004,380:15-26.
[140] W. Zheng, H. M. Zhu, R. F. Li, et al. Visible-to-infrared quantum cutting byphonon-assisted energy transfer in YPO4:Tm3+,Yb3+phosphors [J]. Phys. Chem.Chem. Phys.,2012,14:6974-6980.
[141] D. C. Yu, S. Ye, M. Y. Peng, et al. Sequential three-step three-photonnear-infrared quantum splitting in β-NaYF4:Tm3+[J]. Appl. Phys. Lett.,2012,100:191911.
[142] D. C. Yu, X. Y. Huang, S. Ye, et al. A sequential two-step near-infraredquantum splitting in Ho3+singly doped NaYF4[J]. AIP Advances,2011,1:042161.