Tm3+/Yb3+共掺碲酸盐玻璃的近红外发光及能量传递机理

采用高温熔融法制备了组分为TeO2-ZnO-Na2O的Tm3+离子单掺和Tm3+/Yb3+共掺碲酸盐玻璃,应用Judd-Ofelt理论计算分析了玻璃样品的强度参量Ωt(t=2,4,6),自发辐射跃迁几率A,荧光分支比β和荧光辐射寿命τrad等光谱参量,测量得到了不同Yb3+离子掺杂浓度下玻璃样品的Tm3+离子上转换发光谱.结果显示,在980nm泵浦光激励下玻璃样品发射出强烈的近红外上转换荧光.对Tm3+离子上转换发光分析表明,强烈的Tm3+离子近红外上转换发光主要来自于Yb3+/Yb3+离子间的共振能量传递以及基于单声子和双声子辅助的Yb3+/Tm3+离子间的非共振能量传递过程,并进一步计算得到了声子贡献比和能量传递系数.最后,计算分析了Tm3+∶3 F4→3 H6能级间跃迁的1.8μm波段吸收截面、受激发射截面和增益系数.研究表明,Yb3+/Tm3+共掺TeO2-ZnO-Na2O玻璃可以作为近红外波段固体激光器的潜在增益基质.     

High-power diode-cladding-pumped Tm<Superscript>3+</Superscript>, Ho<Superscript>3+</Superscript>-doped silica fibre laser

The fundamental characteristics of a continuous-wave high-power diode-pumped Tm³⁺, Ho³⁺-doped double-clad silica fibre laser are presented. A maximum output power of 5.2 W was measured and was generated at a slope efficiency of 42 (44)% with respect to the launched (absorbed) pump power. At the optimum length of 7 m (_effL=2.9, where _eff is the effective absorption coefficient of the fibre and L is the fibre length), the fibre laser output was measured to have a centre wavelength of 2105 nm and a line width of 20 nm. The centre wavelength of the emission was tunable over a 32-nm extent when 0.68<_effL<3.28 or for a 6.2-m change in L. PACS 42.55.Wd; 42.55.Xi; 42.60.Lh; 42.60.Pk     

Tm3+/Ho3+掺杂碲酸盐玻璃的上转换发光性能与能量转换机制

采用高温熔融法制备了单掺Tm3+和Tm3+/Ho3+共掺碲酸盐玻璃,测试了808 nm激光泵浦下玻璃的红外和上转换荧光光谱。Tm3+/Ho3+共掺碲酸盐玻璃上转换荧光光谱主要由695 nm红光、544 nm绿光、474 nm蓝光和740 nm红光四个发光带组成。通过分析样品的光谱性能和能量转换机制,发现很少报道的740 nm红光可能是由Tm3+：1D₂ →3F_{2, 3}能级跃迁产生的。在掺杂0.5 mol％ Tm₂O₃的样品中添加0.3 mol％ Ho₂O₃,695 nm红光、740 nm红光和474 nm蓝光等上转换发光强度明显增大,大约分别是单掺0.5 mol％ Tm₂O₃样品中发光强度的3倍,2.5倍和14倍。这些情况说明存在着强烈的Ho3+→Tm3+反向能量传递。单掺Tm3+碲酸盐玻璃中1D₂能级(发射740 nm红光)上的粒子集居主要来源于合作上转换(CU)过程,而3F_{2, 3}能级(发射695 nm红光)上的粒子集居除了来源于CU过程之外,还有740 nm红光的发射和1G₄能级上部分粒子的无辐射跃迁(1G₄→3F_{2, 3})两条途径,因此样品中695 nm红光强度明显要大于740 nm红光强度。通过交叉驰豫作用CR2和CR3以及反向共振能量转移RET2,Tm3+/Ho3+共掺碲酸盐玻璃中Tm3+的1G₄能级(发射474 nm蓝光)上的粒子集居数比单掺Tm3+时出现了净增加。Tm3+的1G₄能级上粒子集居数的增加可能进一步强化了该能级的无辐射跃迁、740 nm红光的发射以及CU过程,并进而促使Tm3+的3F_{2, 3}能级上的粒子集居。所以,当Tm3+/Ho3+共掺碲酸盐玻璃与单掺Tm3+碲酸盐玻璃中掺杂相同浓度的Tm3+时,前者的红光和蓝光等上转换荧光强度均比后者要大。本文还研究了Tm3+之间以及Tm3+与 Ho3+之间的交叉弛豫和能量传递等效应,并进一步探讨了Tm3+与 Ho3+之间的能量转换机制。     

铒离子浓度对掺Er3+碲酸盐玻璃的Judd-Ofelt理论参数的影响

制备了四种不同铒离子掺杂浓度的碲酸盐玻璃,通过测定吸收光谱计算了吸收谱线的振子强度,根据Judd-Ofelt理论计算了不同浓度下Er3 离子发光光谱的强度参数Ωi(i=2,4,6),计算了自发辐射电偶和磁偶跃迁概率、辐射寿命、荧光分支比等参数,讨论了Er3 离子浓度变化对以上这些参数的影响.测试了Er3 :4I13/2→4I15/2跃迁对应的荧光光谱和Er3 :4I13/2能级荧光寿命.最后应用McCumber理论计算了玻璃中Er3 :4I13/2→415/2跃迁对应的受激发射截面大小.结果表明:振子强度基本上随Er3 离子浓度的增大而增强;随着Er3 离子浓度的增加,自发辐射跃迁概率A基本呈现出递增的趋势,但荧光分支比β却只有很小的变化;Er3 :4I13/2→4I15/2的发射截面随Er3 离子浓度的增大而改变很小,有效线宽都在50 nm左右.     

Tm3+/Yb3+共掺碲酸盐玻璃的近红外发光及能量传递机理

采用高温熔融法制备了组分为TeO₂-ZnO-Na₂O的Tm³⁺离子单掺和Tm³⁺/Yb³⁺共掺碲酸盐玻璃,应用Judd-Ofelt理论计算分析了玻璃样品的强度参量Ω_t(t=2, 4, 6),自发辐射跃迁几率A,荧光分支比β和荧光辐射寿命τ_rad等光谱参量,测量得到了不同Yb³⁺离子掺杂浓度下玻璃样品的Tm³⁺离子上转换发光谱.结果显示,在980 nm泵浦光激励下玻璃样品发射出强烈的近红外上转换荧光.对Tm³⁺离子上转换发光分析表明,强烈的Tm³⁺离子近红外上转换发光主要来自于Yb³⁺/Yb³⁺离子间的共振能量传递以及基于单声子和双声子辅助的Yb³⁺/Tm³⁺离子间的非共振能量传递过程,并进一步计算得到了声子贡献比和能量传递系数.最后,计算分析了Tm³⁺:³F₄→³H₆能级间跃迁的1.8 μm波段吸收截面、受激发射截面和增益系数.研究表明,Yb³⁺/Tm³⁺共掺TeO₂-ZnO-Na₂O玻璃可以作为近红外波段固体激光器的潜在增益基质.     

掺饵碲酸盐玻璃的光谱性质和能量传递

测试了掺Er碲酸盐玻璃在974nmLD泵浦下的吸收光谱、荧光光谱和上转换光谱，应用McCumber理论计算了Er^3 的受激发射截面，分析了碲酸盐玻璃中Er^3 离子的上转换发 光机制，研究了Yb^3 离子对Er^3 离子上转换发光强度的影响以及两者之间的能量传递特性。     

The comparative analysis and optimization of the free-running Tm<Superscript>3+</Superscript>:YAP and Tm<Superscript>3+</Superscript>:YAG microlasers

The thulium microlasers based on yttrium-aluminium perovskite and yttrium-aluminium garnet crystals are considered as coherent light sources at the wavelength near 2 μm. The comparative analysis of these lasers is carried out by means of the lasers’ parameters optimization for each value of the pumping power taking into consideration the cross-relaxation and up-conversion processes as well as heating of the active medium. The optimal values of the active medium length, activator concentration and the output mirror reflectivity are determined both for Tm:YAP- and Tm:YAG-laser. The pulse generation of Tm:YAP- and Tm:YAG-lasers is also considered, the parameters of this regime are determined. The comparison shows the suitability of Tm:YAP laser crystal both for cw and pulse generation. The up-conversion influence on the laser characteristics is also analyzed. PACS 42.60.Gd     

793 nm抽运下的掺Tm3+碲酸盐玻璃的发光特性

研究了掺Tm^3 碲酸盐玻璃在793nm钛宝石激光器抽运下的发光特性，结果发现除常规的^3H4→^3H6的811nm荧光外，还存在很强的^1G4→H5的785nm二光子转换荧光以及较弱的710nm和677nm三光子上转换荧光。     

Stable and Efficient Pulsed Mid-Infrared Laser Generation from an Er<Superscript>3+</Superscript>-Doped ZBLAN Fiber Laser

We demonstrate a stable and efficient passively Q-switched 2.8 μm Er³⁺-doped ZBLAN fiber laser with a broadband semiconductor saturable absorber mirror. Enabled by the broadband optical modulator, the stable Q-switched fiber laser can deliver a maximum average power over 700 mW with corresponding per-pulse energy of 8.19 μJ and a pulse width of 1.3 μs at a repetition rate of 88.6 kHz under an incident pump power of 3.8 W. In addition, the slope efficiency can reach 22.5%. To the best of our knowledge, this is the highest reported slope efficiency for the passively Q-switched Er³⁺-doped ZBLAN fiber laser.     

Enhanced Up-Conversion Emission in Al<Superscript>3+</Superscript> Co-Doped ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript>:Yb<Superscript>3+</Superscript>,Tm<Superscript>3+</Superscript> Powder Phosphors

Yb³⁺-Tm³⁺ co-doped up-conversion powder phosphors using Zn(Al_xGa_1-x)₂O₄ (ZAGO) as the host materials were synthesized via solid-state reaction successfully. In addition, the morphology, structural characterization and up-conversion luminescent properties were all investigated by scanning electron microscope (SEM), x-ray diffraction (XRD) and fluorescence spectrophotometer (F-7000), respectively. Under the excitation of a 980 nm laser, all as-prepared powders can carry out blue emission at about 477 nm (corresponding to ¹G₄ → ³H₆ transition of Tm³⁺ ions), and red emission at about 691 nm (attributed to ³F₃ → ³H₆ transition of Tm³⁺ ions). Also, the influence of doping Al³⁺ ions were investigated. In brief, the doping of Al³⁺ ions has no effect on the position of emission peak. Howbeit the up-conversion efficiency and intensity of ZAGO:Yb,Tm phosphors are stronger than ZGO:Yb,Tm and ZAO:Yb,Tm phosphors, while the crystallinity is the opposite. More particularly, all as-prepared powder phosphors emit strong luminescence, which is observable by the naked eye, demonstrating the potential applications in luminous paint, luminescent dye, etc.     

Dy~(3+)-Tb~(3+)掺杂氟氧碲酸盐玻璃的光谱性能研究

实验采用高温熔融法制备了一系列Dy3+离子、Tb3+离子单掺或共掺氟氧碲酸盐玻璃样品.测试了不同摩尔含量的Dy3+离子和Tb3+离子的氟氧碲酸盐玻璃样品的密度,分析了紫外-可见透射光谱、激发光谱、发射光谱、发光衰减曲线,研究了不同摩尔含量的Dy3+离子和Tb3+离子的氟氧碲酸盐玻璃样品光谱性能及Dy3+离子到Tb3+离子能量传递机理.结果表明:Dy3+离子、Tb3+离子单掺或共掺氟氧碲酸盐玻璃样品的密度均大于5g·cm-3,最大可达6.09g·cm-3;Dy3+离子可以敏化Tb3+离子,促进其发光,但当Dy3+离子超过一定浓度后,会发生离子间浓度猝灭效应,Tb3+离子的发光反而降低.试验测得,Dy3+离子的最佳掺杂浓度为1.0mol%,此时,Tb3+离子掺杂浓度为6.0mol%,Tb3+离子发光效果最强.依据Dexter能量传输理论,并对Dy3+离子和Tb3+离子的能级图及能级间的跃迁进行分析,可知Dy3+离子和Tb3+离子间的能量传递方式为非辐射共振传递.     

Green,blue, red,near-infrared up-conversion luminescence of Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>/Tm<Superscript>3+</Superscript> co-doped YVO<Subscript>4</Subscript> nanoparticles

YVO₄:Yb³⁺,Er³⁺; YVO₄:Yb³⁺,Tm³⁺; and YVO₄:Yb³⁺,Er³⁺,Tm³⁺ were all synthesized via sol-gel method with a subsequent thermal treatment. Specifically, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ phosphors were prepared with different annealing temperatures to study the influence of temperature. The transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffractometer (XRD), and photoluminescent (PL) spectrofluorometer were used to investigate the morphology, crystal structure, and up-conversion luminescent properties of all samples. In summary, all samples were granular-like nanoparticles and well crystallized with the same tetragonal phase as YVO₄. Under the irradiation at 980 nm, YVO₄:Yb³⁺,Er³⁺ phosphors can generate green emission at 525 and 553 nm and red emission at 657 nm, while YVO₄:Yb³⁺,Tm³⁺ phosphors can generate blue emission at 476 nm, red emission at 648 nm, and near-infrared emission at 800 nm. Notably, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ samples can exhibit green emission, blue emission, red emission, and near-infrared emission at the same time, which might endow the as-prepared samples with potential applications in many fields, such as luminous paint, infrared detection, and biological label.     

Spectroscopic Properties and Energy Transfer Analysis of Tm<Superscript>3+</Superscript>-Doped BaF<Subscript>2</Subscript>-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript>-La<Subscript>2</Subscript>O<Subscript>3</Subscript> Glass

This paper reports on the spectroscopic properties and energy transfer analysis of Tm³⁺-doped BaF₂-Ga₂O₃-GeO₂-La₂O₃ glasses with different Tm₂O₃ doping concentrations (0.2, 0.5, 2.0, 2.5, 3.0, 3.5, 3.5, 4.0 wt%). Mid-IR fluorescence intensities in the range of 1,300 nm−2,200 nm have been measured when excited under an 808 nm LD for all the samples with the same pump power. Energy level structure and Judd-Ofelt parameters have been calculated based on the absorption spectra of Tm³⁺, cross-relaxation rates and multi-phonon relaxation rates have been estimated with different Tm₂O₃ doping concentrations. The maximum fluorescence intensity at around 1.8 μm has been obtained in Tm₂O₃-3 wt% sample and the maximum value of calculated stimulated emission cross-section of Tm³⁺ in this sample is about 0.48 × 10⁻²⁰ cm² at 1,793 nm, and there is not any crystallization peak in the DSC curve of this sample, which indicate the potential utility of Tm³⁺-doped BaF₂-Ga₂O₃-GeO₂- La₂O₃ glass for 2.0-μm optical fiber laser.     

Observation and interpretation of the Tm<Superscript> 3+</Superscript> free ion spectrum

The emission spectrum of thulium produced by a vacuum spark source was observed in the wavelength range from 700 to 2320 ? on the 10.7 m normal-incidence vacuum ultraviolet spectrograph at the Paris-Meudon observatory. In the unknown spectrum of Tm IV, more than 760 lines have been identified for the first time as transitions between 157 levels of 4f¹¹5d, 33 levels of 4f¹¹6p, 9 levels of 4f¹¹6s and 10 levels of the 4f¹² ground configuration. A parametric interpretation of the levels has been carried out using the Cowan codes. Configuration interaction effects are discussed, in particular with the core-excited configurations 5p⁵4f¹³ and 5p⁵4f¹²5d. Radial Slater parameters derived from 4f¹² levels are larger than those pertaining to trivalent Tm ions in compounds. A selection of 105 prominent lines is given.     

Spectroscopic indications of the possible optical cooling effect in fluoride crystals activated by Yb<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

The results of spectral kinetic studies of several fluoride crystals activated by Yb³⁺ and Tm³⁺ ions are presented, and their possible application as cooling elements of optical refrigerators is discussed. Optimum excitation conditions for the laser cooling effect in these crystals are found. The cooling efficiency is established to depend on the degree of order in the active medium.     

The upconversion luminescence and magnetism in Yb<Superscript>3+</Superscript>/Ho<Superscript>3+</Superscript> co-doped LaF<Subscript>3</Subscript> nanocrystals for potential bimodal imaging

Biocompatible upconversion nanoparticles with multifunctional properties can serve as potential nanoprobes for multimodal imaging. Herein, we report an upconversion nanocrystal based on lanthanum fluoride which is developed to address the imaging modalities, upconversion luminescence imaging and magnetic resonance imaging (MRI). Lanthanide ions (Yb³⁺ and Ho³⁺) doped LaF₃ nanocrystals (LaF₃ Yb³⁺/Ho³⁺) are fabricated through a rapid microwave-assisted synthesis. The hexagonal phase LaF₃ nanocrystals exhibit nearly spherical morphology with average diameter of 9.8 nm. The inductively coupled plasma mass spectrometry (ICP-MS) analysis estimated the doping concentration of Yb³⁺ and Ho³⁺ as 3.99 and 0.41%, respectively. The nanocrystals show upconversion luminescence when irradiated with near-infrared (NIR) photons of wavelength 980 nm. The emission spectrum consists of bands centred at 542, 645 and 658 nm. The stronger green emission at 542 nm and the weak red emissions at 645 and 658 nm are assigned to ⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺, respectively. The pump power dependence of luminescence intensity confirmed the two-photon upconversion process. The nanocrystals exhibit paramagnetism due to the presence of lanthanide ion dopant Ho³⁺ and the magnetization is 19.81 emu/g at room temperature. The nanocrystals exhibit a longitudinal relaxivity (r ₁) of 0.12 s^?1 mM^?1 and transverse relaxivity (r ₂) of 28.18 s^?1 mM^?1, which makes the system suitable for developing T2 MRI contrast agents based on holmium. The LaF₃ Yb³⁺/Ho³⁺ nanocrystals are surface modified by PEGylation to improve biocompatibility and enhance further functionalisation. The PEGylated nanocrystals are found to be non-toxic up to 50 μg/mL for 48 h of incubation, which is confirmed by the MTT assay as well as morphological studies in HeLa cells. The upconversion luminescence and magnetism together with biocompatibility enables the adaptability of the present system as a nanoprobe for potential bimodal imaging.     

Er3+/Tm3+共掺碲酸盐玻璃光谱特性及能量传递

采用高温熔融法制备了两系列不同掺杂比的Er³⁺/Tm³⁺共掺的碲酸盐玻璃,测试了样品的吸收光谱和在980 nm LD激发下的发光光谱、上转换发光光谱及发光寿命。讨论了Er³⁺与Tm³⁺掺杂浓度对样品光谱性质的影响,Tm³⁺离子的掺入会减弱Er³⁺的1.53 μm发光强度,但通过共振能量传递可以获得Tm³⁺的1.8 μm发光,并随着Tm³⁺离子浓度的增加而增强。同时表明Tm³⁺离子的增加会减弱Er³⁺离子在528 nm和545 nm附近的上转换绿光强度,而上转换红光出现了先增强后减弱的现象。研究了Er³⁺/Tm³⁺共掺杂碲酸盐玻璃的能量传递机制与传递效率,分析了Tm³⁺/Er³⁺离子掺杂浓度比对上转换发光的影响。     

Molecular self-organization of Ho<Superscript>3+</Superscript> impurity ions in synthetic forsterite

The structure of paramagnetic centers formed by impurity Ho³⁺ ions in synthetic forsterite is studied by submillimeter EPR spectroscopy in the frequency range 65–200 GHz. It is found that Ho³⁺ enters into the Mg²⁺ sublattice in the form of single ions and dimer centers. The concentration of dimer centers considerably exceeds the concentration of single ions, which points to the molecular self-organization of Ho³⁺ impurity ions into dimers during the growing of the crystals from melt. Possible structures of the dimer center are discussed. The parameters of the effective spin Hamiltonian describing the behavior of the electron-nuclear sublevels of the two lowest electronic levels of the Ho³⁺⁵I₈ ground multiplet are determined for a single ion and a dimer center.     

Structural Properties of Cr<Superscript>3+</Superscript>-Doped Cadmium Oxide Nanopowders

The Cr³⁺-doped cadmium oxide nanopowder is prepared at room temperature by a mild and simple solution method. The prepared powder is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical, electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) techniques. The XRD powder pattern reveals the lattice structure and cell parameters are evaluated. The SEM image shows the stone-like morphology of the nanopowder. The optical absorption spectrum indicates the distorted octahedral site symmetry of Cr³⁺ ions. The crystal field Dq and interelectronic repulsion parameters B and C are evaluated. The EPR spectrum gives a resonance signal at g = 1.973 for Cr³⁺ ions. The FT-IR spectrum reveals the characteristic vibrations of cadmium oxide.