ErP5O14非晶中Er^3＋离子光谱参数的计数

由测量的ErP_5O_(14)非晶的吸收光谱,计算了Er~(3+)在五磷酸盐非晶中的强度参数Ω_λ,并由此计算了激光能级的振子强度、自发辐射跃迁速率、荧光分支比和积分发射截面。     

Sc_2(WO_4)_3∶Er~(3+)/Yb~(3+)的上转换发光及其温度传感特性

通过高温固相法制备出一系列新型上转换材料Sc_2(WO_4)_3∶Er~(3+)/Yb~(3+)。在980 nm激光激发下,Sc_2(WO_4)_3∶Er~(3+)/Yb~(3+)样品发出肉眼可见的强绿光。利用荧光光度计测得样品的发光光谱,在500～600 nm之间有强绿光发射,分别归因于Er~(3+)的~2H_(11/2)→~4I_(15/2)和~4S_(3/2)→~4I_(15/2)跃迁发射。在650～700 nm位置处,有对应于Er~(3+)离子~4F_(9/2)→~4I_(15/2)跃迁的较弱的红光发射。随着掺杂浓度的变化,样品的红绿分支比发生变化。当样品掺杂Er~(3+)浓度为0.05%、Yb~(3+)浓度等于0.1%时,样品发射的绿光强度是红光强度的27倍。另外,利用荧光强度比方法研究了Er~(3+)的两个热耦合能级在303～573 K范围内的发光温度特性。393 K时,样品的灵敏度达到最大为0.006 8 K~(-1)。对比于其他荧光粉材料,Sc_2(WO_4)_3∶Er~(3+)/Yb~(3+)的灵敏度处于较高水平,在实际测温中具有更好的应用前景。     

高灵敏度下转换光学测温材料:NaGd(WO_4)_2:Yb~(3+)/Er~(3+)

基于Er~(3+)的两个热耦合能级发光强度测量的荧光强度比测温技术由于不受光谱损失和激发强度波动的影响,故能够提供准确的非接触式温度测量。但目前通用的荧光强度比技术都是基于上转换激发,而上转换材料效率较低,测温不准确。考虑到Er~(3+)能级可通过不同激发源来布居,本文利用高能光子激发的高效下转换光学测温方法,来解决上转换发光带来的问题,并以具有高测温灵敏度的钨酸盐NaGd(WO_4)_2为基质。研究发现,NaGd(WO_4)_2可成功用于下转换测温,Yb~(3+)/Er~(3+)共掺样品比Er~(3+)单掺拥有更高的测温灵敏度,且下转换测温灵敏度要高于上转换,在掺杂浓度为20%Yb~(3+)/1%Er~(3+)时,测温灵敏度高达344. 6×10~(-4)K~(-1)。这证明了NaGd(WO_4)_2:Yb~(3+)/Er~(3+)是理想的测温材料,也很好地验证了其在高灵敏度下转换测温的可行性,为荧光强度比技术的应用开辟了新的前景。     

NaY(MoO_4)_2∶Er~(3+)纳米晶体荧光粉的发光与光学温度传感特性(英文)

采用熔盐法制备了不同煅烧温度的NaY(MoO_4)_2∶Er~(3+)荧光粉材料,样品的晶体结构与微观形貌由X射线衍射仪和场发射扫描电镜测得。Er~(3+)掺杂的Na Y(MoO_4)_2纳米晶体的斯托克斯荧光发射光谱是在不同煅烧温度下测得的。NaY(MoO_4)_2∶Er~(3+)荧光粉材料的两个能级~2H_(11/2)-~4I_(15/2)和~4S_(3/2)-~4I_(15/2)跃迁的发射强度比随煅烧温度的增加而减小。NaY(MoO_4)_2∶Er~(3+)荧光粉材料的温度传感特性依赖于Er~3的两个热耦合能级~2H_(11/2)-~4I_(15/2)和~4S_(3/2)-~4I_(15/2)的发射强度。研究表明,在一个相对大的传感温度范围(303~573 K),600℃煅烧的样品的温度传感灵敏度比900℃煅烧的样品高,样品的温度传感灵敏度随煅烧温度的增加而减小,600℃煅烧的样品的温度传感灵敏度为1.36×10~(-2)K~(-1),比900℃煅烧的样品高76.6%。最后,解释了基于不同煅烧温度的温度传感灵敏度的物理机制。     

YNbO_4粉末材料中Er~(3+)发光研究及其光谱性质J-O计算

为了研究Er~(3+)/Yb~(3+)共掺杂YNb O4粉末材料上转换发光特性,采用J-O理论计算了该材料的光谱性质。根据吸收谱各吸收峰面积拟合出谱线强度参数,并根据谱线强度参数计算出理论振子强度和实验振子强度,得到两者均方差为δrms=3.916×10-7。计算了YNb O4粉末材料中Er~(3+)粒子的跃迁几率、跃迁分支比及能级寿命等参数,并计算得到了Er~(3+)离子从能级2H11/2、4S3/2和4F9/2到基态辐射跃迁的受激发射截面。研究结果表明YNb O4材料是一种优良的上转换基质材料。     

LnP_5O_(14)晶体中Tb~(3+)和Eu~(3+)的发光光谱特性

本工作测量了室温下TbP_3O_(14)和EuP_5O_(14)晶体的吸收和发射光谱。根据吸收光谱和Judd-Ofelt理论计算了Tb~(3+)和Eu~(3+)的实验和理论的振子强度。用最小二乘法拟合实验与理论的振子强度得到唯象强度参量Ω_λ。然后计算了Tb~(3+)的~5D_3→~7F_5,~5D_4→~7F_4和~5D_4→~7F_6以及Eu~(3+)的~5D_0→~7F_2,~5D_0→~7F_4的跃迁几率和寿命。同时用时间分辨光谱测量了不同温度下相应的荧光辐射寿命。计算与实验结果基本相符。理论和实验的结果表明Tb~(3+)的~5D_3态的寿命主要取决于~5D_3→~5D_4和~7F_6→~7F_0两能级对之间的电偶极-电偶极交叉弛豫。     

DyP_5O_(14)晶体的光谱强度参数

本文根据Judd-Ofelt理论,利用吸收光谱,计算了DyP_5O_(14)晶体中Dy~(3 )的三个唯象强度参数Ω_λ(λ=2,4,6),求得了计算和实验振子强度,进而计算了约化矩阵元和荧光辐射跃迁几率。     

Er~(3+)和Eu~(3+)共注入GaN的光学特性和能量传递机制

采用离子注入法在GaN薄膜中实现了Er~(3+)和Eu~(3+)离子的共掺杂.以阴极荧光光谱仪为主要表征手段,研究样品的光学特性和能量传递机理.在300K温度下,Er~(3+)和Eu~(3+)共掺杂GaN薄膜能够实现绿光和红光的同时发射.随着Er~(3+)离子掺杂剂量的增加,Eu~(3+)离子相关发光峰的强度减弱,Er~(3+)离子对应的两个相关发光峰强度比值减小,表明Er~(3+)和Eu~(3+)离子之间发生了能量传递,能量传递的方向为Eu~(3+)→Er~(3+).变温阴极荧光光谱显示,Er~(3+)离子的2H11/2和4S3/2两个能态相关的跃迁峰相对强度比值随着温度升高而降低,主要是由两个能级之间的热耦合导致.改变Er~(3+)离子的掺杂剂量,能够调控GaN:Er~(3+)/Eu~(3+)样品的光学色度坐标和色温,表明此材料可用于发光器件.     

磁控溅射制备Er~(3+)/Yb~(3+)共掺杂TiO_2薄膜的上转换发光特性

采用射频磁控溅射法制备得到Er~(3+)/Yb~(3+)TiO_2薄膜,980 nm的抽运源作用下上转换可以得到490 nm的绿光和670 nm的红光,上转换红、绿光发光强度受到烧绿石Er_xYb_(2-x)Ti_2O_7晶体的生成以及Er~(3+)/Yb~(3+)掺杂浓度的影响,实验表明,适量共掺杂Er~(3+)/Yb~(3+)可明显增强上转换发光,Er~(3+)在上转换发光中起主要作用,而引入敏化离子Yb~(3+)可以大大提高上转换发光效率,磁控溅射法制备的TiO_2薄膜声子态密度较小,从而抑制了无辐射跃迁过程,导致490nm绿光形成以及红光强度大于绿光强度。     

构建垂直金纳米棒阵列增强NaYF_4:Yb~(3+)/Er~(3+)纳米晶体的上转换发光

以金纳米棒垂直阵列(gold-nanorods vertical array, GVA)为衬底, SiO_2为隔离层,构建GVA@SiO_2@NaYF_4:Yb~(3+)/Er~(3+)纳米复合结构.在近红外980 nm激发下,通过改变中间隔离层SiO_2的厚度,研究GVA对NaYF_4:Yb~(3+)/Er~(3+)纳米晶体上转换发光的调控规律.实验结果表明,当SiO_2层的厚度增大至8 nm时, Er~(3+)离子整体的上转换发射强度增大近8.8倍,且红光强度增强尤为明显,约为16.2倍.为了进一步证实GVA对Er~(3+)离子红光发射的增强效果,以红光发射为主的NaYF_4:40%Yb~(3+)/2%Er~(3+)纳米晶体为对象展开研究,发现Er~(3+)离子红绿比由1.84增加到2.08,证实该复合结构更有利于提高红光的发射强度.通过对其光谱特性、发光动力学过程的研究并结合其理论模拟,证实了上转换发光的增强是由激发与发射增强共同作用,而激发增强占据主导地位.采用该套复合体结构实现上转换荧光发射的增强,不仅有效地利用了贵金属的等离激元共振特性,而且对深入理解等离激元增强上转换发光的物理机理提供理论依据.     

硼酸铝钕[NdAl3（BO3）4]晶体的晶场能级与发光特性

本文利用晶场理论分析了NdAl_3(BO_3)晶体的光谱特性和相应的能级结构。计算出该晶体的晶场参数,并由此得到了在晶场作用下4~F_(3/2),4~I_(11/2)和4~I_(9/2)三个谱项的所有斯塔克(Stark)子能级的本征波函数。利用所得的波函数和荧光分支比的实验值,用Judd-Ofelt理论估算了4~F_(3/2)→4~I_(11/2)的子能级间跃迁几率的相对值,并讨论了相应的偏振特性,较好地说明了激光和荧光实验的结果。     

Na5Er(WO4)4晶体的光谱参数

Na5Er(WO4)4是化学计量的基质发光晶体,含有很高浓度的Er,它的发光却没有明显的浓度猝灭.与Na5Er(WO4)4结构相同的Na5Nd(WO4)4单晶是良好的激光材料,已获得激光输出.而Er3+在YAlO3,Y3Al5O12和CaF2中也实现了激光输出[1],在ErP5O14[1],Y3Al5O12:Er3+[2]和掺Er3+磷酸盐玻璃[3]的光学参数和某些谱线出激光的可能性已有研究.     

Crystal field and exchange interactions in the SmFe3(BO3)4 multiferroic

The optical spectra of oriented SmFe₃(BO₃)₄ single crystals are studied in the region of the f-f transitions in the Sm³⁺ ion by Fourier spectroscopy. The energies, the symmetry properties, and the exchange splittings of the Stark sublevels of the ground and 17 excited multiplets of the Sm³⁺ ion in a crystal field of symmetry D ₃ are determined from the measured temperature dependences of polarized-radiation absorption spectra. The parameters of the crystal field acting on samarium ions and the parameters of the exchange interaction between Sm³⁺ and Fe³⁺ ions are found. The anisotropy of the effective exchange interaction is shown to be substantially stronger than the magnetic anisotropy, due to a strong crystal-field-induced mixing of the ground and excited multiplets.     

Spectroscope studies of YAlO_3: (Lu~(3 )Nd~(3 ))

An increase of the Nd~(3 ) doping concentration and an enhancement of the laser induced fluorescence in the single crystal of YAlO_3: (Lu~(3 ), Nd~(3 )) have been observed and are attributed to the size compensation effect. The low temperature (4.2K) fluorescence spectra indicate that the structure of the sharp lines arising from the radiative transitions of Nd~(3 ) ions is not changed by the existence of Lu~(3 ) ions, but the emission lines are inhomogeneously more broadened. Besides, it has been observed that the fluorescence due to the radiative transition from the Stark's sublevel R_2 of the metastable level ~4F_(3/2) to the sublevels Y_1 of the manifold ~4I_(11/2) decreases with decreasing temperature and the fluorescence arising from the transitions R_1→Y_1 is relatively increased. The experimental fact is qualitatively interpreted.     

Crystal field splittings and luminescence properties for Nd3+, Er3+ and Dy3+ in yttrium orthoaluminate (YAlO3)

This report contains information appropriate for a theoretical analysis of the optical spectra of triply ionized lanthanides in YAlO₃. Starting with the best-fit crystal field parameters, the crystal field splitting schemes, multiplet-to-multiplet line strengths, radiative lifetimes, branching ratios, line-to-line square matrix elements and g-factors for the triply ionized Nd, Er and Dy in YAlO₃ have been calculated. In this paper detailed discussions were made on the luminescence properties of the principal transitions of Nd-doped YAlO₃ emanating from the metastable ⁴F_{$\text{3}\text{2}$} state to Stark components of multiplets of the ground ⁴I_J term and compared to similar results of Y₃Al₅O₁₂ (YAG). The line-to-line branching ratios were calculated including J-mixing effects. In the calculations, only electric dipole transitions were considered because of odd-parity. The results predicted some interesting differences in the optical behavior of Nd³⁺ in these two host materials. It has been observed that there is a reasonable agreement between the theoretical data and those reported experimentally for YAlO₃ and YAG. The theoretical studies undertaken here were chosen to supplement or extend the optical data for these two host materials.     

Intensities of inter-Stark transitions in YAG-Yb3+ crystals

The line strengths of indirect electric dipole and magnetic dipole transitions between Stark sublevels of the Yb³⁺ impurity ion in a YAG crystal are calculated. The intensity’s parameters are determined, and the spectroscopic characteristics of inter-Stark transitions (probabilities of spontaneous transitions and radiative lifetimes of Stark sublevels of excited multiplet, fluorescence branching ratios, transition cross sections, and absorption coefficients) are computed. Quantitative calculations of spectroscopic parameters revealed a quite reasonable agreement with experimental data.     

Phase transitions in KIO(3)

The high-pressure behavior of KIO(3) was studied up to 30?GPa using single crystal and powder x-ray diffraction, Raman spectroscopy, second harmonic generation (SHG) experiments and density functional theory (DFT)-based calculations. Triclinic KIO(3) shows two pressure-induced structural phase transitions at 7?GPa and at 14?GPa. Single crystal x-ray diffraction at 8.7(1)?GPa was employed to solve the structure of the first high-pressure phase (space group R3, a?=?5.89(1) ?, α?=?62.4(1)°). The bulk modulus, B, of this phase was obtained by fitting a second order Birch-Murnaghan equation of state (eos) to synchrotron x-ray powder diffraction data resulting in B(exp,second)?=?67(3)?GPa. The DFT model gave B(DFT,second)?=?70.9?GPa, and, for a third order Birch-Murnaghan eos, B(DFT,third)?=?67.9?GPa with a pressure derivative of [Formula: see text]. Both high-pressure transformations were detectable by Raman spectroscopy and the observation of second harmonic signals. The presence of strong SHG signals shows that all high-pressure phases are acentric. By using different pressure media, we showed that the transition pressures are very strongly influenced by shear stresses. Earlier work on low- and high-temperature transitions was complemented by low-temperature heat capacity measurements. We found no evidence for the presence of an orientational glass, in contrast to earlier dielectric studies, but consistent with earlier low-temperature diffraction studies.     

Correlation between the intensities of intermultiplet electric dipole transitions and the fine features of the stark structure of multiplets of Pr3+ ions in the LaCl3 compound

The Stark structure of the multiplets of Pr³⁺ ions in the LaCl₃ compound is described and the even and odd parameters of the crystal field, as well as the covalency parameters, are determined in the approximation of an intermediate interconfiguration interaction. The covalency parameters thus obtained agree well with the parameters calculated in the framework of microscopic models. The intensity parameters of intermultiplet electric dipole transitions are calculated using the odd parameters of the crystal field and the covalency parameters. The results of the calculations are in satisfactory agreement with the experimental data. This allows the conclusion that there is a correlation between the fine features of the Stark structure of the multiplets and the intensities of the intermultiplet electric dipole transitions.     

Electronic absorption spectra of the 5d3 hexafluororhenate(IV) ion

The Γ₈(⁴A_2g) →Γ₇(²T_2g), Γ₈(²T_2g) electronic transitions for the 5d³ hexafluororhenate(IV) ion have been observed at liquid hydrogen temperature in a single Cs₂GeF₆ crystal and in a mixed crystal where the ReF^?2₆ ion is doped in the cubic Cs₂GeF₆ lattice. The electronic transitions have been assigned with a crystal field model to give information about the parameters B, C, Dq, and spin-orbit coupling. The vibrational structure in the mixed crystal system may be assigned to the ungerade modes of the ReF^?2₆ moiety. Comparison of the mixed and pure crystal vibrational structure shows that the pure crystal vibrational structure can be interpreted on the basis of K ≠ 0 lattice effects and a small distortion in the pure crystal.     

X-ray studies of the (La,Sr)MnO<Subscript>3</Subscript> perovskite manganite structure

X-ray studies of perovskite manganites (La_0.9Sr_0.1)_0.9MnO₃ and La_1?xSr_xMnO₃ (x = 0.1, 0.15, 0.2, 0.25) are reported. The atom positions and interatomic distances and angles are calculated as a function of Sr doping at room temperature using the FullProf software. The temperature dependences of the crystal lattice parameters and unit cell volume are investigated. The effects of structural and magnetic phase transitions on the crystal lattice parameters are studied in detail. The bulk magnetoelastic contribution to thermal expansion is studied experimentally and calculated.