球形BaZnF_4∶Yb,Er纳米颗粒的热分解法合成及其上转换发光性质

采用热分解法制备了Ba Zn F4∶Yb,Er纳米颗粒。通过荧光分光光度计、X射线粉末衍射仪(XRD)和透射电子显微镜(TEM)对样品进行了表征。合成样品的形貌为球形,晶相为四方相,平均粒径为8 nm。当敏化剂Yb3+和激活剂Er3+的掺杂摩尔分数分别为20%和4%时,样品的发光性能较好。绿光和红光发射对应的辐射跃迁分别为Er3+离子的2H11/2→4I15/2(绿光)和4S3/2→4I15/2(绿光),以及Er3+离子的4F9/2→4I15/2(红光)。     

Energy Back Transfer Induced Color Controllable Upconversion Emissions in La2MoO6:Er3+/Yb3+ Nanocrystals for Versatile Applications

Color controllable Er³⁺/Yb³⁺‐codoped La₂MoO₆ upconverting nanocrystals are successfully synthesized via a facile sol‐gel method. Under the irradiation of 980 nm light, the entire samples exhibit dazzling upconversion (UC) emissions arising from the intra‐4f transitions of Er³⁺ ions and the UC emission intensity is strongly dependent on the Yb³⁺ ion concentration. Moreover, by controlling the Yb³⁺ ion concentration, the emission color is changed from green to yellow and finally to red as a result of the energy back transfer from Er³⁺ to Yb³⁺ ions, which is further verified by the theoretically discussion based on the steady‐state rate expressions. The optical thermometric properties of the prepared nanocrystals based on the (²H_11/2,⁴S_3/2) thermally coupled levels of Er³⁺ ions are systematically studied by analyzing the temperature‐dependent green UC emission spectra in the range of 303–663 K. The maximum sensor sensitivity of resultant nanocrystals is determined to be 0.0083 K⁻¹ at 510 K. Furthermore, the emitting color of the synthesized nanocrystals relies on the temperature. In addition, the heating effect induced by the excitation pump power is also investigated and the host lattice temperature is enhanced from 319 to 404 K with raising the pump power from 159 to 757 mW.     

超薄金壳包覆NaYF4:Yb,Er@SiO2纳米结构的可控合成与表面增强上转换荧光

利用原位还原法成功制备了尺寸均一、超薄完整金壳包覆的NaYF₄:Yb,Er@SiO₂@Au（NSA）纳米结构,其XRD、TEM、EDX、HRTEM-HAADF、Mapping及吸收光谱表征结果表明,SiO₂壳及纳米金壳的平均厚度分别约为5 nm和2 nm。在980 nm连续激光激发下,系统研究了核壳结构的上转换荧光强度与氯金酸浓度的依赖关系。稳态光谱结果显示,NSA与仅SiO₂包覆样品（NS）相比Er³⁺的红绿荧光强度均增强了~2.8倍。通过分析上转换荧光动力学过程及利用FDTD方法模拟,讨论了表面等离激元增强上转换荧光的机制。     

Upconversion in Detail: Multicolor Emission of Yb/Er/Tm-Doped Nanoparticles under 800, 975, 1208, and 1532 nm Excitation Wavelengths

Spectroscopic properties of YPO₄ nanoparticles doped with Yb³⁺, Tm³⁺, and Er³⁺ ions have been studied in detail. These multiemitting materials are promising not only for photonic or electronic use but especially for anticounterfeiting applications. The nanopowders are synthesized by the facile coprecipitation method with annealing in the air atmosphere at 1000 °C. The structural and morphological studies reveal pure tetragonal nanocrystallites with an average size of 20–30 nm. Most interestingly, under NIR excitation, the samples exhibit intense upconversion (UC) luminescence where the color can be tuned by changing the laser source, switching the excitation wavelengths between 800, 975, 1208, and 1532 nm, double-wavelength excitation, and by changing laser power density. As a result, a very high color shift, being the result of intensity changes in the emission bands of Er³⁺ (green and red) and Tm³⁺ (blue and red) is obtained. The luminescence lifetimes, temporal evolution, and the pump power dependences are also measured to propose the mechanisms responsible for the observed UC emission.     

VUV-UV excited luminescent properties of LnCa4O(BO3)3:RE (Ln=Y, La, Gd; Re=Eu, Tb, Dy, Ce)

Calcium lanthanide oxyborate doped with rare-earth ions LnCa₄O(BO₃)₃:RE³⁺ (LnCOB:RE, Ln=Y, La, Gd, RE=Eu, Tb, Dy, Ce) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos’ and Jφrgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. Jφrgensen, Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band E_ct were calculated and compared with their excitation spectra.Eu³⁺ and Tb³⁺ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce³⁺ ions do not show efficient luminescence and quench the luminescence of Tb³⁺ ions when Tb³⁺ and Ce³⁺ ions are co-doped into LnCOB. GdCOB doped with Dy³⁺ shows yellowish white light under irradiation of 254 nm light for the reason that Gd³⁺ ions transfer the energy from itself to Dy³⁺. Because of the existence of Gd³⁺, the samples of GdCOB:RE³⁺ show higher excitation efficiency than LaCOB:RE³⁺ and YCOB:RE³⁺, around 188 nm, which indicates that the Gd³⁺ ions have an effect on the host absorption and can transfer the excitation energy to the luminescent center such as Tb³⁺, Dy³⁺ and Eu³⁺.     

热解法制备KY3F10: Yb, RE(RE=Er, Ho, Tm)纳米晶及其特性研究

有机染料和量子点等荧光标记材料存在发射光谱宽、 光热稳定性差和细胞毒性等缺陷, 限制了其在生物学研究中的应用. 镧系掺杂上转换发光材料不存在"自发荧光"和"光漂白"现象, 灵敏度高, 长期稳定性好, 利于活体检测. 论文首次采用热解法, 以油酸和十八烯为表面活性剂和溶剂, 制备了KY₃F₁₀: Yb, RE(RE=Er, Ho, Tm) 纳米晶. 研究了油酸含量对产物形貌和粒径尺寸的影响, 当油酸与十八烯的比例为3:1时, 为制备类球形单分散纳米晶体的最佳工艺条件, 在980 nm半导体激光器激发下, 样品KY₃F₁₀: Yb, RE(RE=Er, Ho, Tm) 分别发射出较强的黄绿、 绿色和蓝色光, 这些结果显示KY₃F₁₀: Yb, RE(RE=Er, Ho, Tm) 纳米粒子作为生物探针在多重荧光标记方面具有优异的特性.     

Er,Yb：(LaLu)2O3透明陶瓷制备及上转换发光性能

采用柠檬酸燃烧法制备Er,Yb：（LaLu）₂O₃陶瓷粉体,用X射线衍射对其进行了物相鉴定,研究表明1 000℃时已经得到纯相的（LaLu）₂O₃。采用冷等静压-真空烧结法制备了Er,Yb：（LaLu）₂O₃和Er：（LaLu）₂O₃陶瓷,对陶瓷的结构和光谱性能进行了详细的研究,研究发现掺杂5% Yb³⁺和10% La³⁺样品的上转换发光强度与未掺Yb³⁺、La³⁺样品相比明显增大,根据上转换光谱显示较强发射峰位于564 nm和661 nm处,对应Er³⁺的⁴S_3/2（²H_11/2）→⁴I_15/2能级跃迁和⁴F_9/2→⁴I_15/2能级跃迁,并讨论了Er³⁺-Yb³⁺的能量传递过程及其上转换发光机制。     

The temperature‐sensitive luminescence of (Y,Gd)VO4:Bi3+,Eu3+ and its application for stealth anti‐counterfeiting

Anti‐counterfeiting technologies are desired to protect products far away from the violation of dummy, fake and shoddy goods. The phosphor of (Y,Gd)VO₄:Bi³⁺,Eu³⁺ was synthesized for the application of this purpose. Its photoluminescence was investigated by exciting with different wavelengths at variant temperatures. Wide emission color ranged from green through yellow to orange was tuned up by tailor‐ing Bi³⁺ and Eu³⁺ concentrations. The temperature dependent luminescence and wavelength selective excitation of (Y,Gd)VO₄:Bi³⁺,Eu³⁺ were observed, which provide different encryptions in anti‐counterfeiting. To verify the feasibility in application, two anti‐counterfeiting patterns were fabricated practically and excellent performance was obtained. Moreover, the physical mechanisms for the different phenomena of luminescence were elucidated from excitation spectra combining with the configuration coordinate model. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and scintillating properties of Ce:Li(Y,Lu)F4 single crystals

We have investigated the optical and scintillating properties of Lu co-doped Ce:LiYF₄ single crystals with various Lu content. In the transmittance and absorption spectra, the absorption peaks at 243 nm get systematically red shifted in contrast to the peaks at 197 and 200 nm which get blue shifted with the increase in Lu content. At the same time, emission peaks at 306 nm and 200 nm under 295 nm excitation also get red shifted. The decay time of Ce:Li(Y,Lu)F₄ crystals under 295 nm excitation is found to be faster than that of Ce:LiYF₄ and Ce:LiLuF₄ crystals. The alpha-peak positions in the pulse-height spectra and decay times of crystals under alpha-ray irradiation are found to vary with the Lu content.     

Yb3+/Er3+共掺(MLaFn)x(M=0,K;n=3,4;x=1,1.5)纳米材料的控制合成及其上转换发光性质

采用水热与溶剂热结合的方法,在乙二醇-正己醇体系中,通过调节KF与RE(RE=La,Yb,Er)的量比、反应温度和反应时间实现了由LaF_3(六角相)到KLaF_4(立方相、六角相)晶型的控制合成。借助透射电子显微镜(TEM)和X射线粉末衍射(XRD)对样品的结构和微观形貌进行表征。结果表明,当KF/RE比例为2. 25时,制备的样品为片状的六角相LaF_3纳米颗粒;当KF/RE比例为3. 00时,得到具有近似球形的立方相KLaF_4纳米颗粒;当KF/RE比例为4. 25时,得到了六角相(KLaF_4)_(1. 5)纳米颗粒。上转换发射光谱显示:所有的样品在近红外光(980 nm)激发下,均有3个明显的发射峰,在522 nm、544 nm处分别对应于Er~(3+)的~4S_(3/2),~2H_(11/2)→~4I_(15/2)能级跃迁,655 nm处属于Er~(3+)的~4F_(9/2)→~4I_(15/2)能级跃迁。     

Shaped crystal growth and scintillating properties of Yb:(Gd,Lu)3Ga5O12 solid solutions

Shaped single crystals of (Lu_xGd_1−x)₃Ga₅O₁₂ (0.0x1.0) and (Yb_0.05Lu_xGd_0.95−x)₃Ga₅O₁₂ (0.0x0.9) were grown by the modified micro-pulling-down method. Continuous solid solutions with garnet structure and a linear compositional dependency of crystal lattice parameter in the system Yb:(Gd,Lu)₃Ga₅O₁₂ are formed. Measured optical absorption spectra of the samples show 4f–4f transitions related to Gd³⁺ ion at 275 and 310 nm, and also an onset of charge transfer transitions from oxygen ligands to Gd³⁺ or Yb³⁺ cations below 240 nm. A complete absence of Yb³⁺ charge transfer luminescence under X-ray excitation in any of the investigated samples was explained by the overlapping of charge transfer absorption of Yb³⁺ by that of Gd³⁺ ions. For specific composition of Lu_1.5Gd_1.5Ga₅O₁₂ an intense defect-host lattice-related emission, which achieve of about 40% integrated intensity compared with Bi₄Ge₃O₁₂, was found.     

Upconversion studies in Er doped TeO2-M2O (M=Li, Na and K) binary glasses

The luminescence properties of Er³⁺ doped alkali tellurite [ TeO₂-M₂O (M=Li, Na and K)] glasses are investigated. Infrared to visible upconversion emissions are observed at 410, 525, 550 and 658 nm using 797 nm excitation. These bands are assigned to the ²H_9/2  →⁴I_15/2, ²H_11/2  →⁴I_15/2, ⁴S_3/2  →⁴I_15/2, ⁴F_9/2  →⁴I_15/2 transitions of Er³⁺ respectively. Detailed study reveals that the ²H_9/2  →⁴I_15/2 transition at 410 nm involves a three-step process while the other transitions involve two-steps. Excitation with 532 nm radiation gives additional bands at 380, 404, 475 and 843 nm wavelengths due to the ⁴G_11/2  →⁴I_15/2, ²P_3/2  →⁴I_13/2, ²P_3/2  →⁴I_11/2, and ⁴S_3/2  →⁴I_13/2 transitions, respectively, along with the bands observed on NIR excitation. The fluorescence yield is found to be largest for the TeO₂-Na₂O glass. The lifetime of the ⁴S_3/2 level has been measured for all the three cases and used to explain the upconversion mechanisms. The fluorescence intensity ratio corresponding to the two thermally coupled levels (²H_11/2, ⁴S_3/2) has been used to estimate the temperature of the glass. It is observed that the temperature sensing capacity of TeO₂-Li₂O glass is better than the other two glasses.     

Magnetism and hyperfine interactions of Fe, Eu, Gd, Dy, Er and Yb in RM4Al8 compounds (R = rare earth or Y, M = Cr, Mn, Fe, Cu)

Mössbauer and magnetic susceptibility studies of sixty tetragonal RM₄Al₈ compounds (R = 4f, M = 3d element), show a wide variety of magnetic phenomena in the behaviour of 3d transition elements. The rare earths order antiferromagnetically at temperatures below 10–30 K in all compounds. The 3d elements, however, all behave differently. Fe in RFe₄Al₈ has a localized moment (effective moment of 4.4 _μB) and orders independently of the rare earth sublattice. Mn in RMn₄Al₈ has also a localized moment (1 _μB) but orders only when the rare earths order. Cr in RCr₄Al₈ has no moment of its own, but it has an induced moment (.1 _μB) by its magnetic rare earth neighbours. Cu in RCu₄Al₈ is nonmagnetic. The Mössbauer studies of ¹⁵¹Eu, ¹⁵⁵Gd, ¹⁶¹Dy, ¹⁶⁶Er, ¹⁷⁰Yb and a ⁵⁷Fe probe yield all hyperfine interaction parameters including the orientation of the hyperfine field relative to the crystallographic c-axis. In addition, the studies yield the Ce, Eu and Yb valencies in the various compounds. Eu in EuFe₄Al₈ and in EuMn₄Al₈ and Yb in YbCr₄Al₈ are in a mixed valent state.     

Investigation of up-conversion luminescence properties of RE/Yb co-doped Y2O3 transparent ceramic (RE=Er, Ho, Pr, and Tm)

RE/Yb co-doped Y₂O₃ transparent ceramics (RE=Er, Ho, Pr, Tm) were fabricated and characterized from the point of up-conversion luminescence. All the samples exhibit high transparence not only in near-infrared band (NIR) band but also in visible region, which ensures the output of the up-conversion luminescence. Under 980 nm excitation, green and red emissions were observed in Er, Yb:Y₂O₃ transparent ceramic, while green emission was detected in Ho, Yb and Pr, Yb co-doped Y₂O₃ transparent ceramics. In Tm, Yb co-doped Y₂O₃ ceramic, very intense blue up-conversion luminescence was detected. The dependence of up-conversion emission intensity on the pumping power was measured for each RE/Yb co-doped Y₂O₃ transparent ceramic, and the up-conversion mechanism was discussed in detail. Meanwhile, the energy transfer efficiency was calculated.     

Mössbauer effect studies of RFe11Ti and RFe11TiH (R=Y,Gd, Er)

The Mössbauer spectra of ferromagnetic RFe₁₁Ti and RFe₁₁TiH_x   (R=Y$R=\mathrm{Y}$, Gd, Er, x=0$x=0$, 1) have been investigated in the temperature range 20–300 K and analysed in terms of a new model which allows a better fit of the spectra using less constraints than previously reported analyses. In addition to the dependence of magnetic hyperfine field and isomer shift on the number of Ti nearest-neighbours (NN) of the Fe atoms, this new model also considers the effect of the average interatomic distances between Fe atoms on the 8i, 8f and 8j crystallographic sites. Magnetic hyperfine fields were found to decrease with the average interatomic distances for Fe atoms on the same sites and with the same number of iron NN. This decrease was however lower than that due to the presence of one additional titanium NN. Furthermore the present model distinguishes the 8f from the 8j sites on the basis of the relative areas of the corresponding sextets. It leads to higher average magnetic hyperfine fields and isomer shifts for the 8f site as compared to the 8j sites which may be understood on the basis of electronic charge transfer between the rare-earth and Fe atoms. The dependence of hyperfine parameters on the number of titanium NN and on hydrogenation is similar to those previously reported.     

Facile Synthesis of Gd(OH)3‐Doped Fe3O4 Nanoparticles for Dual‐Mode T1‐ and T2‐Weighted Magnetic Resonance Imaging Applications

The facile hydrothermal synthesis of polyethyleneimine (PEI)‐coated iron oxide (Fe₃O₄) nanoparticles (NPs) doped with Gd(OH)₃ (Fe₃O₄‐Gd(OH)₃‐PEI NPs) for dual mode T₁‐ and T₂‐weighted magnetic resonance (MR) imaging applications is reported. In this approach, Fe₃O₄‐Gd(OH)₃‐PEI NPs are synthesized via a hydrothermal method in the presence of branched PEI and Gd(III) ions. The PEI coating onto the particle surfaces enables further modification of poly(ethylene glycol) (PEG) in order to render the particles with good water dispersibility and improved biocompatibility. The formed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs have a Gd/Fe molar ratio of 0.25:1 and a mean particle size of 14.4 nm and display a relatively high r₂ (151.37 × 10^?3m ^?1 s^?1) and r₁ (5.63 × 10^?3m ^?1 s^?1) relaxivity, affording their uses as a unique contrast agent for T₁‐ and T₂‐weighted MR imaging of rat livers after mesenteric vein injection of the particles and the mouse liver after intravenous injection of the particles, respectively. The developed Fe₃O₄‐Gd(OH)₃‐PEI‐PEG NPs may hold great promise to be used as a contrast agent for dual mode T₁‐ and T₂‐weighted self‐confirmation MR imaging of different biological systems.     

Correlation of photoluminescence of (Y, Ln)VO4:Eu (Ln=Gd and La) phosphors with their crystal structures

We have studied the photoluminescence (PL) of (Y, Ln)VO₄:Eu³⁺ (Ln=La and Gd) phosphors and the correlation of the PL of those phosphor with their crystal structure. It is found that (Y, Gd)VO₄:Eu³⁺ phosphors have the same crystal structure as YVO₄:Eu³⁺, which is tetragonal with a little different lattice parameters. In the case of (Y, La)VO₄:Eu³⁺ phosphors, however, the gradual change from tetragonal to monoclinic structure of host lattice was observed as the amount of La ion increased. To investigate the PL property of (Y, Ln)VO₄:Eu³⁺ (Ln=La and Gd) phosphors, vacuum ultraviolet (VUV) and ultraviolet (UV) excitation were used. The favorable crystal structure for the PL intensity of orthovanadate phosphor under 147 and 254 nm excitation was tetragonal containing Gd ion and under 365 nm excitation was monoclinic containing La ion which might have the lowest site symmetry for Eu³⁺ ion.     

Elastic and photo-elastic characteristics of laser crystals potassium rare-earth tungstates KRE(WO4)2, where RE = Y,Yb, Gd and Lu

The elastic and photo-elastic characteristics of four laser crystals KY(WO₄)₂, KGd(WO₄)₂, KYb(WO₄)₂, and KLu(WO₄)₂ are presented. The first pair was reported early, and the last two materials have been investigated for the first time. The full matrix of elastic constants of these monoclinic crystals has been determined. Also, acousto-optical figure of merit for all the basic geometries of isotropic diffraction has been measured. It is proved that potassium rare-earth tungstates has rather good acousto-optical properties and particularly can take place of fused silica in technical applications required high power laser radiation. All the results demonstrate good prospect of these optically bi-axial laser crystals for development of new effective acousto-optical devices.