Effect of nanocrystals on up-conversion luminescence of Er3+,Yb3+ co-doped glass-ceramics

Different up-conversion luminescent spectra of Er3+ ions were observed in the oxyfluoride glass-ceramics.The ratio of two fluorides in the original compositions was modified in order to form different nanocrystals.The intensity of up-conversion luminescence increased sharply when the ratio of PbF2 and CdF2 was 40:10.The data of differential thermal analysis and X-ray diffraction were used to explain the optimization fluoride ratio. The intensity of up-conversion luminescence is not only decided by the crystallizability but also mainly related with the stoichiometric proportion of fluoride nanocrystals in the glass-ceramics.     

Enhancement of up-conversion luminescence in Zn2SiO4:Yb3+, Er3+ by co-doping with Li+ or Bi3+

Yb³⁺/Er³⁺ co-doped Zn₂SiO₄ ceramics are rapidly synthesized by the microwave radiation method. Green and red up-conversion emissions are observed in Zn₂SiO₄: Yb³⁺, Er³⁺ ceramics under 980 nm excitation. The influence of co-doped Li⁺ or Bi³⁺ ion on luminescence intensity for the phosphors has been investigated. At Li⁺ or Bi³⁺ doping concentration of 1 mol%, up-converted green emission can be increased by 6 times and 20 times, respectively. It is believed that co-doped Li⁺ or Bi³⁺ ion results in the local distortion of Er³⁺ in Zn₂SiO₄, increasing the intra-4f transitions of Er³⁺ ions. The local distortion is proved by spectral probing method with Eu³⁺.     

Up/down-conversion luminescence of monoclinic Gd2O3:Er3+ nanoparticles prepared by laser ablation in liquid

Multifunctional luminescent materials are attracting attention nowadays. In this work, monoclinic Gd₂O₃:Er³⁺ nanoparticles, which possess up-conversion luminescence and down-conversion luminescence properties, were successfully synthesized by laser ablation in liquid (LAL) technique. Up-conversion luminescence and down-conversion luminescence of monoclinic Gd₂O₃:Er³⁺ nanoparticles were got under the excitation of 980 nm and 379 nm, respectively. In addition, tunable luminescence was got. Furthermore, the cytotoxicity of the nanoparticles is low and the fluorescence of the nanoparticles in cell is also strong enough. The results indicate that the Gd₂O₃:Er³⁺ nanoparticles synthesized by LAL technique are promising candidates for bio-imaging or other fields that require controllable fluorescence.     

Ar环境下脉冲激光烧蚀粒子阻尼系数的空间分布

在10 Pa的Ar环境气体中,采用脉冲激光烧蚀技术,分别在半径为2.0,2.5,3.0,3.5和4.0 cm的半圆环不同角度处的衬底上制备了一系列含有纳米晶粒的Si晶薄膜。使用扫描电子显微镜、X射线衍射仪和拉曼光谱仪对其表面形貌和微观结构进行分析表征。结果表明,纳米Si晶粒的平均尺寸和烧蚀粒子的阻尼系数均相对于羽辉轴向呈对称分布,并随着与羽辉轴向夹角的增大而减小;同时,随着衬底半径的增加,晶粒平均尺寸和阻尼系数均逐渐减小。     

Ar环境下脉冲激光烧蚀粒子阻尼系数的空间分布

在10 Pa的Ar环境气体中,采用脉冲激光烧蚀技术,分别在半径为2.0,2.5,3.0,3.5和4.0 cm的半圆环不同角度处的衬底上制备了一系列含有纳米晶粒的Si晶薄膜。使用扫描电子显微镜、X射线衍射仪和拉曼光谱仪对其表面形貌和微观结构进行分析表征。结果表明,纳米Si晶粒的平均尺寸和烧蚀粒子的阻尼系数均相对于羽辉轴向呈对称分布,并随着与羽辉轴向夹角的增大而减小;同时,随着衬底半径的增加,晶粒平均尺寸和阻尼系数均逐渐减小。     

Synthesis and up-conversion luminescence properties of Ho3+, Yb3+ co-doped BaLa2ZnO5

Up-conversion phosphors BaLa₂ZnO₅ co-doped with Ho³⁺/Yb³⁺ were synthesized by high temperature solid-state reaction method. The phase composition of the phosphors was characterized by X-ray diffraction (XRD). The structure of BaLa₂ZnO₅: 0.75% Ho/15% Yb phosphor was refined by the Rietveld method and results showed the decreased unit cell parameters and cell volume after doping Ho³⁺ and Yb³⁺, indicating Ho³⁺ and Yb³⁺ have successfully replaced La³⁺. Under the excitation of 980 nm diode laser, the strong green and weak red up-conversion emissions centered at 548 nm, 664 nm and 758 nm were observed, which originating from ⁵S₂, ⁵F₂→⁵I₈, ⁵F₄→⁵I₈ and ⁵S₂, ⁵F₂→⁵I₇ transitions of Ho³⁺ ions, respectively. The optimum doping concentrations of Ho³⁺ and Yb³⁺ were determined to be 0.75% and 15%, and the corresponding Commission International de L'Eclairage (CIE) coordinates are calculated to be x=0.298 and y=0.692. The related UC mechanism of Ho³⁺/Yb³⁺ co-doped BaLa₂ZnO₅ depending on pump power was studied in detail. The results indicate that BaLa₂ZnO₅: Ho³⁺/Yb³⁺ can be an effective candidate for up-conversion yellowish-green light emitter.     

Nano-ionic thin films of gadolinia-doped ceria prepared by pulsed laser ablation

Microstructural properties of nano-ionic thin films of gadolinia-doped ceria (GDC) prepared by pulsed laser ablation from sintered targets of gadolinia (5–20 mol%) doped ceria are investigated. The ionic conductivity measurements of the sintered pellets showed a decrease in the activation energy from 1.1 to 0.65 eV for 5 and 30 mol% gadolinia-doped ceria, respectively. The microstructural properties of the GDC films as a function of substrate temperature, oxygen partial pressure, and laser energy show that the films are polycrystalline in the entire range of substrate temperature. The grain size is found to increase with increasing temperature up to 873 K. Further improved crystallinity is noticed for the films grown with oxygen partial pressure of 0.1–0.2 mbar. X-ray diffraction and transmission electron microscopy (TEM) reveal nanocrystalline grains with textured growth along <111> orientation in these films at low substrate temperature and at lower oxygen partial pressure. TEM study shows a uniform distribution of nanocrystal of 8–10 nm for energies ≤200 mJ/pulse, and nanocrystals embedded in a large crystalline matrix of doped ceria for energies in the range 400–600 mJ/pulse. Raman spectroscopy also confirms the defects in these films. The study also reveals that the substrate temperature and oxygen partial pressure could influence preferred orientation, while the laser energy could significantly influence defect concentration in these films. Invited paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Nd3+-doped LiYF4 thin films prepared by pulsed laser deposition

Nd:LiYF₄ (YLF) thin films were prepared on CaF₂ or YLF substrates by pulsed laser deposition, using a KrF laser for ablation of Nd:LiYF₄ single-crystal targets. For 10 J/cm², 450 °C and about 10^-6 mbar pressure, transparent and crystalline, highly textured, YLF films were obtained, without oxyfluoride or YF₃ contamination. High surface roughness is shown by optical microscopy and interface ion diffusion between film and substrate is evidenced by Rutherford backscattering spectroscopy. Fluorescence properties of the films are quite similar to those of bulk Nd:YLF crystal, which confirms the pure YLF composition and shows good conservation of Nd³⁺ ion doping rate. PACS 81.15.Fg; 68.55.Jk; 78.55.Hx     

Blue luminescent silicon nanocrystals prepared by short pulsed laser ablation in liquid media

The pulsed laser processing in liquid media is an attractive alternative to produce room temperature luminescent silicon nanocrystals (Si-ncs). We report on a blue luminescent Si-ncs preparation by using nanosecond pulsed laser (Nd:YAG, KrF excimer) processing in transparent polymer and water. The Si-ncs fabrication is assured by ablation of crystalline silicon target immersed in liquids. During the processing and following aging in liquids, oxide based liquid media, induce shell formation around fresh nanocrystals that provides a natural and stable form of surface passivation. The stable room temperature blue-photoluminescent Si-ncs are prepared with maxima located around ∼440 nm with corresponding optical band gap around ∼2.8 eV (∼430 nm). Due to the reduction of surface defects, the Si-ncs preparation in water, leads to a narrowing of full-width-half-maxima of the photoluminescence spectra.     

Investigation of pulsed laser ablation process of Hg0.8Cd0.2Te

The vaporization threshold was measured under the irradiation of 1.064-μm, 10-ns pulsed laser. Then we calculated the vaporization temperature based on the conservation law of energy and analyzed the vaporization time based on our established model. These results coincided well with the information from the micrograph of scanning electron microscope (SEM) and the spectra of the plasma. Besides, the laser ablation rate was also computed and discussed theoretically.     

High-sensitive terahertz detection by parametric up-conversion using nanosecond pulsed laser

A high-sensitive terahertz detector operating at room temperature was demonstrated based on parametric upconversion.A nanosecond 1064-nm Nd:YAG laser was used to pump the parametric up-conversion detector and the upconversion from terahertz wave to NIR laser was realized in a lithium niobate crystal.The minimum detectable terahertz energy of 9 p J was realized with the detection dynamic range of 54 d B,which was three orders of magnitude higher than that of commercial Golay cell.The detectable terahertz frequency range of the detection system was 0.90 Thz–1.83 THz.Besides,the effects of pump energy and effective gain length on the detection sensitivity were studied in experiment.The results showed that higher pump energy and longer effective gain length are helpful for improving the detection sensitivity of parametric up-conversion detector.     

Red luminescence of Eu3+ doped ZnO nanoparticles fabricated by laser ablation in aqueous solution

Fabrication of Eu³⁺-doped ZnO nanoparticles by laser ablation in liquid medium is reported. Sintered disks made of mixed powders of ZnO and Eu₂O₃ are used for targets, and surfactant of sodium dodecyl sulfate or LiOH is included in solution. Round-shaped nanoparticles with the diameter of 5??30?nm are synthesized. When the ZnO host is photoexcited, broad green photoluminescence (PL) of oxygen vacancies in the ZnO host as well as red PL of Eu³⁺ is observed at room temperature. The red PL peak of Eu³⁺ included in the ZnO host lattice is different from that of the source material of Eu₂O₃. Energy transfer from the ZnO host to Eu³⁺ is demonstrated in site-selectively excited PL spectra and its excitation spectra. This result shows that the liquid-phase laser ablation is useful for doping active centers into nanoparticles.     

Structure and up-conversion luminescence of Pr~(3+)/Yb~(3+) co-doped Ca Nb_2O_6 thin films by pulsed laser deposition

Pr3t∕Yb3tco-doped Ca Nb2O6 thin films are deposited on Si(100) substrates by pulsed laser deposition and annealed at different temperatures in air atmosphere. X-ray diffraction, Raman spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and photoluminescence spectra are used to characterize the samples. The results show that the annealing temperature has a strong effect on the film's grain size, structure,morphology, and the up-conversion luminescence properties. The grain size and up-conversion luminescence of Pr3t∕Yb3tco-doped Ca Nb2O6 films increases with the increasing annealing temperature.     

Morphology and crystalline-phase-dependent luminescence of Li-doped Gd2O3:Eu3+ thin films grown by pulsed laser deposition

Gd₂O₃:Eu³⁺ and Li-doped Gd₂O₃:Eu³⁺ luminescent thin films have been grown on Si(100) substrates using pulsed laser deposition. The films grown at different deposition conditions show different crystalline and morphology structures and luminescent characteristics. Although both cubic and monoclinic crystalline structures were observed in both Gd₂O₃:Eu³⁺ and Li-doped Gd₂O₃:Eu³⁺ films, the cubic structure becomes more dominant for Li-doped Gd₂O₃:Eu³⁺ films. The photoluminescence brightness data obtained from Li-doped Gd₂O₃:Eu³⁺ films indicate that Si(100) is a promising substrate for growth of high-quality Li-doped Gd₂O₃:Eu³⁺ thin-film red phosphor. In particular, the incorporation of Li⁺ ions into the Gd₂O₃ lattice induced a change of crystallinity and enhanced surface roughness. Two major factors to determine photoluminescence brightness for Li-doped Gd₂O₃:Eu³⁺ films were crystalline phase and surface roughness. The highest emission intensity was observed with Gd_1.84Li_0.08Eu_0.08O₃, whose brightness was a factor of 2.1 larger than that of Gd₂O₃:Eu³⁺ films. This phosphor is promising for applications in flat-panel displays. PACS 78.20.-e; 78.55.-m; 78.66.-w     

Tm3+/Yb3+共掺氟氧硅铝酸盐玻璃陶瓷蓝色上转换发光研究

按摩尔百分比制备了组分为30S102.(20-x-y)Al2O3-4OPbF2-1OCdF2-xTm2O3-yYb2O3的两组Tm3 ,Yb3 共掺杂氟氧硅铝酸盐上转换蓝色发光玻璃陶瓷材料,测量了其在980nm激光激发下的上转换发光光谱,分析了此材料中Tm3 /YI)3 发光体系的上转换发光机理,并系统地研究了Tm3 离子和Yb3 离子的浓度对该材料上转换发光性能的影响.研究表明:由于Tm3 离子之间存在着交叉弛豫作用使得蓝光(477nm)发光强度随Tm3 离子浓度增加而减弱,实验获得的最佳掺杂浓度为x=0.025(mol%);另外,在Tm3 /Yb3 上转换发光体系中,Yb3 离子合作上转换能量传递过程和三光子过程是共同存在的,随着yb3 离子浓度的增加,Tm3 离子3H4能级到Yb3 离子2F5/2能级的反向能量传递增强使3H4能级上粒子布居数不断减少,三光子过程作用减弱;但是Yb3 离子合作上转换能量传递过程则发挥越来越大的作用,使上转换蓝光强度总体上不断增加.     

共沉淀法制备Y2SiO5∶Er3+ ,Yb3+ ,Tm3+及其上转换发光性能研究

采用化学共沉淀法制备了系列Y_1.98-2xYb_2x Er_0.02SiO₅(0.00≤x≤0.15)以及Y_1.736Yb_0.24Er_0.02Tm_0.004SiO₅上转换发光材料,比较了室温下Y_1.98-2xYb_2x Er_0.02 SiO₅ (x=0.00,0.08)样品在400—1600 nm范围内的吸收光谱,测量了所有样品在976 nm OPO激光器激发下的上转换发射光谱,以及Er³⁺离子⁴S_3/2(⁴F_9/2)→⁴I_15/2,Tm³⁺离子¹G₄→³H₆荧光衰减曲线和不同激发功率下的上转换蓝光发射强度,从而分析讨论了Er³⁺,Tm³⁺在Y₂SiO₅中的上转换发光机理.研究结果表明:在1250 ℃相对较低的温度下合成了X2型单斜晶系Y₂SiO₅ ∶Ln³⁺(Ln³⁺=Er³⁺,Yb³⁺,Tm³⁺),Yb³⁺的敏化显著增强了样品在976 nm附近的吸收能力,并大幅度加宽了该处的吸收带.分析上转换发射光谱发现:上转换绿光和红光强度都随着Yb³⁺浓度的增加先增强后减弱,但红光的猝灭浓度较高,归因于Er³⁺→Yb³⁺反向能量传递ETU4和Yb³⁺→Er³⁺正向能量传递ETU3过程的发生;上转换蓝光发射是三光子吸收过程,是通过Yb³⁺,Tm³⁺之间三次声子辅助的能量转移方式实现的. 关键词： 上转换 共沉淀 2SiO₅∶Er³⁺')" href="#">Y₂SiO₅∶Er³⁺ 3+')" href="#">Yb³⁺ 3+')" href="#">Tm³⁺     

Visible photoluminescence from hydrogenated amorphous carbon films prepared by pulsed laser ablation of polymethyl methacrylate (PMMA)

Visible photoluminescence (PL) has been observed from the hydrogenated amorphous carbon (a-C:H) films prepared by ArF pulsed laser ablation of polymethyl methacrylate (PMMA) in the presence of hydrogen gas (H₂). With increasing hydrogen concentration the PL intensity increases and the intensity maximum blue-shifted. The PL intensity also increases after hours of light illumination, exhibiting a light soaking enhancement. Increasing the deposition temperature decreases the PL and increases the ratio of sp³/sp² bonds.Z.F. Li is on leave from Department of Physics, Nanjing University, Nanjing 210093, P.R. China.     

Successive preparation of decorated zinc oxide organic sol by pulsed laser ablation and their luminescence characteristics

Nano-ZnO organic sols which were modified in situ were successively produced through focused pulsed laser ablation of ZnO target in interface of solid and flowing liquid which contained modification agents or polymer. It is found that the ZnO ethanol sol decorated by Q (8-hydroxylquinoline) radiates intense green light under ultraviolet radiation and has a broad emission band centered at 555 nm in the emission fluorescence spectrum. The influence of factors including different modification agents and their added methods, laser fluence, aging time after preparation, compositions of flowing liquid and their velocity on luminescence characteristics of nano-ZnO organic sol was characterized by TEM, UV-vis and fluorescence spectrum.     

脉冲激光烧蚀制备纳米Si晶粒成核气压阈值及动力学研究

采用脉冲激光烧蚀技术,在室温、低压Ar气条件下通过改变气体压强及靶与衬底间距,对纳米Si晶粒成核的气压阈值进行了研究.根据扫描电子显微镜图像、拉曼散射谱和X射线衍射谱对制备样品的表征结果,确定了在室温、激光能量密度为4 J/cm²、靶与衬底间距为3 cm条件下形成纳米Si晶粒的阈值气压为0.6 Pa.结合流体力学模型和成核分区模型,对纳米晶粒的成核动力学过程进行了分析.通过Monte Carlo数值模拟,表明在气相成核过程中,烧蚀Si原子的温度和过饱和密度共同影响着纳米晶粒的成核. 关键词： 脉冲激光烧蚀 成核 气压阈值 Monte Carlo数值模拟