水热法合成纳米晶NaYF4 : Er3+,Tm3+,Yb3+ 的上转换发光特性

以EDTA为络合剂,用水热法合成了Er³⁺,Tm³⁺和Yb³⁺共掺杂的NaYF₄纳米晶。XRD和TEM的结果表明:粒径约为30 nm,属于六方晶系。在980 nm半导体激光器激发下,研究了不同Er³⁺离子掺杂浓度对Tm³⁺和Er³⁺离子上转换发光性能的影响,光强与泵浦功率的双对数曲线表明,474,525,539,650 nm的发射均属于双光子过程,408 nm的发射属于三光子过程。讨论了样品的协作敏化和声子辅助共振能量传递的上转换发光机制。     

Intense red upconversion luminescence from Tm³⁺/Yb³⁺ codoped transparent glass ceramic

Tm³⁺/Yb³⁺ codoped transparent glass ceramic containing β-PbF₂ nanocrystals was successfully prepared. After thermal treatment, emissions from the ¹G₄ state of Tm³⁺ excited by 980 nm laser were greatly quenched by cross relaxation and the 700 nm luminescence from Tm³⁺:³F_2,3→³H₆ transition was strongly enhanced. A nearly monochromatic red luminescence band was observed. Based on the luminescence decay curves and Judd-Ofelt analysis, the strengthened cross relaxation played an important role in such phenomenon.     

Photonic generation of stable microwave signals from a dual-wavelength Al₂O₃:Yb³⁺ distributed-feedback waveguide laser

We report the fabrication and characterization of a dual-wavelength distributed-feedback channel waveguide laser in ytterbium-doped aluminum oxide. Operation of the device is based on the optical resonances that are induced by two local phase shifts in the distributed-feedback structure. A stable microwave signal at ～15 GHz with a -3?dB width of 9 kHz was subsequently created via the heterodyne photodetection of the two laser wavelengths. The long-term frequency stability of the microwave signal produced by the free-running laser is better than ±2.5 MHz, while the power of the microwave signal is stable within ±0.35 dB.     

Stereodynamics of the reactions Ne+H₂⁺/Ne+D₂⁺/Ne+T₂

The vector correlations between products and reagents for the reactions Ne+H + 2 , Ne+D + 2 , and Ne+T + 2 are calculated by means of the quasi-classical trajectory method on a new potential energy surface constructed by Lü et al. [J. Chem. Phys. 2010 132, 014303]. The polarization-dependent differential cross-sections (2π/σ)(dσ 00 /dω t ), (2π/σ)(dσ 20 /dω t ), (2π/σ)(dσ 22+ /dω t ), and (2π/σ)(dσ 21 /dω t ), and the distributions of P (θ r ), P (φ r ), and P (θ r ,φ r ) are calculated. The isotopic effect, which is associated with the difference in mass factor among the three reactions, is revealed.     

Spectroscopic properties in Er³⁺/Yb³⁺ Co-doped fluorophosphate glass

Using the technique of high-temperature melting, a new Er 3+ /Yb 3+ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er 3+ and Yb 3+ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd–Ofelt theory, the oscillator strength was computed. The lifetime of 4 I 13/2 level (τ m ) of Er 3+ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 μm. The large stimulated emission cross section of the Er 3+ was calculated by the McCumber theory. The spectroscopic properties of Er 3+ ion were compared with those in different glasses. The full width at half maximum and σ e are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.     

Diode-pumped laser and self-frequency-doubling properties of a Nd³⁺:Na₃La₉O₃(BO₃)₈ crystal

We report efficient, diode-pumped, self-frequency doubling (SFD) in the newly developed laser crystal Nd³⁺:Na₃La₉O₃(BO₃)₈ (Nd:NLBO). More than 730?mW of fundamental output power at 1072?nm was achieved with a slope efficiency of 16.2%. With incident pump power of 8?W, 29?mW of green cw laser emission at 536?nm was observed with proper phase matching. This initial performance and the good optical properties of the crystalline host are encouraging for the development of a high power diode-pumped SFD visible light laser source.     

Ca₂BO₃Cl:Ce³⁺,Tb³⁺:A novel tunable emitting phosphor for white light-emitting diode

<正>Ca₂BO₃Cl:Ce³⁺,Ca₂BO₃Cl:Tb³⁺,and Ca₂BO₃Cl:Ce³⁺,Tb³⁺ phosphors are synthesized by a high temperature solid-state reaction.The emission intensity of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl is influenced by the Ce³⁺ or Tb³⁺ doping content,and the optimum concentrations of Ce³⁺ and Tb³⁺ are 0.03 mol and 0.05 mol,respectively.The concentration quenching effect of Ce³⁺ or Tb³⁺ in Ca₂BO₃Cl occurs,and the concentration quenching mechanism is d-d interaction for either Ce³⁺ or Tb³⁺.The Ca₂BO₃Cl:Ce³⁺,Tb³⁺ can produce colour emission from blue to green by properly tuning the relative ratio between Ce³⁺ and Tb³⁺,and the emission intensity of Tb³⁺ in Ca₂BO₃Cl can be enhanced by the energy transfer from Ce³⁺ to Tb³⁺.The results indicate that Ca₂BO₃Cl:Ce³⁺,Tb³⁺ may be a promising double emission phosphor for UV-based white light emitting diodes.     

The concentration quenching and crystallographic sites of Eu²⁺ in Ca₂BO₃Cl

A yellow phosphor, Ca2BO3 Cl:Eu2+ , is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f 6 5d 1 →4f 7 transition of Eu2+ . Eu2+ ions occupy two types of Ca2+ sites in the Ca2BO3 Cl lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2+ in Ca2 BO 3 Cl. The emission intensity of Eu2+ in Ca2BO3 Cl is influenced by the Eu2+ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole–dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.     

Shifting bright spatial solitons in LiNbO₃

We observe spatial bright solitons in a transversely shifting LiNbO₃ crystal. In this scheme, the photovoltaic nonlinearity in LiNbO₃ can be switched from self-defocusing to self-focusing by continuous shifting of the beam. Moreover, the shifting velocity has a strong influence on the wave shape of the bright spatial solitons.     

Optical planar waveguides in Yb³⁺-doped phosphate glasses produced by He⁺ ion implantation

Optical planar waveguides in Yb 3+-doped phosphate glasses are fabricated by implanting triple-energy helium ions. The guiding modes and the near-field intensity distribution are measured by using the prism-coupling method and the end-face coupling setup with a He-Ne laser at 633 nm The intensity calculation method (ICM) is used to reconstruct the refractive index profile of the waveguide. The absorption and the fluorescence investigations reveal that the glass bulk features are well preserved in the active volumes of the waveguides, suggesting the fabricated structures for possible applications as waveguide lasers.     

Effects of swift argon-ion irradiation on the proton-exchanged LiNbO₃ crystal

A proton-exchanged LiNbO3 crystal was subjected to 70-MeV argon-ion irradiation.The lattice damage was investigated by the Rutherford backscattering and channeling technique.It was found that the lattice disorder induced by the proton exchange process was partially recovered and the proton-exchanged layer was broadened.It indicated that the lithium ions underneath the initial proton-exchanged layer migrated to the surface during the swift argon-ion irradiation and supplemented the lack of lithium ions in the initial proton-exchanged layer.This effect was ascribed to the great electronic energy deposition and relaxation.The swift argon-ion irradiation induced an increase in extraordinary refractive index and formed another waveguide structure beneath the proton-exchanged waveguide.     

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     

Evolution of the 251 cm^-1 infrared phonon mode with temperature in Ba_0.6K_0.4Fe₂As₂

The far-infrared optical reflectivity of an optimally doped Ba1-xKxFe2As2(x =0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1 . This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound.     

LiNbO<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript> crystals for optical temperature sensors

Possibilities of using lithium niobate crystals, doped with ytterbium (LN:Yb³⁺) as materials for optical temperature sensor (OTS), are discussed. We consider both the radiative and absorptive characteristics of the crystals, assuming that their temperature dependences are caused by the Boltzmann factor of the initial population of Stark sublevels of the ion. It is shown that the crystals can be used as materials for OTS in the temperature range 150–400 K.     

Upconversion blue emission dependence on the pump mechanism for Tm<Superscript>3+</Superscript>-heavy-doped NaY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Upconversion blue emissions of Tm³⁺-ion-heavy-doped NaY(WO₄)₂ crystals are investigated with three different near-infrared pump mechanisms. The dependence of upconversion efficiency on the pump mechanism is analyzed from the scope of the concentration quenching effect. Three cross-relaxation processes, , , and , which influence the upconversion dominantly in the Tm³⁺-heavy-doped system, are demonstrated theoretically and experimentally. The results indicate that Yb³⁺ ions can weaken the concentration quenching effect of Tm³⁺ ions significantly so that the blue emission efficiency can be enhanced by one order of magnitude. At the same time, the wavelength of the pump source also has considerable influence on both the population of some crucial energy levels and the upconversion mechanism. Experiments show that the upconversion blue emission in Tm³⁺/Yb³⁺ co-doped NaY(WO₄)₂ crystal under 980-nm laser diode excitation is the most intensive of these three different near-infrared pump mechanisms. The conclusions are confirmed by spectra measurements and calculations of Judd–Ofelt theory and Miyakawa–Dexter theory. PACS 42.70.Hj; 78.55.-m     

The phase transition,hygroscopicity, and thermal expansion properties of Yb_2-xAl_xMo₃O₁₂

Materials with the formula Yb 2-xAlxMo3O12(x =0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.8) were synthesized and their structures, phase transitions, and hygroscopicity investigated using X-ray powder diffrac- tion, Raman spectroscopy, and thermal analysis. It is shown that Yb2-xAlxMo3O12 solid solutions crystallize in a single monoclinic phase for 1.7 ≤ x ≤ 2.0 and in a single orthorhombic phase for 0.0 ≤ x ≤ 0.4, and exhibit the characteristics of both monoclinic and orthorhombic structures outside these compositional ranges. The monoclinic to orthorhombic phase transition temperature of Al2Mo3O12 can be reduced by partial substitution of Al 3+ by Yb3+, and the Yb2-x AlxMo3O12 (0.0 < x ≤ 2.0) materials are hydrated at room temperature and contain two kinds of water species. One of these interacts strongly with and hinders the motions of the polyhedra, while the other does not. The partial substitution of Al3+ for Yb3+ in Yb2Mo3O12 decreases its hygroscopicity, and the linear thermal expansion co- efficients after complete removal of water species are measured to be 9.1×10 6 /K, 5.5×10 6 /K, 5.74×10 6 /K, and 9.5 × 10 6 /K for Yb1.8 Al0.2 (MoO4)3 , Yb1.6Al0.4 (MoO4 )3, Yb0.4 Al1.6 (MoO4)3 , and Yb 0.2Al1.8 (MoO4)3 , respectively.     

溅射气氛和退火方式对硅纳米晶的形成及发光特性的影响

利用磁控溅射技术溅射硅靶,通过调节溅射气氛在硅衬底上生长了SiO/SiO₂超晶格,热退火处理后超晶格中的SiO发生相分离得到硅纳米晶。通过比较不同退火方式对于硅纳米晶的形成的影响发现,管式炉退火处理的样品给出非常强的室温光致发光,其发光峰的峰位随着硅纳米晶尺寸的增大而红移,且管式炉退火比快速热退火更有利于硅纳米晶的形成。     

10BaF₂:NaF,Na₃AlF₆/TiO₂ composite as a novel visible-light-driven photocatalyst based on upconversion emission

A rare-earth free upconversion luminescent material, 10BaF 2 :NaF, Na 3 AlF 6 , is synthesized by a hydrothermal method. The study of fluorescent spectrum indicates that it can convert visible light (550 nm–610 nm) into ultraviolet light (290 nm–350 nm), and two emission peaks at 304 nm and 324 nm are observed under the excitation of 583 nm at room temperature. Subsequently, 10BaF 2 :NaF, Na 3 AlF 6 /TiO 2 composite photocatalyst is prepared and its catalytic activity is evaluated by the photocatalytic reduction of CO 2 under visible light irradiation (λ > 515 nm). The results show that 10BaF 2 :NaF, Na 3 AlF 6 /TiO 2 is a more effective photocatalyst for CO 2 reduction than pure TiO 2 , their corresponding methanol yields are 179 and 0 μmol/g-cat under the same conditions. Additionally, the mechanism of photocatalytic reduction of CO 2 on 10BaF 2 :NaF, Na 3 AlF 6 /TiO 2 is proposed.     

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.     

Homogeneous interface-type resistance switching in Au/La_0.67Ca_0.33MnO₃/SrTiO₃/F:SnO₂ heterojunction memories

La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunctions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field- induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 × 10 4 % by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.