NaYF4:Er3+和NaYF4:Yb3+/Er3+上转换荧光纳米晶的制备与表征

以EDTA为螯合剂,采用络合共沉淀法合成了NaYF4:Er3+和NaYF4:Yb3+/Er3+纳米晶.分别采用XRD、SEM、荧光分光光度计对合成的样品进行了结构、形貌和上转换荧光分析.XRD结果表明,制备的NaYF4:Er3+和NaYF4:Yb3+/Er3+均为纯立方相;SEM结果显示,制备的NaYF4:Er3+和NaYF4: Yb3+/Er3+晶粒粒径都在100nm左右,与NaYF4:Er3+相比,NaYF4:Yb3+/Er3+晶粒尺寸分布更均匀,分散性更好,符合作为荧光标记材料的要求;上转换荧光分析表明,在980nm激光器激发下,NaYF4:Yb3+/Er3+的发光强度比NaYF4:Er3+提高了1个数量级.     

Tuning of crystal phase and luminescence properties of Gd2(MoO4)3:Dy3+ phosphors

The orthorhombic and monoclinic Gd₂(MoO₄)₃:Dy³⁺ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd₂(MoO₄)₃:Dy³⁺ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd₂(MoO₄)₃:Dy³⁺ were discussed. The electric dipole–dipole interaction between Dy³⁺ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd_1.84(MoO₄)₃:Dy_0.16³⁺ can be considered as a suitable candidate for white light emitting diodes (W-LEDs).     

微波水热合成六方相NaYF4以及Yb3＋、Er3＋掺杂NaYF4微米管

为了合成单相以及Yb3+、 Er3+掺杂的六方结构NaYF4,采用微波水热的方法,以稀土硝酸盐、氟化钠、柠檬酸、氢氧化钠、乙酸乙酯和水为原料,合成了六方相NaYF4以及Yb3+、Er3+掺杂的六方相NaYF4 (NaYF4 ∶ Yb3+,Er3+)微米管. 利用XRD、SEM对所得样品的物相和形貌进行了表征. 研究了不同反应条件对产物形貌和物相的影响,并提出了NaYF4微米管的形成机理. 研究发现,采用微波加热的方法可以在较低的温度下快速得到单一六方相的NaYF4. 所制备的Yb3+、 Er3+掺杂NaYF4微米管的上转换发光性能与其体材料类似,具有较高的发光强度.     

Photoluminescence of Y0.6Gd0.4NbO4:Eu3+/Tb3+ micrometric phosphors derived from hybrid precursors

Y_0.6Gd_0.4NbO₄: × Eu³⁺/Tb³⁺ mol% phosphors with different dopant concentrations have been synthesized by a modified wet-chemical technology named as in-situ chemical co-precipitation from multicomponent hybrid precursors. Their microstructure, micromorphology and particle sizes have been analyzed by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). Those phosphors present interesting morphology, just like “cobblestone” with about 1.0 μm in dimension. Besides this, the dependence of the Red to Orange (RO) emission for Eu³⁺ and the Green to Blue (GB) emission for Tb³⁺ in Y_0.6Gd_0.4NbO₄ host together with other fluorescent properties on the activator concentration has been discussed. It was shown that the RO value of Eu³⁺ varies much with the doping concentration, but the GB value of Tb³⁺ almost remains constant.     

Improved route for the synthesis of colloidal NaYF4 nanocrystals and electron spin resonance of Gd3+ local probe

This paper presents the synthesis and characterization of colloidal NaYF4 and NaYF4:20% Gd lanthanide nanocrystals. The nanoparticles were prepared by chemical route using co-thermolysis of Na(CF3COO), Y(CF3COO)3 and Gd(CF3COO)3 precursor in oleylamine surfactant/phenylether at Ts = 250 degrees C. By tuning the precursor/surfactant molar ratio during the process, it was possible to control the crystalline phase, chemical order and size of the nanocrystals. The nanocrystals were characterized by Transmission Electron Microscopy, Small Angle X-ray Scattering, powder X-ray Diffraction, dc-magnetization and Electron Spin Resonance (ESR) techniques. The ESR experiments show the so called U-spectrum for the Gd3+ ions in bulk counterpart materials, where characteristic powder spectra of cubic and lower crystal field symmetries were observed.     

Nd3+掺杂的NaYF4:Yb@NaYF4:Ho上转换纳米颗粒的光谱分析

上转换纳米颗粒因具有良好的穿透深度和发光强度被广泛地应用在生物标记或生物成像中。实验制备了核壳结构的NaYF₄:Yb@NaYF₄:Ho纳米颗粒, 分散均匀, 粒径在50 nm左右。通过光谱分析可知, 该纳米颗粒可在980 nm激光激发下发射波长为650 nm为主的发射光。进一步对该核壳结构的NaYF₄:Yb@NaYF₄:Ho纳米颗粒进行Nd³⁺掺杂, 制备了可被800 nm激光激发且发射强红光的纳米颗粒。通过比较多种不同结构的Nd³⁺掺杂NaYF₄:Yb@NaYF₄:Ho纳米颗粒的荧光光谱发现, NaYF₄:Yb@NaYF₄:Ho,Nd纳米颗粒发射光最强, 表明Nd³⁺掺杂在NaYF₄:Yb@NaYF₄:Ho纳米颗粒的壳层中最佳。最后对NaYF₄:Yb³⁺50%@NaYF₄:Ho³⁺1%,Nd³⁺x%纳米颗粒Nd³⁺离子的掺杂浓度进行优化, 实验结果表明: Nd³⁺掺杂浓度为30%时,该纳米颗粒在800 nm激光激发下发光强度最强。     

纳米NaYF4:Er3+,Yb3+上转换材料的合成及其性质研究

采用溶胶-凝胶法在水相合成了纳米NaYF_4:Er~(3 ),Yb~(3 )上转换材料,980nm红外激光照射下,肉眼可观察到明亮的上转换发光。实验研究了铒、镱掺杂浓度及焙烧温度对材料合成的影响。所合成的纳米材料呈圆球形、颗粒均匀、分散性好,平均粒径70nm,可应用于生物标记。     

Core/shell structured NaYF4:Yb3+/Er3+/Gd+3 nanorods with Au nanoparticles or shells for flexible amorphous silicon solar cells

A simple approach for preparing near-infrared (NIR) to visible upconversion (UC) NaYF4:Yb/Er/Gd nanorods in combination with gold nanostructures has been reported. The grown UC nanomaterials with Au nanostructures have been applied to flexible amorphous silicon solar cells on the steel substrates to investigate their responses to sub-bandgap infrared irradiation. Photocurrent–voltage measurements were performed on the solar cells. It was demonstrated that UC of NIR light led to a 16-fold to 72-fold improvement of the short-circuit current under 980 nm illumination compared to a cell without upconverters. A maximum current of 1.16 mA was obtained for the cell using UC nanorods coated with Au nanoparticles under 980 nm laser illumination. This result corresponds to an external quantum efficiency of 0.14% of the solar cell. Mechanisms of erbium luminescence in the grown UC nanorods were analyzed and discussed.     

Luminescent properties of YAl3(BO3)4:Eu3+ phosphors

YAL₃(BO₃)₄:Eu³⁺ phosphors were fabricated by the sol-gel method. The structure properties were measured by x-ray diffraction (XRD) and infrared spectra (IR). Doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors of 0, 1, 3, 4, and 5 mol% were studied. The excitation spectra and emission spectra of YAL₃(BO₃)₄:Eu³⁺ phosphors were examined by fluorescent divide spectroscopy (FDS). The luminescent properties of YAL₃(BO₃)₄:Eu³⁺ phosphors are discussion. The optimal doping concentration of Eu³⁺ ions in YAL₃(BO₃)₄:Eu³⁺ phosphors was found to be approximately 3 mol%.     

Sensitized upconversion emissions of Tb3+ by Tm3+ in YF3 and NaYF4 nanocrystals

Yb3+-Tm3+-Tb3+-codoped YF3 and NaYF4 nanocrystals (NCs) were synthesized using a simple hydrothermal method. Under 980 nm excitation, violet and ultraviolet upconversion (UC) emissions of 5D3 --> 7FJ (J = 6, 5, 4) and 5D4 --> 7FJ (J = 6, 5, 4, 3) of Tb3+ ions were observed with the fluoride NCs. In the Yb-Tm-Tb codoped NCs, energy transfer (ET) processes from Tm3+ to Tb3+ were proposed to be the main mechanisms for the UC emissions of Tb3+ ions. They are more efficient than the phonon assisted cooperative sensitization of the Yb3+ couple proposed previously for similar material system. The analysis of power dependence indicated that populating the 5D4 level of the Tb3+ ions was a four photon UC process, which demonstrated the existence of the two step ET process of Yb3+ --> Tm3+ --> Tb3+. It was also found that UC luminescence properties of Tb3+ ions were sensitive to crystal structures.     

Synthesis of colloidal upconverting NaYF4: Er3+/Yb3+ and Tm3+/Yb3+ monodisperse nanocrystals

The synthesis, characterization, and spectroscopy of upconverting lanthanide-doped NaYF4 nanocrystals (NCs) is presented. The monodisperse cubic NaYF4 NCs were synthesized via a thermal decomposition reaction of trifluoroacetate precusors in a mixture of technical grade chemicals, octadecene and the coordinating ligand oleic acid. In this straightforward method, the dissolved precursors are added slowly to the reaction solution through a stainless-steel canula resulting in highly luminescent nanocrystals with an almost monodisperse particle size distribution. The NCs were characterized through the use of transmission electron microscopy, selected area electron diffraction, 1H NMR, powder X-ray diffraction, and high-resolution luminescence spectroscopy. The NaYF4 NCs are capable of being of dispersed in nonpolar organic solvents thus forming colloidally stable solutions. The colloids of the Er3+, Yb3+ and Tm3+, Yb3+ doped NCs exhibit green/red and blue upconversion luminescence, respectively, under 980 nm laser diode excitation with low power densities.     

Effect of Gd3+ substitution on dielectric behaviour of copper-cadmium ferrites

The dielectric constant, , loss tangent (tan ) and a.c. resistivity (_a.c.) are measured in the frequency range of 100 Hz to 5 MHz for the series of samples Cd _x Cu_1–x Fe_2–y Gd _y O₄ prepared by the ceramic technique. The dispersion in for all the values of x and y=0 and 0.1 shows a normal behaviour except for y=0.1 and x=0.4. The lowering of dielectric intensity in substituted ferrites (y=0.1) and fast dispersion of (_a.c.) with frequency, are explained as due to the reduced number of Fe³⁺ participating in the polarization process and the hindrances caused by Gd³⁺ to the polarization process by localizing Fe²⁺ ions thereby increasing the resistivity and activation energy. The dispersion in tan for unsubstituted samples (y=0.0) shows a normal trend while substituted samples (y=0.1) show relaxation behaviour, which is explained by existing theories.     

Synthesis and luminescent properties of spindle-like CaWO4:Sm3+ phosphors

Spindle-like CaWO₄:Sm³⁺ phosphors were prepared via a Polyvinylpyrrolidone (PVP)-assisted sonochemical process, and characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectroscopy (PL). The XRD results suggested that the prepared samples are single-phase. The FE-SEM images indicated that the prepared CaWO₄:Sm³⁺ phosphors are composed of many spindles with maximum average diameter of 150 nm and maximum average length of 500 nm. Under 404 nm excitation, the characteristic emissions corresponding to ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2 and 11/2) transitions of Sm³⁺ in CaWO₄ phosphors were observed. The color coordinates for 1 mol% Sm³⁺ doped CaWO₄ phosphor were calculated to be (0.595, 0.404). The fluorescent concentration quenching of Sm³⁺ doped spindle-like phosphors was studied based on the Van Uitert's model, and it was found that the electric dipole–dipole (D–D) interaction is the dominant energy transfer mechanism between Sm³⁺ ions in the CaWO₄:Sm³⁺ phosphors. The critical energy transfer distance was estimated.     

Effect of Zr4+ and Si4+ substitution on the luminescence properties of CaMoO4:Eu3+ red phosphors

A series of intense red emitting phosphors, Ca_0.8?x Zr _x Mo_1?x Si _x O₄:0.2Eu³⁺ (x = 0.025, 0.05, 0.075, 0.1) that could be effectively excited in the UV region was prepared by conventional high temperature solid state reaction route. Structural, morphological and photoluminescence properties of the prepared samples were studied in detail. The incorporation of Zr⁴⁺ and Si⁴⁺ ions in CaMoO₄ lattice maintained the powellite crystal structure. Luminescence properties were optimized for 7.5 mol% of Zr⁴⁺ and Si⁴⁺ concentration. Emission intensities improved more than twice in comparison with CaMoO₄:Eu³⁺. Life times of the prepared samples improved and the quantum efficiency enhanced to ~39 %. The improvement in emission intensity and quantum efficiency is explained in terms of the local distortion around the Eu³⁺ ions resulting in improved absorption in the UV region. The CIE color co-ordinates of the red emission were in agreement with the values of the standard red phosphors providing potentiality to be used in phosphor converted (pc) white LEDs.     

Liquid phosphors POCl3-ZrCl4-235UO 2 2+ -Nd3+

Liquid phosphors POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ and POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ with concentrations of Nd³⁺ and UO ₂ ²⁺ of up to 0.75 and 0.12 M were prepared; the lifetime of the Nd³⁺ luminescence was up to 300 μs. The lifetime of the Nd³⁺ luminescence in POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions decreases with increasing neodymium concentration, and this decrease is more pronounced than that in POCl₃-ZrCl₄-Nd³⁺ solutions. At molar ratio [ZrCl₄]/[Nd³⁺] < 1.5, the luminescence lifetime sharply decreases with decreasing ZrCl₄ concentration. The intensity of the absorption bands of the OH groups observed in the near-IR range of the absorption spectra of POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions increases with increasing neodymium concentration. Upon storage of POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions for 2 years without contact with the environment, the intensity of the IR absorption bends of the OH groups gradually increases, whereas the lifetime of the Nd³⁺ luminescence decreases to 60-80 μs.     

Influence of sintering temperature on photoluminescence of Gd2O3:Eu3+ phosphors prepared by liquid phase reaction method

Nanostructured materials with diameters less than 100 nm have been studied vigorously in recent years. Many studies have been devoted on exceptional optical properties induced by quantum confinement for fundamental research and applications. For excellent luminescence characteristics, phosphor particles have to acquire fine size, narrow size distribution, non-aggregation, good crystalline, and spherical morphology. A liquid-phase reaction method was chosen in this study due to the low reaction temperature. Gd2O3:Eu3+ phosphors were synthesized by the liquid-phase reaction method and the effect of activation temperature on optical properties of the phosphors was investigated.     

Up-conversion luminescence of the NaYF4:Yb3+,Er3+ nanomaterials prepared with the solvothermal synthesis

Up-converting NaYF₄:Yb³⁺,Er³⁺ (x_Yb: 0.20, x_Er: 0.02) nanomaterials were prepared with a microwave assisted solvothermal synthesis to study how the synthesis parameters affect the structure and up-conversion luminescence of the materials and thus their usability as labels in biomedical applications. The purity of the materials was studied with Fourier transform infra-red (FT-IR) spectroscopy and the particle size and morphology with transmission electron microscopy (TEM). The crystal structure was characterized with X-ray powder diffraction (XPD) and the crystallite sizes were calculated with the Scherrer formula. Up-conversion luminescence and luminescence decays were studied with near infra-red (NIR) laser excitation at 970 nm.The presence of the oleic acid was observed in the FT-IR spectra. The TEM images showed small quasi-spherical nanoparticles as well as long nanorods. The XPD measurements revealed that both cubic and hexagonal forms of NaYF₄ were present in the materials. The crystallite sizes ranged from ca. 20 to over 150 nm for the cubic and hexagonal phases, respectively. The characteristic up-conversion luminescence of Er³⁺ in red (640–685 nm; ⁴F_9/2 → ⁴I_15/2) and green (515–560 nm; ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transitions) wavelengths was observed. The most intense luminescence and the longest luminescence emission lifetime were obtained with the material annealed for 12 h at 177 °C with 1.8 MPa pressure due to the predominance of the well-crystallized hexagonal form of NaRF₄ (R: Y, Yb, Er).