不同晶型氧化铝的YAG:Ce^(3+)荧光粉的制备、结构与性能研究

采用高温固相法合成了不同晶型氧化铝的YAG:Ce^(3+)荧光粉样品,通过对其荧光光学性能的考察发现:CS-α-Al_2O_3-YAG具有更好的荧光性能,这可能与其发光基质的晶相组成和晶相生长发育情况有关。研究表明:CS-α-Al_2O_3原料本身具有结晶度好,孔道结构表面积大的特点;由其合成的YAG:Ce^(3+)荧光粉中的发光基质YAG相单一,晶粒圆润,晶体结构完整。

Spectral Property and Thermal Quenching Behavior of Tb^(3+)-Doped YAG:Ce Phosphor

A series of YAG：Ce,Tb phosphors were synthesized by vacuum sintering method.Moreover,their spectral properties,thermal quenching behaviors and color rendering properties were investigated systematically.The photoluminescence emission spectra of YAG：Ce,Tb show a great red shift compared with that of YAG：Ce.Direct energy transfer from Tb^（3＋） to Ce^（3＋） ions is verified based on the analysis of different photoluminescence spectra.The quenching temperature for Tb^（3＋）-doped YAG：Ce phosphors is about 490 K.The thermal activation energy is estimated to be 0.18 and 0.291 eV for Tb^（3＋）-doped YAG：Ce and YAG：Ce phosphors,respectively.The smaller activation energy for Tb^（3＋）-doped YAG：Ce means a more rapid nonradiative transition from 5d to 4f state,thus resulting in the lower quenching temperature.In addition,white LEDs with improved color rendering properties are achieved by using modified YAG：Ce,Tb phosphors.

Local Structure Mediation and Photoluminescence of Ce^(3+)-and Eu^(3+)-Codoped YAG Nanophosphors

Cerium and europium codoped yttrium aluminum garnet（YAG：Ce,Eu） nanophosphors were prepared by sol-gel method.We systematically explored the structure,composition,morphology and photoluminescence（PL） properties by using X-ray diffraction,scanning electron microscope,high resolution transmission electron microscope,energy dispersive spectrometer,photoluminescence emission and excitation spectra techniques,and focused on clarifying the change of local structure surrounding Ce^3＋ ions by utilizing advanced quantitative ^27Al magic angle spinning nuclear magnetic resonance spectroscopy.The results show that the lattice constant slightly increases as the Ce^3＋ and Eu^3＋ ions incorporate,and the geometric distortion of local structure surrounding Ce^（3＋） activator introduced by the incorporated Eu^（3＋） coactivator causes the variation of crystal field,which results in red shift of Ce^3＋ PL emitting in YAG：Ce,Eu nanophosphor.Furthermore,the YAG：Ce,Eu nanophosphors could exhibit several sharp and narrow ^5D0 → ^7FJ（J = 1-4） emissions of Eu^3＋ ion besides the classic broad ^5d1 → ^4f（^2F（5/2）,^2F（7/2）） emissions of Ce^3＋ ion under near ultraviolet（UV） excitation.

YAG∶Ce Phosphors for WLED via Nano-Pesudoboehmite Sol-Gel Route

The sub-micron sized YAG ： Ce phosphors were synthesized via a modified sol-gel method by peptizing nano-pesudoboehmite particulate. It is found that YAG phase from the dried gel powders appears at 1000 ℃ then the pure YAG phase exists at a relatively lower sintering temperature of 1400 ℃. The smaller sizes of phosphors in the ranges of 1 - 3 μm are obtained due to the contribution of seeding effects of nano-sized alumina particles to strengthen each step of the processes. Both the excitation and emission spectra of photoluminescence of the phosphor obtained at 1400 ℃ meet well with the spectroscopic requirements of the WLED phosphors.

Structural and Optical Properties of Ce^(3+), Yb^(3+) Co-doped YAG Films by Pulsed Laser Deposition

Ce3＋, Yb3＋ co-doped Y3Al5O12 films were prepared by pulse laser deposition. X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence spectra were used to characterize their structural and luminescent properties. Near-infrared quantum cutting from the films was observed via a cooperative energy transfer from Ce3＋ to Yb3＋ ions. The high quantum efficiency of the films implies that Ce3＋,Yb3＋ co-doped Y3A15O12 films have potential application by tuning the solar spectrum to enhance the efficiency of silicon solar cells.

Relationship between Crystal Structure and Luminescence Properties of (Y_(0.96-x)Ln_xCe_(0.04))_3Al_5O_(12) (Ln=Gd, La, Lu) Phosphors

The doping effects of La^3＋, Gd^3＋ and Lu^3＋ on the crystal structure and luminescence properties of （Yo96-x LnxCe0.04）3Al5O12（Ln = Gd, La, Lu） phosphors were studied. The X-ray diffraction patterns presented that with the inerease of the doping concentrations of La^3＋ and Gd^3＋ ions, the d-value of （Y0.96-xLnxCe0.04）3Al5O12 （Ln = Gd, La） inereased and the larger the doping ion, the stronger the effect would be. The doping amount causing phase transition in （Y0.96-xLnxCe0.04）3Al5O12 decreased with the inerease of the ionic radii of the doping lanthanide ions （La^3＋： 0.106 nm, Gd^3＋： 0. 094 nm, Lu^3＋ ： 0.083 nm）. The bigger doping ion of Gd^3＋ made the emission of （Y0.96-xGdxCe0.04）3Al5O12 move to red spectral region, but the smaller one of Lu^3＋ made it blue.

Citrate sol-gel combustion preparation and photoluminescence properties of YAG:Ce phosphors

Yellow-emitting YAG：Ce3＋ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions （MRCM）, pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 ℃. The phosphors exhibited the charactefistc broadband visible luminescence of YAG：Ce. The optimum concentration of Ce3＋ was 1.0 tool.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole （d-q）. Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower tem- perature. The Y3Al5O12：Ce0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG：Ce.

Photoluminescence enhancement of YAG:Ce^(3+) phosphor prepared by co-precipitation-rheological phase method

YAG：Ce3＋ phosphor was prepared by a novel co-precipitation-rheological phase method.The resulting YAG：Ce3＋ phosphor was characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM） and photoluminescent emission spectra.By using acetic acid as solvent,YAG：Ce3＋ powder with small particle size（≤2 μm） was obtained at a relatively lower sintering temperature of 1400 oC.With the content of acetic acid increasing,small particles dissolved and disappeared,but larger particles grew up and changed its shape from spherical to partially rectangular.Meanwhile,the emission intensity of the sample prepared by co-precipitation-rheological phase method was about 43% higher than that of the sample prepared by co-precipitation method.It was assumed that the significant improvement of luminescence was mainly because the rheological phase presented a better diffusion environment,and therefore,a better homogeneity of activators of Ce3＋.

Synthesis and characterization of nano-sized YAG:Ce,Sm spherical phosphors

YAG：Ce,Sm spherical phosphors were synthesized by malic acid sol-gel method. The formation process of crystalline was characterized by X-ray diffraction （XRD） technique. The influence of Sm3＋ doping on the luminescent intensity and the morphology of phosphors were studied by fluorescence spectrum and scanning electron microscopy （SEM） techniques, respectively. The results indicated that the size of spherical powders was about 100 um calcined at 1200 ℃ for 3 h. The emission spectra of phosphors showed gradual red-shift from 525 to 540 um with the increase of doping concentration of Sm3＋ ion. A broadband emission specmtm of Ce3＋ ion appeared at 540 nm, and a series of emission peaks corresponding to the 4Gs/2-＋6Hd transition of Sm3＋ ion also appeared at 617 um with the doping of Sm3＋. The red component of YAG：Ce phosphors increased with the doping of Sm3＋.

Photoluminescence properties of YAG:Ce3+,pr3+nano-sized phosphors synthesized by a modified co-precipitation method

Abstract： Monophasic Ce3＋ and Pr3＋ co-doped yttrium aluminum garnet （YAG：Ce3＋,pr3＋） nanoparticles with good dispersity and uniform grain sizes in the range of 50-80 nm were prepared by a two-step route, which consisted of a modified co-precipitation preparation of mixed metal hydroxide hydrate intermediates at low temperature of about 40℃ and a subsequent calcination conversion of the synthesized intermediates to crystalline nanoparticle products at about 1000℃. The influences of both the lanthanide ion （Ce3＋ and Pr3＋） doping concentration and different doping （Ce3＋/pr3＋） ratio on the photoluminescence intensity were systematically investigated. The synthesized （Ce0.6Pr0.4）0.04Y2.96Al5O12 nanoparticles were near spherical nanoclusters with good dispersity and uniform sizes in the range of 50-80 nm for about 85% of the particles. The strongest photoluminescence intensity was observed for the （Ce0.6Pr0.4）0.04Y2.96Al5O12 nanoparticle products.

Optical simulation of phosphor layer of white LEDs

A Matlab （2009a） program was developed to simulate the photons emitted by the LED chips. The photons＇ transmission, reflection, and refraction in phosphor layers with different shapes were calculated in this program. The CCT was calculated at different emergent angles with different layer profiles, such as planar layer, hemispherical layer （with different diameters）, half ellipsoid layer and other irregular shapes. As a consequence of optimization of angular color uniformity, the trend of configuration of the phosphor layer was discussed and analyzed.