Study on the perfection of in situ P-injection synthesis LEC-InP single crystals

Undoped, S-doped and Fe-doped InP crystals with diameter up to 4-inch have been pulled in drop 10 0 drop -direction under P-rich condition by a rapid P-injection in situ synthesis liquid encapsulated Czochralski (LEC) method. High speed photoluminescence mapping, etch-pit density (EPD) mapping and scanning electron microscopy have been used to characterize the samples of the single crystal ingots. Dislocations and electrical homogeneity of these samples are investigated and compared. By controlling the thermal field and the solid-liquid interface shape, 4-inch low-EPD InP single crystals have been successfully grown by the rapid P-injection synthesis LEC method. The EPD across the wafer of the ingots is less than 5 x 10(4) cm(-2). Cluster defects with a pore center are observed in the P-rich LEC grown InP ingots. These defects are distributed irregularly on a wafer and are surrounded by a high concentration of dislocations. The uniformity of the PL intensity across the wafer is influenced by these defects. (C) 2004 Elsevier B.V. All rights reserved.

Comparison of space- and ground-grown Ce: Bi12SiO20 single crystals

Ce doped Bi12SiO20 single crystals were grown either on board of the Chinese Spacecraft-Shenzhou No.3 (SZ-3) or on the ground at the same conditions with the exception of microgravity. The surface morphology of crystals clearly showed significant differences between the space- and ground-grown portions. The space- and ground-grown crystals have been measured by X-ray rocking curve, Cc concentration distribution in growth direction, dislocation density, absorption spectrums. These results show that the compositional homogeneity and structural perfection of Ce doped crystal grown in space are obviously improved.

Raman-forbidden mode and oxygen ordering in Bi2Sr2-xLaxCuO6+gamma single crystals annealed in oxygen

A Raman-forbidden phonon mode at about 840 cm(-1) is observed popularly on the surface of pun and La-doped Bi2Sr2-xLaxCuO6+y (0 less than or equal to x less than or equal to 0.8) single crystals annealed in oxygen. A remarkable excitation dependence of this additional line is found. Based on the properties of the structure of the Bi-O layer with excess oxygen atoms and the similarity in the appearance of the Raman-forbidden modes between RBa2Cu3Ox (R = Y, Nd, Gd, Pr) and Bi2Sr2-xLaxCuO6+y systems, we attribute the manifestation of this additional line to the ordering of the interstitial oxygen in the Bi-O layers. Our results provide Raman evidences for confirming that the ordering of the movable oxygen may exist universally in high-temperature superconductors.

HYDROGEN-RELATED DONOR IN SILICON-CRYSTALS GROWN IN A HYDROGEN ATMOSPHERE

Neutron transmutation doped (NTD) silicon crystals grown in a hydrogen atmosphere have been investigated by infrared absorption spectroscopy at a low temperature (10 K). An effective-mass-like donor state HD0/+ has been found at 110.8 me V below the conduction band bottom after rapid thermal annealing (RTA). The HD0/+ formation mechanism after NTD and RTA is briefly discussed, and tentatively attributed to H atoms present in the vicinity of some residual irradiation defects, like a complex of a H atom and a H-saturated vacancy.

Solvothermal synthesis and characterization of Ln (Eu3+, Tb3+) doped hydroxyapatite

Luminescent Ln (Eu3+, Tb3+) doped hydroxyapatite (Eu:HAp, Tb:HAp) phosphors were successfully fabricated via the cetyltrimethylammonium bromide (CTAB)/n-octane/n-butanol/water microemulsion-mediated solvothermal process. The structure, morphology, and optical properties were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and photoluminescence (PL) spectra as well as the kinetic decays, respectively.

Combustion synthesis and luminescent properties of the Eu3+-doped yttrium oxysulfide nanocrystalline

Nanocrystallinc Y2O2S:Eu3+ was successfully prepared with a combustion synthesis method, the corresponding bulk Y2O2S:Eu3+ was synthesized by conventional sulfur flux method. The results of XRD indicated that both bulk and nanocrystalline Y2O2S:Eu3+ have Pure hexagonal phases. The crystallite size was calculated to be about 20 nm according to Scherrer formula, which was consistent with the size as indicated by transmission electron microscopy (TEM).

Erbium-Complex-Doped Near-Infrared Luminescent and Magnetic

A near-infrared luminescent macroporous material (PL-Macromaterial) and a near-infrared luminescent/magnetic bifunctional macroporous material (MML-Macromaterial) were synthesized by using polystyrene microspheres (PS) and Fe3O4 @polystyrene core-shell nanoparticles (Fe3O4@PS), respectively, as templates. Both the PL-Macromaterial and the M/PL-Macromaterial show the characteristic emission of the Er 3, ion. Moreover, the M/PL-Macromaterial possesses superparamagnetic properties at room temperature.

Hydrothermal Synthesis and Luminescence of Eu-Doped Ba0.92Y2.15F8.29 Submicrospheres

The nonstoichimetric Ba0.92Y2.15F8.29 submicrospheres that piled up by nanoparticles have been prepared via a solution-based method in a hydrothermal environment. The size distribution of the submicrospheres could be tuned by varying the amount of BaCl2. The fluoride source NaBF4 plays an important role in the formation of the submicrospheres. The chelator ethylenediaminetetraacetic acid regulates the growth of the primary nanoparticles as well as the aggregated submicrospheres. The photoluminescence properties of different concentrations of Eu3+-doped Ba0.92Y2.15F8.29 were investigated and the results revealed that the 8% concentration of Eu3+ ions is the optimum doping concentration and the Y3+ ions occupy the site of inversion symmetry.

Highly uniform and monodisperse beta-NaYF4 : Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprism crystals: Hydrothermal synthesis and luminescent properties

beta-NaYF4:Ln(3+) (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb3+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu(3+) (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to D-5(0-3) -> F-7(J) (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively.

Investigation on relationship between charge transfer position and dielectric definition of average energy gap in Eu3+-doped compounds

The dielectric definition of average energy gap E-g of the chemical bond has been calculated quantitatively in Eu3+-doped 30 lanthanide compounds based on the dielectric theory of chemical bond for complex structure crystals. The relationship between the experimental charge transfer (CT) energy of Eu3+ and the corresponding average energy gap E-g has been studied. The results show that the CT energy increases linearly with increasing of the average energy gap E-g. The linear model is obtained. It allows us to predict the CT position of Eu3+-doped lanthanide compounds with knowledge of the crystal structure and index of refraction. Applied to the Ca4GdO(BO3)(3):Eu and Li2Lu5O4(BO3)(3):Eu crystals, the predicted results of CT energies are in good agreement with the experimental values, and it can be concluded that the lowest CT energy in Li2Lu5O4(BO3)(3):Eu originates from the site of Lu1.

Sol-ogel deposition and luminescence properties of lanthanide ion-doped Y2(1-x)Gd2xSiWO8 (0 <= x <= 1) phosphor films

Y2(1-x) Gd2xSiWO8 : A ( 0 <= x <= 1; A= Eu3+, Dy3+, Sm3+, Er3+) phosphor films have been prepared on silica glass substrates through the sol - gel dip-coating process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), atomic force microscope (AFM), scanning electron microscopy (SEM) and photoluminescence spectra as well as lifetimes were used to characterize the resulting films. The results of the XRD indicated that the films began to crystallize at 800 degrees C and crystallized completely at 1000 degrees C. The AFM and SEM study revealed that the phosphor films, which mainly consisted of closely packed grains with an average size of 90 - 120 nm with a thickness of 660 nm, were uniform and crack free. Owing to an efficient energy transfer from the WO42- groups to the activators, the doped lanthanide ion ( A) showed its characteristic f - f transition emissions in crystalline Y2(1-x) Gd2xSiWO8 (0 <= x <= 1) films. The optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 21, 5, 3 and 7 mol% of Y3+ in Y2SiWO8 films, respectively.

Synthesis and spectral properties of lutetium-doped CeF3 nanoparticles

CeF3 and lutetium-doped CeF3 nanoparticles with the dopant concentration of 17, 25, 30, 42 and 50 mol% (molar ratio, Lu/Ce) were synthesized. XRD patterns were indexed to a pure CeF3 hexagonal phase even under the dopant concentration of 50 mol%. Environmental scanning electron microscopy-field emission gun (ESEM-FEG) was used to characterize the morphology of the final products. From the luminescence spectra of the products, we can get a broad emission ranging from 290 to 400 nm with peak at 325 nm. Lutetium-doping increases the luminescence intensity. We got. the most intense luminescence at the dopant concentration of 30 mol%.

Dependence of charge transfer energy on crystal structure and composition in Eu3+-doped compounds

We report a method for estimating the positions of charge transfer (CT) bands in Eu3+-doped complex crystals. The environmental factor ( he) influencing the CT energy is presented. he consists of four chemical bond parameters: the covalency, the bond volume polarization, the presented charge of the ligand in the chemical bond, and the coordination number of the central ion. These parameters are calculated with the dielectric theory of complex crystals. The relationship between the experimental CT energies and calculated environmental factors was established by an empirical formula. The calculated values are in good agreement with the experimental results. Such a relationship was confirmed by detailed analysis. In addition, our method is also useful to predict the charge-transfer position of any other rare earth ion.

Dy3+- and Eu3+-doped LaGaO3 nanocrystalline phosphors for field emission displays

Nanocyrstalline LaGaO3 and Dy3+- and Eu3+-doped LaGaO3 were prepared through a Pechini-type sol-gel process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), photoluminescence, cathodoluminescence spectra, and lifetimes were utilized to characterize the samples. XRD reveals that the samples begin to crystallize at 900 degrees C and pure LaGaO3 phase can be obtained at 1000 degrees C. FE-SEM images indicate that the Dy3+- and Eu3+-doped LaGaO3 samples are both composed of aggregated spherical particles with sizes ranging from 40 to 80 nm. Under the excitation of ultraviolet light and low voltage electron beams (1-5 kV), the undoped LaGaO3 sample shows a strong blue emission peaking at 433 nm, and the Dy3+- and Eu3+-doped LaGaO3 samples show their characteristic emissions of Dy3+ (F-4(9/2)-H-6(15/2) and F-4(9/2)-H-6(13/2) transitions) and Eu3+ (D-5(0,1,2)-F-7(1,2,3,4) transitions), respectively. The relevant luminescence mechanisms are discussed.

Preparation and optical properties of trivalent europium-doped bulk and nanocrystalline SrY2O4

The nanocrystalline Sry(2)O(4):Eu3+ was prepared by a poly(vinyl alcohol) (PVA)+glycine-assist combustion method. The results of x-ray diffraction indicate that the resulting Sry(2)O(4):Eu3+ nanocrystals have much broader and less intense peaks compared with those in bulk material. The charge-transfer bands in Sry(2)O(4):Eu3+ nanocrystals shift to higher energies in contrast to those in bulk material. The spectral results revealed that in bulk SrY2O4: Eu3+ the Eu3+ ions occupied three nonequivalent sites, with one at the Sr site: one at the Y(1) site and another at the Y(2) site, while in nanocrystalline SrY2O4: Eu3+, the Eu3+ ions occupied only two nonequivalent sites; one at the Y(1) site and the other at the Y(2) site. Finally, by theoretical calculation and analysis, the analyzed results are in reasonable agreement with our experimental results.