Advanced Materials Research Vols. 399-401

Abstract: Sapphire single crystal is widely used in a variety of modern applications from GaN-based LED to military optical systems because of its excellent combination of optical, mechanical, thermal and chemical properties. The dislocations affecting the quality of sapphire crystal were studied by chemical etching and optical microscopy in this paper. The experimental results showed that the dislocation corrosion pits of (11-20) plane in sapphire crystals grown by Kyropoulos method is diamond-shaped and (1-102) plane is isosceles triangle and the density of dislocations in samples grown by Czochralski method is about two orders of magnitude higher than that in samples grown by Vertical Bridgman method. The formation mechanism of defects and proposes was also discussed.

Abstract: Fe-doped Pb_0.3Sr_0.7TiO₃ (PST) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates with sol–gel method. The structure and surface morphology of Fe-doped PST thin films were investigated as a function of Fe concentration by x-ray diffraction (XRD) and atomic force microscopy (AFM). The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1M Hz at room temperature. It’s found that the dielectric constant, dielectric loss and tunability of Fe-doped PST films decreased with the increase of Fe content. The effects of Fe doping on the microstructure, dielectric and tunable properties of thin films were analyzed. Though the undoped PST thin film exhibited the highest dielectric constant of 2011 and the largest tunability of 76%, the 6 mol% Fe doped PST thin films had the highest figure of merit (FOM) of 17.9 for its lowest dielectric loss.

Abstract: Seven europium complexes of 2-pyrazinecarboxylate (pyca) doped with inert fluorescent lanthanide ions (La³⁺, Y³⁺) have been synthesized. Elemental analysis, IR spectroscopy, absorption spectroscopy and TG-DSC analysis showed that the complexes have the formulas of Eu(pyca)₃•3H₂O and Eu_xRE_1-x(pyca)₃•3H₂O (RE=La, Y; x = 0.7,0.5,0.3), respectively. The lanthanide ions coordinated with carboxylic oxygen atoms and nitrogen atoms of pyca. Luminescence spectra and luminescence life-times of the complexes have been measured and their quantum yields were calculated. The results showed that the existence of La³⁺ and Y³⁺ ions could enhance the luminescence intensity and quantum yield of the europium complexes, which may arise from the intramolecular energy transfer between the inert fluorescent lanthanide ions and Eu³⁺ ion. Those doped complexes have the advantages of strong luminescence, low cost and practical application value.

Abstract: The Sm³⁺-Doped La₂O₃ powders were prepared by precipitation method. The room temperature photoluminescence (PL) spectra of Sm³⁺-Doped La₂O₃ powders doped with different Sm³⁺ concentration excited at 405 nm have been investigated. The PL spectra showed three main strong emissions peaks at near 572, 613, and 657 nm, which were due to the f-f forbidden transitions of the 4f electrons of Sm³⁺, corresponding to ⁴G_5/2→⁶H_5/2 (572 nm), ⁶H_7/2(613 nm), and ⁶H_9/2(657 nm), respectively. The optimum Sm³⁺ concentration in La₂O₃ powders for optical emission was determined to be 2.0 %. Since the 2% Sm-doped La2O3 offer a rather strong f–f transition excitation in near the UV region, the as-prepared phosphors are likely to be used as potential red phosphors for near-ultraviolet (370-410 nm) light-emitting diodes (LEDs).

Abstract: The electrochemical deposition of thiophene and CdSe on TiO₂/ITO by cyclic voltammetry(CV) technique was carried out to study the influence of conditions on the preparation and photophysical performance of poly(thiophene) (PTh)/CdSe double layers electrode. The chemical structure of the obtained polymer was characterized by FT-IR, Raman, X-ray diffraction, UV-vis spectroscopy. The morphology was observed by electronic scanning microscope (SEM) which showed nano-grain shape. Finally the photovoltaic performance of the solar cell which was composed of PTh/CdSe/TiO2 composite film used as working electrode, Pt used as counter electrode was investigated. And mechanism of photogenerated electron of PTh/CdSe electrode was proposed. The results showed that TiO₂ electrode modified by PTh/CdSe composite film had good response on irradiation, which indicated the PTh/CdSe was promising dye in solar cell.

Abstract: A series of orange-red phosphors M₂P₂O₇: Eu³⁺ (M = Ca, Sr, Ba ) were prepared by traditional solid-state reaction method. X-ray diffraction analysis confirmed the formation of Ca₂P₂O₇, Sr₂P₂O₇ and Ba₂P₂O₇. Scanning electron-microscopy observation indicated a narrow size-distribution of about 0.6~1 μm for the particles with a quadrate shape. Photoluminescence spectra of M₂P₂O₇(M = Ca, Sr, Ba ): Eu³⁺ phosphors showed a strong excitation peak around 393 nm, and Ca₂P₂O₇: Eu³⁺, Sr₂P₂O₇: Eu³⁺ and Ba₂P₂O₇: Eu³⁺ phosphors showed strong emission bands peaking at about 593 nm, which suggests that the Eu3+ ion is occupy the site with center of symmetry.

Abstract: The visible and near infrared emission spectra of Er³⁺/Tm³⁺-doped Ga₂O₃-Bi₂O₃-PbO-GeO₂ (GBPG) glasses excited at 808 nm are experimentally investigated. The results reveal that 1.53 µm emission were enhanced with an increase of Er³⁺ concentration. Furthermore, the incorporation of Er³⁺ into Tm³⁺-doped systems has also resulted in intense 522, 545 and 693nm upconversion emission intensity and an weak 660 nm red emission. The possible mechanism and related discussions on this phenomenon have been presented. The results show that Er³⁺/Tm³⁺-codoped GBPG glass may be a promising materials for developing laser and fiber optical devices.

Abstract: One solid coordination compound of Gadolinium chloride with N-acetyl-DL-alanine (C₅H₉NO₃, Ac-Ala) and imidazole(C₃H₄N₂,Im) has been prepared in absolute alcohol. The general formula Gd(C₅H₈NO₃)₂(C₃H₅N₂)₂Cl₃•3H₂O of these compounds was identified using the methods such as chemical and elemental analysis, FTIR spectra and UV spectra. The process of thermal decomposition was studied by TG-DTG. Room temperature fluorescence and phosphorescence measurement showed that the compound has good fluorescence and phosphorescence properties.

Abstract: The influence of Al doping on the magnetic properties and magnetic entropy changes (ΔS_M) of the La_0.8-xAl_xCe_0.2Fe_11.4Si_1.6 (x = 0-0.2) compounds have been investigated around their Curie temperature T_C. The incorporation of Al atoms is unfavorable for the formation of the NaZn₁₃-type phase, however, it increases the T_C by ~40 K, effectively decreases the magnetic hysteresis loss, and broadens the ΔS_M-T curve at expense of the (ΔS_M)_max of the compounds. It is also revealed that Al doping content of x = 0.06 is an important composition knee point where the doped Al start to occupy the site of Rare-earth elements, leading to a turning point for the lattice constant, T_C, and magnetic transition type.

Abstract: Spectroscopic properties in Er³⁺-doped Ga₂O₃-GeO₂-Bi₂O₃-PbO（BP）glass have been investigated and their promising application as Er³⁺-doped fiber amplifiers (EDFA) has also been evaluated under the excitation of 980 nm. The important roles of Bi₂O₃ substitution for PbO on spectroscopic properties, such as Judd-Ofelt intensity parameters (t=2, 4, 6) and emission spectra of Er³⁺, have been studied. The calculated peak emission cross-section of the 4I13/2→4I15/2 transition of Er³⁺ ions are 16.03×10^-21 cm² when the substituted PbO content by Bi₂O₃ is about 25 mol. The product of the peak emission cross-section ( ) and the full width at half-maximum (FWHM) of the sample is~689.29×10^-28 cm³, which is higher than that of Er³⁺-doped silicate, phosphate and ZBLAN glasses. It was found that the substitution of Bi₂O₃ for PbO provides two potentials: broadening the full width at half-maximum of 1.53 μm fluorescence and improving the values of FWHM× of Er³⁺. The results strongly support that the Er³⁺-doped BP2 glass could be identified as a promising material for achieving 1.53 μm fiber amplifier.