Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of gamma-LiAlO2

gamma-LiAlO2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 degrees C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190-1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398x10(-6)/degrees C to 16.5240x10(-6)/degrees C, and that for c axis drops from 10.7664x10(-6)/degrees C to 10.0786x10(-6)/degrees C.

Nano-modification inside transparent materials by femtosecond laser single beam

Periodic nanostructures along the polarization direction of light are observed inside silica glasses and tellurium dioxide single crystal after irradiation by a focused single femtosecond laser beam. Backscattering electron images of the irradiated spot inside silica glass reveal a periodic structure of stripe-like regions of similar to 20 nm width with a low oxygen concentration. In the case of the tellurium dioxide single crystal, secondary electron images within the focal spot show the formation of a periodic structure of voids with 30 nm width. Oxygen defects in a silica glass and voids in a tellurium dioxide single crystal are aligned perpendicular to the laser polarization direction. These are the smallest nanostructures below the diffraction limit of light, which are formed inside transparent materials. The phenomenon is interpreted in terms of interference between the incident light field and the electric field of electron plasma wave generated in the bulk of material.

High quantum fluorescence yield of Er3+ at 1.5 mu m in an Yb3+, Ce3+-codoped CaF2 crystal

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 mu m region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 -> I-4(13/2) transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+ 4I11/2 level. The quaternary-doped CaF2, system shows great potential to achieve high laser performance in the 1.5 mu m region. (c) 2006 Elsevier B.V. All rights reserved.

Growth, etching morphology and spectra of LiAlO2 crystal

gamma-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0 x 10(3) cm(-2). The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Growth and spectral properties of Er:Gd2SiO5 crystal

Er3+ -doped Gd2SiO5 (Er:GSO) single crystal with dimensions of circle divide 35 x 40 mm(3) has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd-Ofelt theory, and the intensity parameters Omega(2), Omega(4) and Omega 6 are obtained to be 6.168 x 10(-20), 1.878 x 10(-20), and 1.255 x 10(-20) cm(2), respectively. The emission cross-section has been calculated by Fuechtbauer-Ladenbury formula. (c) 2007 Elsevier B.V. All rights reserved.

Growth of highly sensitive thermoluminescent crystal alpha-Al2O3 : C by the temperature gradient technique

In this work, an alpha-Al2O3:C crystal with highly sensitive thermoluminescence was directly grown by the temperature gradient technique (TGT) using Al2O3 and graphite powders as raw materials. The optical and luminescent properties and the dosimetric characteristics of the crystal were investigated. An as-grown alpha-Al2O3:C crystal shows a single glow peak at 462 K and a blue emission peak at 415 nm. The thermoluminescence (TL) response of the crystal shows a linear-sublinear-saturation characteristic. In the dose range from 5 x 10(-6) to 10Gy, the alpha-Al2O3:C crystal shows excellent linearity, and saturation was observed at about 30Gy. The sensitivity of the crystal decreases as the heating rate increases. (c) 2008 Elsevier B.V. All rights reserved.

Spectral investigation of Yb-doped calcium pyroniobate crystal

Ytterbium-doped calcium pyroniobate single crystal has been grown for the first time. Spectral properties of Yb: Ca2Nb2O7 were investigated by emission and absorption spectra. Its cooperative luminescence and fluorescence lifetime were also studied. Yb ions in Ca2Nb2O7 showed very broad absorption and emission bandwidth and relatively large absorption and emission cross-sections. Along with other optical properties, this Yb-doped crystal would be a potential self-frequency doubling femtosecond laser gain material. (C) 2007 Published by Elsevier B.V.

Polarized spectral analysis of Ho3+ ions in biaxial YAlO3 crystal for 2 mu m lasers

An Ho3+-doped YAlO3 (Ho : YAP) single crystal has been grown by the Czochralski technique. The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of the crystal are measured at room temperature. The spectroscopic parameters are calculated based on Judd-Ofelt theory, and the effective phenomenological intensity parameters Omega(2,eff), Omega(4,eff) and Omega(6,eff) are obtained to be 2.89 x 10(-20), 2.92 x 10(-20) and 1.32 x 10(-20) cm(2), respectively. The room-temperature fluorescence lifetime of the Ho3+ 5I(7) -> I-5(8) transition is measured to be 8.1 ms. Values of the absorption and emission cross-sections with different polarizations are presented for the I-5(7) manifold, and the polarized gain cross-section curves are also provided and discussed.

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.

1ps passively mode-locked laser operation of Na, Yb : CaF2 crystal

Diode-pumped passively mode-locked laser operation of Yb3+,Na+:CaF2 single crystal has been demonstrated for the first time. By using a SESAM ( semiconductor saturable mirror), simultaneous transform-limited 1-ps passively mode-locked pulses, with the repetition rate of 183MHz, were obtained under the self-Q-switched envelope induced by the laser medium. The average output power of 360mW was attained at 1047nm for 3.34W of absorbed power at 976nm, and the corresponding pulse peak power arrived at 27kW, indicating the promising application of Yb3+,Na+-codoped CaF2 crystals in achieving ultra-short pulses and high pulse peak power. (c) 2005 Optical Society of America.

Properties of GaAs single crystals grown by molecular beam epitaxy at low temperatures

Properties of GaAs single crystals grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) have been studied. The results shaw that excessive arsenic atoms of about 10(20) cm(-3) exist in LTMBE GaAs in the form of arsenic interstitial couples, and cause the dilation in lattice parameter of LTMBE GaAs, The arsenic interstitial couples will be decomposed, and the excessive arsenic atoms will precipitate during the annealing above 300 degrees C. Arsenic precipitates accumulate in the junctions of epilayers with the increase in the temperature of annealing. The depletion regions caused by arsenic precipitates overlap each other in LTMBE GaAs, taking on the character of high resistivity, and the effects of backgating or sidegating are effectively restrained.

Wet etching and infrared absorption of AlN bulk single crystals

The defects and the lattice perfection of an AlN (0001) single crystal grown by the physical vapor transport (PVT) method were investigated by wet etching, X-ray diffraction (XRD), and infrared absorption, respectively. A regular hexagonal etch pit density (EPD) of about 4000 cm~(-2) is observed on the (0001) A1 surface of an AlN single crystal. The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process. The XRD full width at half maximum (FWHM) of the single crystal is 35 arcsec, suggesting a good lattice perfection. Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm~(-1), respectively. These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.

Characterization of Phosphorus Diffused ZnO Bulk Single Crystals

Phosphorus was diffused into CVT grown undoped ZnO bulk single crystals at 550 and 800℃ in a closed quartz tube. The P-diffused ZnO single crystals were characterized by the Hall effect, X-ray photoelectron spectroscopy （XPS）, photoluminescence spectroscopy （PL）, and Raman scattering. The P-diffused ZnO single crystals are n-type and have higher free electron concentration than undoped ZnO, especially for the sample diffused at 800℃. The PL measurement reveals defect related visible broad emissions in the range of 420-550nm in the P-diffused ZnO samples. The XPS result suggests that most of the P atoms substitute in the Zn site after they diffuse into the ZnO single crystal at 550℃ ,while the P atom seems to occupy the O site in the ZnO samples diffused at 800℃. A high concentration of shallow donor defect forms in the P-diffused ZnO,resulting in an apparent increase of free electron concentration.

Two novel molybdenum complexes containing [Mo2O2S2](2+) fragment: synthesis, crystal structures and catalytic studies

Mo2O2S2(HGly)(GlY)(2) 1 and K-6[Mo2O2S2(nta)(2)][Mo2O2S2(ntaH)(2)]center dot 4H(2)O 2 were synthesized by the reactions of (NH4)(2)MoS4 and amino acids L (L = glycine, nitrilotriacetic acid) in ethanol-water medium at ambient temperature. The two complexes were characterized by elemental analysis, infrared spectra, UV-visible spectra, TG-DTA and XPS.

Crystal packing motifs of oligothiophenes end-capped with N-containing aryls

Oligothiophenes (OThs) end-capped with 3-quinolyl or pyridyl with nitrogen atom at meta-, ortho- or para-position were synthesized. The single-crystal structures of the resulting molecules, i.e., o-PyTh4, m-PyTh4, p-PyTh4, QuTh2, and QuTh3, were successfully determined by single-crystal X-ray analysis. Pyridyl end-capped OThs; o-PyTh4, m-PyTh4, and p-PyTh4, adopt the different herringbone packing arrangement in crystals depending on the position of the nitrogen atom because of the presence of weak C-H center dot center dot center dot N hydrogen bonds. The p-PyTh4 molecules are linked each other along the long axis of the molecules to form the extended chains by C-H center dot center dot center dot N dimer synthon. For m-PyTh4, the C-H center dot center dot center dot N interactions two-dimensionally extend through C-H center dot center dot center dot N trimer synthon.