Effects of annealing on the color, absorption spectra, and light yield of Ce : YAlO3 single crystal grown by the temperature gradient technique

YAlO3 single crystal doped with Ce3+ at concentration 1% was grown by the temperature gradient technique. The as-grown crystal was pink. After H-2 annealing or air annealing at 1400degreesC for 20 h, the crystal was turned into colorless. We concluded there were two kinds of color centers in the as-grown crystal. One is F+ center attributed to absorption band peaking at about 530 nm, the other is O- center attributed to absorption band peaking at about 390 nm. This color centers model can be applied in explaining the experiment phenomena including the color changes, the absorption spectra changes, and the light yield changes of Ce:YAP crystals before and after annealing. (C) 2004 American Institute of Physics.

Cr4+在八面体格位中的光谱特性研究

Cr-doped and Mg, Cr-codoped Al2O3 crystals were grown by Czochralski method. The latter has a broad absorption peak in 900-1600nm region. We investigated the change of the absorption band with annealing under different atmospheres or temperatures. Through establishing a structure defect model, we successfully interpreted all the experiment results and confirmed that the extremely broad infrared absorption band belonged to Cr4+, which should occupy the octahedral sites in Al2O3.

Anomalous scattering factor determined by semicircle fitting near the K-absorption edge of Ge

It is shown that the locus of the f' + if '' plot in the complex plane, f' being determined from measured f '' by using the dispersion relation, looks like a semicircle very near the absorption edge of Ge. The semicircular locus is derived from a quantum theory of X-ray resonant scattering when there is a sharp isolated peak in f '' just above the K-absorption edge. Using the semicircular behavior, an approach is proposed to determine the anomalous scattering factors in a crystal by fitting known calculated values based on an isolated-atom model to a semicircular focus. The determined anomalous scattering factors f' show excellent agreement with the measured values just below the absorption edge. In addition, the phase determination of a crystal structure factor has been considered by using the semicircular behavior.

Nanosecond nonlinear absorption in Au and Ag nanoparticles precipitated glasses induced by a femtosecond laser

We obtain Au and Ag nanoparticles precipitated in glasses by irradiation of focused femtosecond pulses, and investigate the nonlinear absorptions of the glasses by using Z-scan technique with ns pulses at 532 nm. We observe the saturable absorption behavior for An nanoparticles precipitated glasses and the reverse saturable ones for Ag ones. We also obtain, by fitting to the experimental results in the light of the local field effect near and away from the surface plasmon resonance, chi(m)((3)) = 4.5 x 10(-7) and 5.9 x 10(-8) esu for m the imaginary parts of the third-order susceptibilities for Au and Ag nanoparticles, respectively. The nonlinear response of Au nanoparticles in the glass samples arises mainly from the hot-electron contribution and the saturation of the interband transitions near the surface plasmon resonance, whereas that of Ag nanoparticles in the glass samples from the interband transitions. These show that the obtained glasses can be used as optoelectronic devices suiting for different demands. (c) 2005 Elsevier B.V. All rights reserved.

First-principles study of the electronic structures and absorption spectra for the PbMoO4 crystal with lead vacancy

The electronic structures and absorption spectra for the perfect PbMoO4 crystal and the crystal containing lead vacancy V-Pb(2-) with lattice structure optimized are calculated using density functional theory code CASTEP. The calculated absorption spectra of the PbMoO4 crystal containing V-Pb(2-) exhibit three absorption bands peaking at 2.0 eV (620 nm), 3.0 eV (413 run) and 3.3 eV (375 nm), which are in good agreement with experimental values. The theory predicts that the 390 nm, 430 nm and 580 run absorption bands are related to the existence of V-Pb(2-) in the PbMoO4 crystal.

First-principles calculations of electronic structures and absorption spectra of YAlO3 crystals with F center

National Nature Science Foundation of China (Grant No. 60607015)

Role of interface absorption in laser-induced local heating of optical coatings

Considering the interface absorption in optical coatings, we propose a model to simulate interface absorption. Calculations are made and the temperature field of several kinds of thin film multilayers, including those of partial reflectivity, high-reflectivity, and antireflectivity coatings are analyzed. The interface absorption is found to greatly influence the temperature distribution within multilayer coatings and to weaken the laser damage resistance of the samples. The real-time results of the photothermal deflection technique for laser induced damage to samples supports the model. (C) 1997 Society of Photo-Optical Instrumentation Engineers.

Enhancement of near-band-edge photoluminescence of ZnO thin films in sandwich configuration at room temperature

ZnO/ITO/ZnO sandwich structure films were fabricated. The effects of buffer layer on the structure and optical properties of ZnO films were investigated by x-ray diffraction (XRD), photoluminescence, optical transmittance, and absorption measurements. XRD spectra indicate that a buffer layer has the effects of lowering the grain orientation of ZnO films and increasing the residual stresses in the films. The near-band-edge emissions of ZnO films deposited on both single indium tin oxide (ITO) buffer and ITO/ZnO double buffers are significantly enhanced compared with that deposited on a bare substrate due to the quantum confinement effect. (C) 2006 American Institute of Physics.

The effects of oxygen partial pressure on the optical absorption edge and the UV emission energy of ZnO films

The optical absorption edge and ultraviolet (UV) emission energy of ZnO films deposited by direct current (DC) reactive magnetron sputtering at room temperature have been investigated. With the oxygen ratio increasing, the structure of films changes from zinc and zinc oxide coexisting phase to single-phase ZnO and finally to the highly (002) orientation. Both the grain size and the stress of ZnO film vary with the oxygen partial pressure. Upon increasing the oxygen partial pressure in the growing ambient, the visible emission in the room-temperature photoluminescence spectra was suppressed without sacrificing the band-edge emission intensity in the ultraviolet region. The peaks of photoluminescence spectra were located at 3.06---3.15 eV. From optical transmittance spectra of ZnO films, the optical band gap edge was observed to shift towards shorter wavelength with the increase of oxygen partial pressure.

Development in laser induced extrinsic absorption damage mechanism of dielectric films

Absorption of host and the temperature-dependence of absorption coefficient have been considered in evaluating temperatures distribution in films, when laser pulse irradiates on films. Absorption of dielectric materials experience three stages with the increase of temperature: multi-photon absorption; single photon absorption; metallic absorption. These different absorption mechanisms correspond to different band gap energies of materials, which will decrease when the temperature of materials increases. evaluating results indicate that absorption of host increases rapidly when the laser pulse will be over. If absorption of host and the temperature-dependence of absorption are considered, the material temperatures in films will be increased by a factor of four.

Temperature fields of 355 nm HR coatings based on the interface absorption model

Temperature fields of 355 nm high-reflectance (HR) coatings were investigated based on the interface absorption model. It was found that the highest temperature in the HR coatings increased with an increase in the extinction coefficient of the interface A, B, C, Al2O3 and MgF2. The highest temperature of HR coatings that can be reached increased quickly with the increase in the extinction coefficient of interface A in particular. The temperature rises of 355 nm HR coatings at different layers and different deposition temperatures were investigated based on experiments also. The damage mechanism of 355 nm HR coatings was confirmed with temperature fields and the interface absorption model.