红外飞秒激光诱导Ce^3＋掺杂闪烁晶体的上转换发光研究

本文研究了红外飞秒激光照射下Ce^3＋ 掺杂的YAP和LSO两种闪烁晶体的上转换发光现象.实验发现在飞秒激光泵浦下,这两种晶体的荧光均来自于Ce^3＋离子的5d-4f跃迁.荧光强度与泵浦光功率之间的依赖关系揭示了Ce^3＋：YAP和Ce^3＋：LSO晶体的上转换过程皆由三光子吸收过程所主导.分析表明,Ce^3＋：YAP和Ce^3＋：LSO晶体中的三光子吸收是三光子同时吸收.

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.

Judd-Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the TM3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Omega(2)=9.3155 x 10(-20) cm(2), Omega(4)=8.4103 x 10(-20) cm(2), Omega(6)=1.5908 x 10(-20) cm(2), the fluorescence lifetime is calculated to be 2.03 ms for F-3(4) -> H-3(6) transition, and the integrated emission cross section is 5.81 x 10(-18) cm(2). Room-temperature laser action near 2 mu m under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuous-wave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06 mu m with spectral bandwidth of similar to 13.6 nm.

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)

Structure and UV emission of nanocrystal ZnO films by thermal oxidation of ZnS films

ZnO films prepared by the thermal oxidation of the ZnS films through thermal evaporation are reported. The as-deposited ZnS films have transformed to ZnO films completely at 400 degrees C. The 400-700 degrees C annealed films with a preferential c-axis (002) orientation have a hexagonal wurtzite structure. The band gap of ZnO films shifts towards longer wavelength with the increase of the annealing temperature. The relationship between the band gap energy of ZnO films and the grain size is discussed. The shift of the band gap energy can be ascribed to the quantum confinement effect in nanocrystal ZnO films. The photoluminescence spectra of ZnO films show a dominant ultraviolet emission and no deep level or trap state defect emission in the green region. It confirms the absence of interstitial zinc or oxygen vacancies in ZnO films. These results indicate that ZnO film prepared by this simple thermal oxidation method is a promising candidate for optoelectronic devices and UV laser. (c) 2005 Elsevier BN. All rights reserved.

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.

退火对电子束热蒸发Al2O3薄膜性能影响的实验研究

用电子束热蒸发方法镀制了Al2O3材料的单层膜，对它们在空气中进行了250～400℃的高温退火。对样品的透射率光谱曲线进行了测量，计算了样品的消光系数、折射率和截止波长。通过X射线衍射仪(XRD)测量分析了薄膜的微观结构，采用表面轮廓仪测量了样品的表面均方根粗糙度。结果发现随着退火温度的提高光学损耗下降，薄膜结构在退火温度为400℃时仍然为无定形态，样品的表面粗糙度随退火温度的升高而增加。引起光学损耗下降起主导作用的是吸收而不是散射，吸收损耗的下降主要是由于退火使材料吸收空气中的氧而进一步氧化，从而使薄膜

High-performance 4H-SiC based metal-semiconductor-metal ultraviolet photodetectors with Al2O3 SiO2 films

4H-silicon carbide (SiC) metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors with Al2O3/SiO2 (A/S) films employed as antireflection/passivation layers have been demonstrated. The devices showed a peak responsivity of 0.12 A/W at 290 nm and maximum external quantum efficiency of 50% at 280 nm under 20 V electrical bias, which were much larger than conventional MSM detectors. The redshift of peak responsivity and response restriction effect were found and analyzed. The A/S/4H-SiC MSM photodetectors were also shown to possess outstanding features including high UV to visible rejection ratio, large photocurrent, etc. These results demonstrate A/S/4H-SiC photodetectors as a promising candidate for OEIC applications. (C) 2008 American Institute of Physics.

Annealing effects on the optical and structural properties of Al2O3/SiO2 films as UV antireflection coatings on 4H-SiC substrates

Al2O3/SiO2 films have been prepared by electron-beam evaporation as ultraviolet (UV) antireflection coatings on 4H-SiC substrates and annealed at different temperatures. The films were characterized by reflection spectra, ellipsometer system, atomic force microscopy (AFM), X-ray diffraction (XRD) and Xray photoelectron spectroscopy (XPS), respectively. As the annealing temperature increased, the minimum reflectance of the films moved to the shorter wavelength for the variation of refractive indices and the reduction of film thicknesses. The surface grains appeared to get larger in size and the root mean square (RMS) roughness of the annealed films increased with the annealing temperature but was less than that of the as-deposited. The Al2O3/SiO2 films maintained amorphous in microstructure with the increase of the temperature. Meanwhile, the transition and diffusion in film component were found in XPS measurement. These results provided the important references for Al2O3/SiO2 films annealed at reasonable temperatures and prepared as fine anti-reflection coatings on 4H-SiC-based UV optoelectronic devices. (c) 2008 Elsevier B.V. All rights reserved.

Measurements of total scattering spectra from bocaccio (Sebastes paucispinis)

Marine sportfishing in southern California is a huge industry with annual revenues totaling many billions of dollars. However, the stocks of lingcod and six rockfish species have been declared overfished by the Pacific Fisheries Management Council. As part of a multifaceted fisheries management plan, marine conservation areas, covering many million square nautical miles, have been mandated. To monitor the recovery of the rockfish stocks in these areas, scientists are faced with the following challenges: 1) multiple species of rockfish exist in these areas; 2) the species reside near or on the bottom at depths of 80 to 300 m; and 3) they are low in numerical density. To meet these challenges, multifrequency echosounders, multibeam sonar, and cameras mounted on remotely operated vehicles are frequently used (Reynolds et al., 2001). The accuracy and precision of these echosounder results are largely dependent upon the accuracy of the species classification and target strength estimation (MacLennan and Simmonds, 1992).

Comparison of the Transcriptional Profiles of Melanocytes from Dark and Light Skinned Individuals under Basal Conditions and Following Ultraviolet-B Irradiation

We analysed the whole-genome transcriptional profile of 6 cell lines of dark melanocytes (DM) and 6 of light melanocytes (LM) at basal conditions and after ultraviolet-B (UVB) radiation at different time points to investigate the mechanisms by which melanocytes protect human skin from the damaging effects of UVB. Further, we assessed the effect of different keratinocyte-conditioned media (KCM+ and KCM-) on melanocytes. Our results suggest that an interaction between ribosomal proteins and the P53 signaling pathway may occur in response to UVB in both DM and LM. We also observed that DM and LM show differentially expressed genes after irradiation, in particular at the first 6h after UVB. These are mainly associated with inflammatory reactions, cell survival or melanoma. Furthermore, the culture with KCM+ compared with KCM- had a noticeable effect on LM. This effect includes the activation of various signaling pathways such as the mTOR pathway, involved in the regulation of cell metabolism, growth, proliferation and survival. Finally, the comparison of the transcriptional profiles between LM and DM under basal conditions, and the application of natural selection tests in human populations allowed us to support the significant evolutionary role of MIF and ATP6V0B in the pigmentary phenotype.

Theoretical and experimental absorption spectra study of [(FeTPPbipy]·)n provided by TD-DFT calculations

Comunicación a congreso (póster): 11th European Biological Inorganic Chemistry Conference EUROBIC 11. 12-16 September, 2012 - Granada (Spain)