Valence state change and refractive index change induced by femtosecond laser irradiation in Sm3+ doped fluoroaluminate glass

We report femtosecond laser induced valence state and refractive index change in transparent Sin(3+)-doped fluoroaluminate glass. The effect of annealing on the induced changes was studied and the thermal stability of these changes was discussed. The results show that the femtosecond laser induced valence state change is more stable than the induced refractive index change. The observed phenomenon could be applied to design the thermally erasable or stable storage medium. (c) 2007 Elsevier B.V. All rights reserved.

Structure characteristics and valence state study for La1-xNaxTiO3 synthesized under high-pressure and high-temperature conditions

By using a novel high-pressure, high-temperature method, perovskite oxides of La1-xNaxTiO3 (x = 0.05, 0.1-0.8) with mixed valence state were synthesized. XRD analysis shows a cubic cell for the samples. Cell volumes of the samples with 0.1 less than or equal to x less than or equal to 0.5 decreases as x increases, and the cell Volume for x = 0.05 is smaller than that for x = 0.1. XPS of surface and EPR measurements indicate that Ti ions are of mixed valence of +3 and +4 and that A-cations vacancies exist in the samples. As x increases, the amount of Ti3+ ions decreases and the amount of A-cations vacancies increases. The valence state of Ti ions can be altered by changing both pressure and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

VALENCE STATE EQUILIBRIA BETWEEN COBALT AND MANGANESE IONS AND MAGNETIC-PROPERTIES OF LACO0.9MN0.1O3

According to the thermodynamic equilibria between the low spin state Co(III) (t2g6e(g)0) ion and the high spin state Co3+ (t2g4e(g)2) ion and between the cobalt and manganese ions with different valence state and spin state, an approximate semiempirical f

SPIN AND VALENCE STATE EQUILIBRIA OF COBALT AND MAGNETIC-PROPERTIES OF LACOO3

On the basis of the spin and valence state equilibria and superexchange interaction of the various cobalt ions in LaCoO3, an approximate semiempirical formula has been proposed and used to calculate magnetic susceptibilities of LaCoO3 over a wide temperature range (100-1200 K). The results indicate that there are thermodynamic equilibria between the low spin state Co(III) (t2g6e(g)0) ion, the high spin state Co3+ (t2g4e(g)2) ion, the Co(II) (t2g6e(g)1) ion and the Co(IV) (t2g5e(g)0) ion in LaCoO3. The energy difference between the low spin state Co(III) and the high spin state Co3+ is about 0.006 eV. The content of the low spin state Co(III) ion is predominant in LaCoO3 and the content of the high spin state Co3+ ion varies with temperature, reaching a maximum at about 350 K, then decreasing gradually with increasing temperature. At low temperature the contents of the Co(II) ion and the Co(IV) ion in LaCoO3 are negligible, while above 200 K the contents of both the Co(II) ion and the Co(IV) ion increase with increasing temperature; however, the content of the Co(II) ion always is larger than that of the Co(IV) ion at any temperature. These calculated results are in good agreement with experimental results of the Mossbauer effect, magnetic susceptibility and electrical conductivity of LaCoO3.

PREPARATION, STRUCTURE AND INFLUENCE OF VALENCE STATE ON LASR2-XCAXV3O9+/-Y

New compounds LaSr2-xCa-(x)V3O9+/-y (x = 0.0, 0.67, 1.0, 1.33 and 2.0) have been synthesized with a simple new method X ray powder diffraction results indicate that they are single compound. Their lattice constants are calculated. The structure of LaSr2-xCa(x)V39+/-y changed from cubic to orthorhombic and back to cubic with the increase of calcium content. The results of weight gain in TG and XPS curves show that vanadium with lower valent state is oxidized to higher valent state at higher temperature. The oxygen content of new compounds are calculated from the weight gain. It is shown that V3+ and V4+ may coexist in LaSr2-xCa(x)V3O9+/-y. These compounds show that low resistivity.

Three-dimensional micro- and nano-fabrication in transparent materials by femtosecond laser

Femtosecond pulsed lasers have been widely used for materials microprocessing. Due to their ultrashort pulse width and ultrahigh light intensity, the process is generally characterized by the nonthermal diffusion process. We observed various induced microstructures such as refractive-index-changed structures, color center defects, microvoids and microcracks in transparent materials (e.g., glasses after the femtosecond laser irradiation), and discussed the possible applications of the microstructures in the fabrication of various micro optical devices [e.g., optical waveguides, microgratings, microlenses, fiber attenuators, and three-dimensional (3D) optical memory]. In this paper, we review our recent research developments on single femtosecond-laser-induced nanostructures. We introduce the space-selective valence state manipulation of active ions, precipitation and control of metal nanoparticles and light polarization-dependent permanent nanostructures, and discuss the mechanisms and possible applications of the observed phenomena.

High-pressure and-temperature synthesis and characterization of mixed valence perovskite oxides LaTi1-xMgxO3

Perovskite oxides LaTi1-xMgxO3 (x = 0.25, 0.5) were synthesized using high-pressure and-temperature method. LaTi0.75Mg0.25O3 is a new compound. This new synthesis route has some advantages. XRD analysis showed that the x = 0.25 sample belongs to cubic perovskite-type structure and the a = 0.5 sample belongs to orthorhombic perovskite-type structure. EPR measurement indicated that Ti ions were in mixed valence state of +3 and +4. IR measurement indicated that the vibration frequency and width of BO6 octahedron stretching vibration absorption band decreases with the increasing of x. The valence state of Ti ions can be altered by high-pressure and-temperature. (C) 2000 Elsevier Science S.A. All rights reserved.

Valence stability and change of Eu(II)in oxides

Valence stability and change of Eu(II) in oxides have been studied by luminescence spect a. The results show that the valence stability and change of Eu(II)in oxides is closely related to the radius and electric charge of positive ions substituted by Eu(II) and crystal structure of the host such as Al2O3 which can form alpha-Al2O3 single phase and alpha-Al2O3 and gamma-Al2O3 mixed phases under different reaction temperatures. A, fairly good explanation is made by the proposed relation between energy coefficient and crystal structure for the first time to the observed experiment results. if the energy coefficients of substitution ions is more than that of Eu(II), the lattice substitution of Eu(II)for these ions is not occured generally and valence stare of Eu(II)is not stable and be easily changed into Eu(III). The lattice of gamma-Al2O3 can stablize the valence state of Eu(II)within certain coped concentration and in alpha-Al2O3 crystal lattice Eu(II)can be easily changed into Eu(III).

VALENCE AND MAGNETIC-PROPERTIES OF YSR2-XCAXV3O9-Y

Compounds YSr22-xCaxVO9-y have an orthorhombic symmetry. XPS results show that the vanadium ions exist in the mixing valence in the system. Temperature dependence of magnetic susceptibility represents the Curie-Weiss law. The valence state of vanadium obviously affects the magnetic properties of YSr2-xCaxV3O9-y. The system exhibits a paramagnetic behavior from 300K to 1073K.

Infrared luminescence properties of bismuth-doped barium silicate glasses

Infrared (IR) luminescence covering 1.1 to similar to 1.6 mu m wavelength region was observed from bismuth-doped barium silicate glasses, excited by a laser diode at 808 nm wavelength region, at room temperature. The peak of the IR luminescence appears at 1325 nm. A full width half-maximum (FWHM) and the lifetime of the fluorescence is more than 200 nm and 400 mu s, respectively. The fluorescence intensity increases with Al2O3 content, but decreases with BaO content. We suggest that the IR luminescence should be ascribed to the low valence state of bismuth Bi2+ or Bi+, and Al3+ ions play an indirect dispersing role for the infrared luminescent centers.

Tuning the Eu luminescence in glass materials synthesized in air by adjusting glass compositions

The doped Eu3+ ions can be partly reduced to Eu2+ in a series of MO-B2O3: Eu (M=Ba, Sr, Ca) glasses synthesized in air atmosphere, but not in the 12CaO-7Al(2)O(3): Eu glass. The different redox-behavior of Eu ions in these two glass systems is attributed to the different host optical basicity. It is found that a lower valence state of Eu2+ is more favorable in acidic glasses, which have lower optical basicities. A notion of the critical value of optical basicity is introduced empirically, which can be used as a guide for the selection of glass composition suitable to incorporate Eu2+ for luminescence. (C) 2006 Elsevier B.V. All rights reserved.

Broadband infrared luminescence from bismuth-doped GeS2-Ga2S3 chalcogenide glasses

Near-infrared luminescence is observed from bismuth-doped GeS2-Ga2S3 chalcogenide glasses excited by an 808 nm laser diode. The emission peak with a maximum at about 1260 nm is observed in 80GeS(2)-20Ga(2)S(3):0.5Bi glass and it shifts toward the long wavelength with the addition of Bi gradually. The full width of half maximum (FWHM) is about 200 nm. The broadband infrared luminescence of Bi-doped GeS2-Ga2S3 chalcogenide glasses may be predominantly originated from the low valence state of Bi, such as Bi+. Raman scattering is also conducted to clarify the structure of glasses. These Bi-doped GeS2-Ga2S3 chalcogenide glasses can be applied potentially in novel broadband optical fibre amplifiers and broadly tunable laser in optical communication system.

钛宝石中子辐照色心的研究

研究了中子辐照下钛宝石单晶体缺陷的形成及光学性能的变化。对温度梯度法(TGT)生长的钛宝石晶体进行中子辐照。中子能量为1．5MeV，剂量为4．32×10^18 neutrons／cm^2。辐照后194nm吸收峰强度增加,268nm吸收峰强度则降低。荧光谱检测中发现辐照使得420nm荧光峰强度明显降低，荧光峰位置也蓝移至414nm处。分析表明辐照使得钛宝石晶体内形成F^+缺陷，同时Ti^4+离子则转化成Ti^3+离子。辐照后的钛宝石在247C处有热释光TL出现，通过初始上升法计算出其陷阱深度为0．63eV。

Sites structure and spectroscopic properties of Yb-doped and Yb, Na-codoped CaF2 laser crystals

For the first time, the effect of Na+ on crystal structure, valence state of Yb ions, spectroscopic properties of YbF3-doped CaF2 system was systematically studied. Na+ can greatly suppress the deoxidization of Yb3+ to Yb2+. Absorption and emission spectra showed codoping Na+ with different Na:Yb ratios can modulate the spectroscopy and photoluminescence properties of Yb3+ ions in CaF2 lattice in a large scope. The emission lifetime and quantum efficiency of Yb3+ in CaF2 were greatly enhanced by the codopant of Na+. The potential laser performances of the new Yb, Na-codoped CaF2 crystals were predicted. (c) 2005 Elsevier B.V. All rights reserved.