Optical effects caused by high laser powers in ion-implanted Bi4Ge3O12 waveguides

Abstract

The ‘optical writing’ of permanent channel waveguides in the surface of He⁺ ion-implanted bismuth germanate, Bi₄Ge₃O₁₂, has been studied, using end-coupled argon and Ti:sapphire CW laser beams. Comparisons of the self-focusing effect in waveguides and bulk samples have been made for both Nd³⁺ doped and undoped material. The permanent ‘writing’ effect has been compared with the structural change observed earlier in ion-implanted Bi₄Ge₃O₁₂ waveguides annealed at high temperature.     

Synthesis of a bismuth germanium oxide source material for Bi4Ge3O12 crystal growth

A technique has been developed for the preparation of a modified source material for the crystal growth of bismuth orthogermanate, Bi₄Ge₃O₁₂ (BGO). It includes dispersion of molten bismuth through mixing with germanium oxide (GeO₂) powder in a rotating reactor, followed by oxidation with oxygen. The source material thus prepared contains, in addition to bismuth and germanium oxides, considerable proportions of germanates (Bi₂GeO₅, Bi₄Ge₃O₁₂, and Bi₁₂GeO₂₀), which improve the reactivity of the components of the source material during homogenization before the crystal growth process. After sintering at 880°C, the density of the modified source material (3.9 g/cm³) is a factor of 1.5 higher than that of a source material prepared from Bi₂O₃ and GeO₂ powders. BGO crystals grown using the synthesized source material possess good scintillation characteristics.     

Alteration of amorphous Bi4Ge3O12 by Tl2O and Na2O

Ternary thallium and sodium bismuth germanate glasses were prepared and their densities refractive indices, and infra-red spectra obtained. The effect of univalent cations on the stability of the arrangement of decoupled GeO₄ tetrahedra in amorphous Bi₄Ge₃O₁₂ was compared with the effect of divalent cations. The molar volumes of glasses with the nominal mol% composition 20 M₂O(MO).20 Bi₂O₃.60 GeO₂ are directly related to the size and charge type of M^z+. However, the molar volumes of such glasses are inversely related to the ionic potential (z/r) of M^z+. The infra-red spectra of these ternary glasses exhibitv _Ge?O shifts that reflect the presence of both isolated and small clusters of GeO₄ tetrahedra compared to amorphous Bi₄Ge₃O₁₂. This slight increase in the degree of polymerization appears to be directly related to the ionic potential of M^z+.     

Optical and holographic properties of Bi4Ge3O12 crystals doped with ruthenium

Bi₄Ge₃O₁₂ single crystals doped with different concentration of Ru were grown by the Czochralski technique. Optical absorption bands were induced by illumination with ultraviolet light at room temperature. The absorption coefficient values increased with increasing ruthenium concentration. The induced photochromic effect was completely reversible: all samples recovered their transparency after thermal treatment. Preliminary holographic recording experiments showed a fast response time and a relatively slow erase time during the reading process.     

Planar optical waveguides in Nd:BSO crystals fabricated by He and C ion implantation

Planar optical waveguides in Nd:BSO crystals were fabricated by the implantation of 500 keV He ions and 6.0 MeV C ions at two different substrate temperatures. The guiding modes were measured by the prism-coupling method with a He-Ne beam at 633 nm. The intensity calculation method (ICM) and reflectivity calculation method (RCM) were used for reconstructing refractive index profiles. The near-field intensity distribution of the waveguide, formed by He and C ions implanted after annealing at 300 °C, was measured by the end-face coupling setup. It was in reasonable agreement with the intensity of the waveguide mode simulated by the finite-difference beam propagation method (FD-BPM). The absorption spectra of the sample with He ions implanted at fluences of 3 × 10¹⁶ ions/cm² were measured using a spectrophotometer.     

Planar optical waveguides obtained in Z-cut LiNbO3 and LiTaO3 by proton exchange in LiHSO4 vapors

A new proton source – LiHSO₄ vapors at low temperature – was used in forming optical waveguides in LiNbO₃ and LiTaO₃. The proton-exchanged layers were investigated by mode spectroscopy and infrared absorption spectroscopy. An estimate of the optical losses and phase contents of the waveguides was made. The diffusion parameters were determined for both types of crystal, and were compared to those obtained when benzoic acid melt was used as a proton source. The results presented could contribute to the realization of waveguides with controled phase compositions. The method proposed allows the use of a very simple and safe chamber construction, and the production of low-loss waveguides in a single technological step.     

Preferred crystal orientation of sol-gel-derived Bi4-xLaxTi3O12 thin films on silicon substrates

Polycrystalline thin films of La-substituted bismuth titanate (BLT) were formed directly on p-type Si(100) substrates by using sol-gel and spin coat methods. The BLT film and interfacial layer between BLT and Si were quantitatively investigated by the X-ray reflectivity method. Also, crystal orientations of sub-100-nm-thick BLT thin films were confirmed by X-ray diffraction using a synchrotron radiation source. The preferred c-axis orientation normal to the surface depended on the crystallization temperature. The difference in the preferred c-axis orientations of the BLT films caused the difference in the hysteresis voltage width in the capacitance-voltage characteristics of Au/BLT/p-Si structures. Furthermore, the c-axis of the Bilayered structure was preferentially oriented and aligned in the in-plane direction.     

Sol-gel法制备Bi3.15Nd0.85Ti3O12铁电薄膜的性能研究

用sol-gel法成功制备了Bi3.15Nd0.85Ti3O12铁电薄膜,XRD结果表明制备的BNT薄膜具有(117)和(00l)的混合取向,FE-SEM显示薄膜表面光滑致密,颗粒均匀.剩余极化Pr和矫顽场Ec分别为29.5μC/cm2和100kV/cm,经过109次循环后几乎无疲劳.     

C-axis-oriented Bi3.25La0.75Ti3O12 ferroelectric thin film fabricated by chemical solution deposition

C-axis-oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) ferroelectric thin films were successfully prepared by chemical solution deposition. According to X-ray diffraction, it is found that the orientation degree increases with the increase of sintering temperature, and at the same time the grain morphology changes from equiaxed to plate-like. Due to the dense morphology and [Bi₂O₂]²⁺ layer of c-preferred orientation of BLT film sintered at 650 °C, it exhibits the lowest leakage current density at room temperature. Additionally, a linear relation between V^0.5 and log(J / T²) is found, suggesting the behavior of leakage current of BLT films obeys the Schottky emission model. P–E loops show that the c-axis-oriented BLT ferroelectric film exhibits low polarization and small coercive field.     

熔盐法合成板状钛酸铋微晶

采用熔盐法制备了板状Bi4Ti3O12微晶.用示差扫描量热-热重分析(DSC-TG)、X射线衍射(XRD)及扫描电镜(SEM)研究了不同温度对合成Bi4Ti3O12相结构与形貌的影响.结果表明,板状Bi4Ti3O12微晶的最佳合成温度为800～1000℃,低于800℃合成产物中容易出现杂相;1030℃时Bi4Ti3O12出现结构变化;1165℃出现杂相Na0.5Bi0.5Ti7O27;温度继续升高到1250℃时Bi4Ti3O12出现分解.实现板状Bi4Ti3O12微晶形貌可控的最佳温度范围为850～950℃.     

Effect of High Gamma Doses on the Scintillation and Optical Properties of Bi4Ge3O12 Crystals

Inorganic Materials - We have studied the influence of high gamma doses and dose rates on the light output of bismuth orthogermanate (Bi4Ge3O12) crystals. The results demonstrate that the change in...     

硅衬底Bi4Ti3O12和Bi3.25La0.75Ti3O12铁电薄膜的慢正电子束研究

对硅衬底生长的Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜样品测量了慢正电子多普勒展宽谱,得到了S参数随正电子注入能量的变化。通过对S参数和W参数的分析,讨论了这类材料中的捕获态特征和结构特点,结果表明,薄膜与硅衬底界面的缺陷为空位-氧复合体,La的掺杂有助于阻止空位-氧复合体向界面的扩散。     

非化学计量Bi2O3对制备Bi4Ti3O12粉体影响的研究

制备晶粒形貌生长各向异性的中间化合物Bi4Ti3O12粉体是采用流延成型和模板晶粒生长(TGG)等工艺方法制备(Na0.5Bi0.5)TiO3基无铅压电织构陶瓷的关键技术.以NaCl-KCl熔盐法制备了生长各向异性的Bi4Ti3O12粉体,利用X射线衍射和扫描电子显微镜研究了非化学计量Bi2O3对粉体相结构和微观形貌的影响,优化了制备Bi4Ti3O12粉体的工艺参数,并探讨了Bi4Ti3O12粉体在熔盐中的生长机理.研究表明,随着Bi2O3过量程度的增加,所得Bi4Ti3O12粉体颗粒的平均尺寸和均匀程度均增加,当Bi2O3过量7.5%时达到最佳值,其平均粒径为8～10 μm.