Anisotropic properties of self-flux grown LiB3O5 single crystals

In this paper, we report the existence of anisotropic behavior along the crystallographic axes in optical, electrical and thermal properties of lithium tri borate, a recently developed vacuum UV-NLO material. The variation of refractive index with the wavelength along the crystallographic axes was investigated by prism coupling method. The results of impedance spectroscopy measurement reveal the presence of a strong anisotropy in ionic conductivity and dielectric constant along the axes and also show the super-ionic conduction behavior along the c-axis with the activation energy of Δ∼0.20 eV. A thermo-mechanical study in the temperature range of 300-900 K indicates the existence of a strong variation in the linear thermal expansion coefficient (positive value along the a-axis, and negative value along the c-axis) of LiB₃O₅ crystals.     

The optical properties of planar waveguides in LiB3O5 crystals formed by Cu implantation

A planar optical waveguide has been formed in a LiB₃O₅ crystal using 6.0 MeV Cu⁺-ions with a dose of 1 × 10¹⁵ ions/cm² at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE₀ and TM₀ modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change.     

Photo- and thermostimulated processes in α-Al2O3

We reported on the recombination processes determined by the release of electrons from defects connected with the dosimetric 430 K thermostimulated luminescence (TSL) peak as well as with the 260 K TSL peak. These TSL peaks appear in thermochemically reduced α-Al₂O₃ crystals containing hydrogen and emission of these TSL peaks corresponds to luminescence of the F-center. The X-ray exposure or UV excitation in the absorption band of F-centers at 6.0 eV of reduced α-Al₂O₃ crystals doped with acceptor impurities results in the appearance of a broad anisotropic complex absorption band in the spectral region 2.5–3.5 eV and in the appearance of a predominant TSL peak at 430 K. Above 430 K the above-mentioned broad absorption band disappears. Optical bleaching of the 2.5–3.5 eV band is accompanied by the disappearance of the 430 K TSL peak and results in F-center emission. The X-ray or UV excitation of reduced α-Al₂O₃ crystals with donor-type impurities results in the appearance of an anisotropic absorption band at 4.2 eV and the appearance of a dominant TSL peak at 260 K. Above 260 K the 4.2 eV absorption disappears and photostimulated luminescence (PSL) of the F-center recombination luminescence in the 4.2 eV region is no longer observed. Optical bleaching of the 4.2 eV absorption band is accompanied by the disappearance of the 260 K TSL peak. The successful use of reduced α-Al₂O₃ in dosimetry needs the optimization of the concentration of all components (acceptors, hydrogen, intrinsic defects) involved in the thermo- and photostimulated processes.     

LiB3O5单晶的偏振喇曼散射谱

在室温下测量了LiB₃O₅单晶的各种振动类的偏振喇曼散射谱。利用因子群分析和变温测量等方法以及BO₃,BO₄基团振动谱带的结果,对振动模进行了初步指认。根据LO-TO劈裂的实验结果,计算出该晶体的静态介电系数和各极化模的有效电荷。 关键词：     

LiB3O5晶体高温拉曼光谱研究

研究了LiB₃O₅晶体在不同温度下(在300—1173K的温度范围)的拉曼光谱,分析了LBO晶体结构随温度变化的规律.随着温度的升高,LBO晶体的拉曼光谱谱峰都不同程度地向低波数方向移动,也存在不同程度的展宽,同时强度减弱.发现晶体在1100K存在明显相变,与LBO晶体的相图给出的1107K的相变温度基本相符. 关键词： 3O₅晶体')" href="#">LiB₃O₅晶体 高温拉曼光谱 相变     

Thermostimulated recombination processes in LiBaF3 crystals

The creation of radiation defects in LiBaF₃ crystals at 10 K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270 K. Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20 K arises from the delocalization of H-centers. The presence of two TSL peaks related to V_K-centers at 105 and 130 K indicates that 60° and 90° migration hops occur.     

Radiative and non-radiative transitions in ErP5O14 single crystals

The radiative and non-radiative transitions from excited states of ErP₅O₁₄ were studied on the basis of the Judd-Ofelt theory and experimental data. It was shown that the non-radiative relaxations, predominantly multiphonon emission, are very effective in the depopulation of excited states of erbium in erbium pentaphosphate crystals. The concentration quenching of erbium fluorescence is found to be small.     

Insulator-metal transition in V3O5

The results of a study of the insulator-metal phase transition in V₃O₅ occuring at T = 450 K are presented. Conductivity, thermopower, magnetic, structural and optical data are reported. On a basis of the data obtained we conclude that the high-temperature phase is a poor metal with strong electron correlations and localized magnetic moments. The metal-non-metal transition is presumably driven by the spatial ordering of V³⁺ and V⁴⁺ ions.     

Color centers in neutron-irradiated Y3Al5O12, CAF2 and LiF single crystals

The thermal annealing behavior of the Y₃Al₅O₁₂, CaF₂ and LiF single crystals bombarded at Algiers with reactor neutrons has been monitored by optical absorption spectroscopy. The irradiation was performed at about 315 K. On heating samples after irradiation, the optical absorption bands decrease and disappear completely at 873 and 523 K in the case of Y₃Al₅O₁₂ and CaF₂, respectively. Activation energies of 1.2±0.02 and 0.9±0.2 eV are estimated for Y₃Al₅O₁₂ and CaF₂, respectively. On the other hand, the LiF crystal shows a complex annealing behavior. Here, the optical absorption spectrum presents different shapes after each annealing temperature. Four steps are distinguished and discussed on heating samples from 300 to 673 K. Above 673 K, the absorption drops by about 50%; it completely disappears at 773 K.     

Luminescence of Fe3+ in single crystals of LiAl5O8

We have measured the luminescent properties of single crystals of LiAl₅O₈:Fe³⁺. In addition to a zero-phonon line due to Fe³⁺ in A-sites, we have observed another sharp fluorescent line at 699.2 nm which we assign to Fe³⁺ occupying B-sites. The excitation spectrum of the B-site Fe³⁺ shows characteristics similar to those of the A-site Fe³⁺ but are also shifted towards longer wavelengths. The spectra of the single crystals are compared with those of ordered and disordered powder samples.     

Dielectric dispersion in PbO-Sb2O3-As2O3:V2O5 glasses

Dielectric properties, viz. dielectric constant ε′, loss tan δ and a.c conductivity σ_ac (over a wide range of frequency and temperature) and dielectric breakdown strength of PbO-Sb₂O₃-As₂O₃ glasses doped with V₂O₅ (ranging from 0 to 0.5 mol%) are studied. Analysis of these results, based on optical absorption and ESR spectra, indicates that the insulating strength of the glasses is comparatively high when the concentration of V₂O₅ is about 0.3 mol% in the glass matrix.     

Curie temperatures of Y3Fe5O12/Gd3Fe5O12 superlattices

The magneto-optical Kerr effects (MOKE) of epitaxial Y₃Fe₅O₁₂/Gd₃Ga₅O₁₂ (YIG/GGG) garnet superlattices grown on (1 1 1)GGG previously by pulsed laser deposition (PLD) were measured. A series of superlattices were investigated with the thickness of the ferrimagnetic YIG layer varied from six unit cells to only one unit cell while keeping the Curie paramagnetic GGG fixed at one unit cell. It was demonstrated that the ellipsometric technique employing photoelastic modulators (PEM) is sensitive enough to measure the MOKE signals of these ultrathin oxide samples. The Curie temperatures, determined by MOKE, are fit with a power law, yielding a shift exponent λ = 3.1 ± 1.2.     

Radiative and nonradiative processes in LiGa5O8: Mn

The luminescence of LiGa₅O₈:Mn⁴⁺ was observed with measurements of decay times and intensities for different temperatures. The experimental results were analysed taking into account purely radiative, vibronic and radiationless transitions. It is shown that the nonradiative process involves 46 phonons, each with an energy of 304 cm⁻¹.     

UV-induced two-photon absorption in BiB3O6 single crystals

We show that BiB₃O₆ (BiBO) crystals, well known for their excellent second harmonic generation (SHG) properties, may also be of interest for third-order optical phenomena, particularly for two-photon absorption (TPA). Photoinduced TPA measurements were performed under illumination of excimer Xe–F laser (λ = 217 nm) as a photoinducing (pumping) beam. It created a thin surface layer (about 85 nm) that was a source of the observed photoinduced TPA. Raman shifted Nd-YAG laser radiation (λ = 1.9 μm) as well as its second and fourth harmonics (λ = 950 and λ = 475 nm, respectively) were used as fundamental (probing) beams of the TPA. The highest values of the TPA β coefficient were achieved for a polarization of the pumping light directed along crystallographic axis b. Quantum chemical simulations indicate on substantial contribution of UV-induced electron–phonon anharmonicity to the observed TPA. The obtained values of TPA coefficients indicate a possibility of using BiBO crystals as UV-operated optical limiters in a wide spectral range.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

Magnetic and structural studies of Cr2O5 and Cr3O8

The infrared spectra, indexed X-ray powder diffraction patterns, magnetic susceptibilities between 80 and 300 K, and electron paramagnetic resonance spectra at 80 and 300 K are reported for Cr₂O₅ and Cr₃O₈. The results indicate that both oxides are Cr³⁺/Cr⁶⁺ mixed-valence compounds which contain CrO₆ octahedra and CrO₄ tetrahedra in different ratios. The valence formula for Cr₂O₅ is Cr³⁺₂Cr⁶⁺₄O₁₅ and that of Cr₃O₈ is Cr³⁺₂Cr⁶⁺₇O₂₄. The X-ray powder data for Cr₂O₅ and Cr₃O₈ could be indexed on the basis of a monoclinic unit cell $\text{(a = 12.01(2), b = 8.52(1), c = 9.39(1)}\text{A}\text{?}\text{β = 92.0(1)°)}$ and an orthorhombic unit cell $\text{(a = 12.01(7), b = 36.60(7) and c = 3.82(1)}\text{A}\text{?}\text{)}$, respectively.     

Semiconductor-metal transition in v-doped Ti3O5

The semiconductor-metal transition in Ti₃O₅ is significantly affected by vanadium doping. The unit cell volume, ΔH, Δ? as well as Δ_χM decrease markedly up to 0.1% V₃O₅ and gradually thereafter until at ～ 10% V₃O₅, the transition disappears.     

Determination of trapping parameters of dosimetric thermoluminescent glow peak of lithium triborate (LiB3O5) activated by aluminum

Lithium triborate (LBO) is a newly developed ideal nonlinear optical (NLO) crystal used in laser weapon, welder, radar, tracker, surgery, communication, etc. The effective atomic number (Z_eff=7.3) makes it a tissue equivalent material and this encourages studies on its thermoluminescence (TL) properties for a radiation dosimetry. The previous studies have shown that Al-doped LiB₃O₅ is a promising thermoluminescent dosimetric (TLD) material for dosimetric purposes and continuous and systematic investigations to improve its quality to get ones suited for dosimeter applications are worthy. In the given study, the additive dose (AD), initial rise with partial cleaning (IR), variable heating rate (VHR), peak shape (PS), three-points method (TPM) and computerized glow deconvolution (CGCD) methods were used to determine the kinetic parameters, namely the order of kinetics (b), activation energy (E_a) and the frequency factor (s) associated with the dosimetric thermoluminescent glow peak (P3) of Al-doped LiB₃O₅ after different dose levels with β-irradiation.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Esca studies of Ga,As, GaAs,Ga2O3, As2O3 and As2O5

The binding energies of Ga 3d, As 3d, Ga L₃M₄,₅M₄,₅ and O 1s in Ga, As, GaAs, Ga₂O₃, As₂O₃ and As₂O₅ are reevaluated by means of ESCA. The calibration lines of the C 1s and the Au 4f_{$\text{7}\text{2}$} gave different binding energies for the compound materials. In order to determine the absolute binding energies, the chemical shifts in Auger and photoelectron lines from a layered structure composed of thin layer oxide and substrate of a defined material were used. An energy calibration curve, E(Ga 3d) vs. ΔE(GA LMM - Ga 3d), was found to be useful for determination of binding energies in the material which contains gallium. In the case of the GaAs sample, both the chemical etching and the ion bombardment effects on the chemical structure of the GaAs surface are also discussed.