Spectral dependence of the diffraction efficiency of light-induced gratings in YAlO3:Mn crystals

The results of measurements of spectral dependence of diffraction efficiency of light-induced holographic gratings in YAlO₃:Mn(0.5%) crystal are reported. The experimental data are interpreted as an effect of interaction of both refractive index changes and light-induced absorption associated with optical transition within photo-induced Mn⁵⁺ ions and intrinsic defect centers. Nature of the intrinsic traps involved in the process is discussed.     

Two-wave mixing of ion-implanted photorefractive waveguides in near-stoichiometric Fe:LiNbO3 crystals

We report on the two-wave mixing of light in photorefractive waveguides in H ion-implanted Fe-doped near-stoichiometric lithium niobate crystals. For pump light of 632.8 nm wavelength a gain coefficient as high as 15 cm⁻¹ is found. A response time of the order of a few seconds is achieved for micro-watt input powers.     

Time-resolved spectroscopy of intrinsic luminescence of Y3Ga5O12 and (LaLu)3Lu2Ga3O12 single crystals

The nature of intrinsic luminescence of Y₃Ga₅O₁₂ (YGG) and (LaLu)₃Lu₂Ga₃O₁₂ (LLGG) single crystals grown from a melt was determined. In the case of a YGG single crystal containing Y_Ga antisite defects with a concentration of 0.25–0.275 at.% the intrinsic luminescence was considered as a superposition of luminescence of self-trapped excitons (STE), luminescence of excitons localized near antisite defects (LE(AD) centers) and luminescence caused by a recombination of an electron with a hole captured at Y_Ga antisite defects. Due to a large (2–3%) concentration of Lu_La antisite defects in LLGG single crystals the intrinsic luminescence was a superposition mainly of the LE(AD) center emission and the recombination luminescence of Lu_La antisite defects. The energy structure of the mentioned centers in YGG and LGGG hosts was determined from the excitation spectra of their luminescence under excitation by synchrotron radiation in the range of the fundamental absorption edge of these garnets.     

Microstructural study of YBa2Cu3O7/SrTiO3/YBa2Cu3O7 heteroepitaxial trilayer films grown on (100) SrTiO3 substrates

Detailed transmission electron microscopic study has been carried out on heteroepitaxial YBa₂Cu₃O₇/SrTiO₃/YBa₂Cu₃O₇ trilayer thin films grown on (100)SrTiO₃ substrates prepared by DC and RF magnetron sputtering. The microstructural results showed the existence of somea-axis-oriented YBCO grains 20–90 nm wide in thec-axis-oriented YBCO matrix. Some of thea-axis grains in the lower YBCO thin film layer have protruded into the above SrTiO₃ layer, which may cause short circuit between the two YBCO superconducting layers. This is unsuitable for the application of trilayer thin films for microelectronic devices. The defects on the surface of the substrates would also influence the growth quality of the YBCO thin films.     

Phase developments in the Pb(Zn1/2W1/2)O3-Pb(Zn1/3Ta2/3)O3-Pb(Zn1/3Nb2/3)O3 pseudo-ternary system

The phase stability ranges in the B-site precursor (Zn_1/2W_1/2)O₂-(Zn_1/3Ta_2/3)O₂-(Zn_1/3Nb_2/3)O₂ were determined by X-ray diffraction (XRD), where wolframite, tri-αPbO₂, and columbite phases were identified. Next attempts were carried out (with the addition of PbO) for the system Pb(Zn_1/2W_1/2)O₃-Pb(Zn_1/3Ta_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃, where the perovskite phase did not develop in the entire compositions investigated. Instead, only the Pb₂WO₅ and pyrochlore phases (along with ZnO) resulted.     

Elastic modulus and hardness of CaTiO3, CaCu3Ti4O12 and CaTiO3/CaCu3Ti4O12 mixture

Three ceramic systems, CaTiO₃ (CTO), CaCu₃Ti₄O₁₂ (CCTO) and intermediate nonstoichiometric CaTiO₃/CaCu₃Ti₄O₁₂ mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO.     

Concentration effects on Pr luminescence in LaAlO3 crystals

Concentration dependant emission spectra and fluorescence dynamic profiles have been investigated in Pr_xLa_1−xAlO₃ single crystals in order to better understand processes responsible for concentration quenching of the praseodymium ³P₀ and ¹D₂ emissions. The cross-relaxation transfer rates were experimentally determined as a function of Pr³⁺ concentration. Decays were modeled and nearest-neighbor trapping rates were calculated.     

Optical properties of Sm doped Mg:LiNbO3 and Zn:LiNbO3 single crystals

Sm³⁺ doped Mg:LiNbO₃ and Zn:LiNbO₃ are grown by Czochralski method. Optical transmittance and emission spectra are measured and Judd-Ofelt theory is applied to determine phenomenological intensity parameters, oscillator strengths, radiant transition rates, total radiant lifetimes, and branching ratios. The calculations show that Judd-Ofelt parameters with the relation of Ω₄ > Ω₂ > Ω₆ exist, and ΣΩ_ξ (ξ = 2, 4 and 6) in Sm:Zn:LiNbO₃ decreases. Fluorescence spectra indicate that visible fluorescence of Sm³⁺ is made up of 570, 606, 613 and 654 nm emission bands in these crystals under 409 nm excitation.     

Thermoluminescence properties of Ce-doped LiSr4(BO3)3 phosphor

Borates LiSr₄(BO₃)₃ were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce³⁺-activated LiSr₄(BO₃)₃ were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce³⁺ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr₄(BO₃)₃:0.01Ce³⁺ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce³⁺.     

Distribution of pyrochlore phase in Pb(Mg1/3Nb2/3)O3-PbTiO3 films and suppression with a Pb(Zr0.52Ti0.48)O3 interfacial layer

Thin films of the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) on Pt/Ti/SiO₂/Si (Pt/Si) substrates both with and without a Pb(Zr_0.52Ti_0.48)O₃ (PZT) interfacial layer were investigated. Perovskite and pyrochlore coexistence was observed for PMN-PT thin films without a PZT interfacial layer. Interestingly, most of the pyrochlore phase was observed in single-coated films and in the first layer of multi-coated films. The pyrochlore phase exhibited grains with an average size of about 25 nm, which is smaller than those of the perovskite phase (about 90 nm). In contrast, for PMN-PT thin films grown on a PZT interfacial layer, the formation of a pyrochlore phase at the interface between PMN-PT layers and the substrate is completely suppressed. Moreover, small grains are not observed in the films with a PZT interfacial layer. The measured polarization-electric field (P-E) hysteresis loops of PMN-PT films with and without PZT layers indicate that enhanced electrical properties can be obtained when a PZT interfacial layer is used. These enhanced properties include an increase in the value of remanent polarization P_r from 2.7 to 5.8 μC/cm² and a decrease in the coercive field E_c from 60.5 to 28.0 kV/cm.     

Determination of the chemical diffusion coefficient of lithium in Li3V2(PO4)3

The chemical diffusion of lithium ion in Li₃V₂(PO₄)₃ were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The CV results show that there exists a linear relationship between the peak current (i_p) and the square root of the scan rate (ν^1/2). The impedance spectrum exhibits a single semicircle and a straight line in a very low frequency region. A linear behavior was observed for every curve of the real resistance as a function of the inverse square root of the angular frequency in a very low frequency region. The obtained chemical diffusion coefficient from EIS measurements varies within 10^− 9 to 10^− 8 cm²·s^− 1, in good agreement with those from CV results.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Spectroscopy and upconversion processes in YAlO3:Ho crystals

Emission from the high lying excited states, energy transfer, and upconversion processes are investigated in YAlO₃:Ho³⁺. Selectively excited emission spectra in the range from 300 to 800 nm starting from the ³D₃, ³G₅, ⁵F₃, ⁵S₂ and ⁵F₅ multiplets were measured at 15 K. This, together with the detailed absorption and excitation measurements at 15 K allowed determination of the Stark energy levels of Ho³⁺ ions in YAlO₃ up to UV energies. The ⁵S₂ fluorescence decays were recorded as a function of temperature and Ho³⁺ concentration in order to investigate the process of quenching of fluorescence due to cross relaxation among two ions. Conversion of red and infrared laser radiation to green ⁵S₂ and blue ⁵F₃ emission is reported. Under pulsed resonant excitation of the ⁵F₅ or ⁵I₅ levels the upconversion was found to be due to energy transfer process between two excited ions. The photon avalanche effect was observed under cw excitation around 585 nm.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

Ca4REO(BO3)3 crystals for green and blue microchip laser generation: from crystal growth to laser and nonlinear optical properties

We have taken advantage of congruent melting behavior of the nonlinear rare-earth oxoborate Ca₄REO(BO₃)₃ family to perfect a process of collective fabrication of self-frequency doubling microchip laser based on Nd:GdCOB (Ca₄Gd_1−xNd_xO(BO₃)₃) crystals. The process goes from Czochralski boule to 1 × 3 mm² chips perfectly oriented (better than 0.1°) to the phase matching direction (θ=90°, φ=46°) in the XY principal plane, with dielectric mirrors directly deposited on both faces of the chips. 20 mW of self-frequency doubling output power at 530 nm was performed under 800 mW of diode laser as incident pump power at 812 nm. In addition, new compositions from the solid solution Ca₄Gd_1−xY_xO(BO₃)₃ (Gd_1−xY_xCOB) (x=0.13, 0.16, 0.44) have been grown by the Czochralski pulling method, in order to achieve noncritical phase matching (NCPM) second harmonic generation of ⁴F_3/2 → ⁴I_9/2 Nd³⁺ doped laser hosts. Three types of laser wavelengths have been chosen: Nd:YAP (YAlO₃) at 930 nm, Nd:YAG (Y₃Al₅O₁₂) at 946 nm, and Nd:ASL (Nd_ySr_1−x La_x−yMg_x Al_12−xO₁₉) at 900 nm. Angular acceptance measurements of these three types of compositions present very large values, compared to pure GdCOB or YCOB oriented in critical phase matching configurations.     

La2O3、Nd2O3、Y2O3对高岭石高温相变动力学的影响

利用综合热分析技术、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和扫描电镜(SEM)研究了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温条件下转变成莫来石过程的作用,并采用Kissinger方程、Ozawa方程以及JMA修正方程(Ⅰ)和(Ⅱ)分析了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温相变动力学的影响。结果表明:3种稀土氧化物的掺入对高岭石的相变动力学参数产生了影响,相变活化能和频率因子与未掺入稀土氧化物的高岭石相比有所降低,析晶方式则未发生变化,均属于体积晶化。对比掺入3种稀土氧化物的高岭石相变活化能和频率因子可以看出,Y_2O_3对于高岭石高温条件下相变的促进作用最为明显,相变活化能最低。稀土氧化物对于高岭石高温相变产物影响不大,主晶相为莫来石相,次晶相为方石英相,但稀土氧化物的掺入使得方石英相的结晶度明显提高。     

Temperature dependence of the infrared optical properties of YBa2Cu3O7: A plasmon damping model

The temperature dependence observed in the mid- and near-infrared optical properties of YBa₂Cu₃O₇ is explained in terms of the Drude model for free charge carriers. In the Drude model, the linear temperature dependence of the dc resistivity arises from the free charge carriers having a temperature-dependent mean free path. This temperature dependence results in the plasmon contribution to the dielectric constant having a damping coefficient which also varies linearly with temperature. We find that the temperature dependence which is observed in the absorption and reflection spectra of YBa₂Cu₃O₇ is consistent with this simple model.     

Colossal magnetocapacitance effect in BiFeO3/La5/8Ca3/8MnO3 epitaxial films

A colossal magnetocapacitance in magnetic fields was observed near the Curie temperature T_c = 220 K of La_5/8Ca_3/8MnO₃ for the BiFeO₃/La_5/8Ca_3/8MnO₃ epitaxial film. It was found that the magnetocapacitance increases with increasing magnetic fields and reaches a maximum up to 1100% enhancement around T_c at 10 T. From the analysis of the dielectric relaxation, one can see that the behavior of relaxation time τ above T_c differs from that below T_c, and the value of τ decreases with increasing magnetic fields. This colossal magnetocapacitance effect near room temperature in BiFeO₃/La_5/8Ca_3/8MnO₃ may have potential applications in multifunctional microelectronic device.     

Flame aerosol deposition and annealing of Y3Al5O12:Tb phosphor coatings

Sub-micrometer-sized powders of Y₃Al₅O₁₂:Tb phosphor (d_SEM = 320 nm) were prepared by flame-assisted spray pyrolysis of aqueous precursors in a premixed propane/air flame and in situ deposited onto quartz substrates. Phosphor screens with densities of up to 0.7 mg cm⁻² could be produced within 20 min. As-deposited coatings were amorphous and required a thermal post-treatment. After annealing in an oven for 2 h (T ≥ 900 °C), the yttrium aluminum garnet phase (YAG:Tb) was obtained. Alternatively, the phosphor coatings were treated by an impinging flame in the same setup used for the deposition. Quasi-amorphous Y₃Al₅O₁₂:Tb coatings demonstrated bright green photoluminescence upon flame annealing at T ≈ 1100 °C for just several minutes and could outperform YAG:Tb when excited in the wavelength ranges 205–220 nm and 230–260 nm. For example, brightness of emission from the quasi-amorphous coatings was up to five times higher than that of the fully crystalline YAG:Tb phosphor at a technically important wavelength of 254 nm.     

Chemical vapor deposition of NiSi using Ni(PF3)4 and Si3H8

NiSi_x films were deposited using chemical vapor deposition (CVD) with a Ni(PF₃)₄ and Si₃H₈/H₂ gas system. The step coverage quality of deposited NiSi_x was investigated using a horizontal type of hot-wall low pressure CVD reactor, which maintained a constant temperature throughout the deposition area. The step coverage quality improved as a function of the position of the gas flow direction, where PF₃ gas from decomposition of Ni(PF₃)₄ increased. By injecting PF₃ gas into the Ni(PF₃)₄ and Si₃H₈/H₂ gas system, the step coverage quality markedly improved. This improvement in step coverage quality naturally occurred when PF₃ gas was present, indicating a strong relationship. The Si/Ni deposit ratio at 250 °C is larger than at 180 °C. It caused a decreasing relative deposition rate of Ni to Si. PF₃ molecules appear to be adsorbed on the surface of the deposited film and interfere with faster deposition of active Ni deposition species.