Spectral parameters of Nd3+ ion in Nd<Superscript>3+</Superscript>:LaCa<Subscript>4</Subscript>O(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystal

The spectral parameters of Nd³⁺ ions in Nd:LaCa₄O(BO₃)₃ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters Ω_λ are Ω₂ =1.98 × 10^–20 cm², Ω₄ =2.39 × 10^–20 cm², Ω₆ =1.38 × 10^–20 cm², the radioactive lifetime is 655 μs, the quantum efficiency is 10%, and the fluorescence branch ratios were calculated: β₁ = 0.51, β₂ = 0.42, β₃ = 0.066, β₄ = 0.003. Electronic Publication     

Spectral parameters of Er<Superscript>3+</Superscript> ion in Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The spectral parameters of Er³⁺ in Yb³⁺/Er³⁺:KY(WO₄)₂ crystal with space group C2/c have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters are: ₂ = 6.33 × 10^–20 cm², ₄ = 1.35 × 10^–20 cm², ₆ = 1.90 × 10^–20 cm². The radiative lifetime and the fluorescence branch ratios were calculated. The emission cross section _e (at 1536 nm) is 2.0 × 10^–21 cm².     

Spectral parameters of Nd3+ ion in Nd:KLa(WO4)2 crystal

The spectral parameters of Nd³⁺ ions in Nd:KLa(WO₄)₂ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the parameters of oscillator strengths are Ω₂=3.0887×10^–20 cm², Ω₄=1.0375×10^–20 cm², Ω₆=1.0422×10^–20 cm², the radiative lifetime is 685 μs, the quantum efficiency is 30.7%, and the fluorescence branch ratios were calculated: β₁=0.432, β₂=0.475, β₃=0.089, β₄=0.004. Electronic Publication     

Phonons in mixed superionic fluorites (BaF<Subscript>2</Subscript>)<Subscript>1-x</Subscript>(LaF<Subscript>3</Subscript>)<Subscript>x</Subscript>

In recent years, the fluorite-structured solid solutions with the general formula, (MF₂)_1-x(RF₃)_x (M = Ca, Sr, Ba, Pb and R is a rare-earth element or Y), have been the subject of numerous experimental studies focussed on their superionic properties. The overall cubic crystal symmetry (space group Fm3m) is conserved up to x ≶ x_max, where x_max ⊁ 0.4-0.5 depending on M and R. The zone centre phonons and phonon dispersion along three symmetry directions of the mixed superionic compound (BaF₂)_1-x(LaF₃)_x have been investigated by applying de Launey angular force model for x ≶ x_max. The calculated results are compared and explained with available experimental results.     

Growth of Nd<Superscript>3+</Superscript> doped LiNbO<Subscript>3</Subscript> crystals using Bridgman method and its spectral properties

The growth of Nd³⁺ doped lithium niobate crystals using Bridgman method has been reported in this paper. By means of the optimum conditions such as proper feed materials, sealed platinum crucibles, growth rate of 1–1·5 mm/h and temperature gradient of 30–35°C/cm across the solid-liquid interface under the furnace temperature of 1300°C, single crystals containing Nd³⁺ ion with 0·54 mol% concentration were obtained. X-ray diffraction and ICP-AES were used to characterize the crystals and its composition. The absorption, emission and fluorescence lifetime are also measured. Based on the Judd-Ofelt theory, we obtained the optical parameters of the crystal such as the luminescent quantum efficiency, the radioactive lifetimes, the branching ratios and the emission cross-section.     

Bridgman growth and defects of Nd<Superscript>3+</Superscript> : Sr<Subscript>3</Subscript>Ga<Subscript>2</Subscript>Ge<Subscript>4</Subscript>O<Subscript>14</Subscript> laser crystals

Nd³⁺ : Sr₃Ga₂Ge₄O₁₄ crystals have been grown by the modified Bridgman method. The growth defects, such as striations, scattering particles and dislocations were investigated. Some featherlike striations were observed in as-grown crystals. EPMA analysis suggested that these inclusions were caused by the segregation of Nd₂O₃ from the melt. Chemical etching results showed that the dislocation density was in the range of 10³ ∼ 10⁵/cm².     

Superconducting Properties of Iodine-Intercalated Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10+<Emphasis Type="Italic">x</Emphasis></Subscript>

The superconducting properties of iodine-intercalated high-temperature superconducting Bi₂Sr₂Ca₂Cu₃O_10+x phase (Bi-2223) were systematically studied. It was found that for samples containing a significant amount of Bi₂Sr₂CaCu₂O_8+x , iodine intercalation results in the dramatic decrease of the inter-granular critical current density, as well as a significant decrease of the critical temperature (T _c), the critical current density in the grains (J _cg), and of the amount of Bi-2223. For samples with a large amount of Bi-2223, T _c changes insignificantly, whereas J _cg can even increase. We argue that the different behavior of the superconducting parameters is the result of various oxygen concentrations, and we explain the effect of iodine intercalation based on the parabolic dependence between T _c and the number of holes per CuO₂ layer. The H(T) curves (determined from the peak position in the loss signal of ac susceptibility) for intercalated samples deviate significantly from the quasi 2D-like behavior, pointing toward an enhancement of the 3D fluctuations of vortices. For the change in the values and dimensionality of the flux pinning in the process of the intercalation, we attempted a qualitative explanation based on the models proposed in literature.     

Structural,optical and non-linear investigation of Eu<Superscript>3+</Superscript>: Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> sol-gel glass

Optical absorption and fluorescence spectra of Eu³⁺ ions in Al(NO₃)₃-SiO₂ sol-gel glass have been investigated using the Judd- Ofelt theory. JO intensity parameters (ω _λ ) and subsequent radiative properties for⁵ D ₀ ↔⁷ F _1,2,4,6 transitions are determined. The lifetime (τ_r) of⁵ D ₀ state is computed and along with JO parameters are compared with their corresponding values in other glasses prepared by conventional technique. A structural analysis, using IR and XRD spectra and non- linear parametrization of the silica gel glass is carried out. The study reveals the glass to be a very good third order non- linear amorphous optical material.     

Preparation and characterization of Eu<Superscript>3+</Superscript> activated CaSiO<Subscript>3</Subscript>, (CaA)SiO<Subscript>3</Subscript> [A = Ba or Sr] phosphors

Eu³⁺ activated CaSiO₃, (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ have been prepared by sol-gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu³⁺ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to⁵D₀ →⁷F₂ transition of Eu³⁺ ion in (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ phosphors, when excited by 254 nm. The (Ca, Ba) SiO₃ material is proposed as an efficient red phosphor.     

Study of gel grown mixed crystals of Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>(IO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The growth of mixed crystals of Ba _x Ca_1−x (IO₃)₄ were carried out with simple gel method. The effect of various parameters such as pH of gel solution, gel concentration, gel setting time, concentration of reactants on the growth was studied. Crystals having different morphologies and habits were obtained. The grown crystals were characterized by XRD, FT-IR, EDAX, TGA, DTA and DSC.     

Emission analysis of Pr<Superscript>3+</Superscript> &; Ho<Superscript>3+</Superscript>: Ca<Subscript>4</Subscript>GdO(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> powder phosphors

Emission spectral results of Pr³⁺ & Ho³⁺ ions doped Ca₄GdO(BO₃)₃ powder phosphors are reported here. XRD, SEM and FTIR measurements have been carried out for them. The emission spectrum of Pr³⁺: Ca₄GdO(BO₃)₃ has shown an emission transition ¹D₂ → ³H₄ at 606 nm with λ_exci = 480 nm (³H₄ → ³P₀) and Ho³⁺: Ca₄GdO(BO₃)₃ phosphor has shown an emission transition ⁵S₂ → ⁵I₈ at 549 nm with λ_exci = 447 nm (⁵I₈ → ⁵F₁). Emission performances of these two phosphors have been explained in terms of energy level diagrams.     

Impedance analysis of Pb<Subscript>2</Subscript>Sb<Subscript>3</Subscript>LaTi<Subscript>5</Subscript>O<Subscript>18</Subscript> ceramic

Polycrystalline sample of Pb₂Sb₃LaTi₅O₁₈, a member of tungsten- bronze (TB family, was prepared using a high temperature solid- state reaction technique. XRD analysis indicated the formation of a single-phase orthorhombic structure. The dielectric studies revealed the diffuse phase transition and the transition temperature was found to be at 52° C. Impedance plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed Debye relaxation. The activation energy was estimated to be 0·634 eV from the temperature variation of d.c. conductivity. The nature of variation of d.c. conductivity with temperature suggested NTCR behaviour.     

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.     

Preparation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Buffer Layer on LaAlO<Subscript>3</Subscript> Substrate by TFA-MOD Method

Chemical solution deposition is a promising technique for fabrication of high-temperature superconducting films and oxide buffer layers due to its reproducibility and low cost. In this work, Y₂O₃ buffer layers were prepared on (100) LaAlO₃ substrates by mental organic deposition method using trifluoroacetate. The resulting Y₂O₃ films crystallized as a single phase at 900°C and showed a low degree ofc-axis orientation. The scanning electron micrography showed that the surface of the films was smooth with a uniform grain size of approximately 10 nm.     

Crystal Electric Field Excitations in the Non-Fermy Liquid Compound YbRh<Subscript>2</Subscript>Si<Subscript>2</Subscript>

We have calculated the crystalline electric field (CEF) splitting of the energy levels of Yb³⁺ (4f¹³) in the clean Yb-based heavy fermion compound YbRh₂Si₂. The data of inelastic neutron scattering and electron spin resonance measurements in YbRh₂Si₂, together with relevant structural, thermodynamic, and magnetic properties, were used as input in the calculations of the possible CEF level scheme in this non-Fermi-liquid compound. Two possible sets of the CEF parameters with the Γ₆ or Γ₇ ground-state symmetry are discussed. PACS: 71.27.+a; 75.20.Hr; 76.30.−v.     

Single phased Sr<Subscript>3</Subscript>La(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>:Eu<Superscript>2+</Superscript>/Mn<Superscript>2+</Superscript> phosphors: solid state synthesis,tunable luminescence and potential applications in white light LEDs

A series of Sr₃La(PO₄)₃:Eu²⁺/Mn²⁺ phosphors were synthesized by a solid state reaction. The phase and the optical properties of the synthesized phosphors were investigated. The XRD results indicate that the doped Eu²⁺ and Mn²⁺ ions do not change the phase of Sr₃La(PO₄)₃. The peak wavelengths of Eu²⁺ single doped and Eu²⁺/Mn²⁺ codoped Sr₃La(PO₄)₃ phosphors shift to longer wavelength due to the larger crystal field splitting for Eu²⁺ and Mn²⁺. The increases of crystal field splitting for Eu²⁺ and Mn²⁺ are induced by the substitution of Sr²⁺ by Eu²⁺ and Mn²⁺ in Sr₃La(PO₄)₃ host. Due to energy transfer from Eu²⁺ to Mn²⁺ in Sr₃La(PO₄)₃:Eu²⁺/Mn²⁺ phosphors, tunable luminescence was obtained by changing the concentration of Mn²⁺. And the white light was emitted by Sr₃La(PO₄)₃:3.0 mol%Eu²⁺/4.0 mol%Mn²⁺ and Sr₃La(PO₄)₃:3.0 mol%Eu²⁺/5.0 mol%Mn²⁺ phosphors.     

Enhanced Superconducting Properties of Air-Processed GdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript> Single Domains with BaCO<Subscript>3</Subscript>/BaCuO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Addition

Single domain GdBa₂Cu_7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed Gd123 was successfully enhanced by addition of both BaCO₃ and BaCuO_2−x , which suppress the formation of Gd_1+x Ba_2−x Cu₃O_7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO₃ and 0.05 to 0.1, M BaCuO_2−x per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band formed by Gd₂BaCuO₅ particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and 8, mm in thickness and a high critical current density J _c up to 91,200, A/cm² was achieved at 77, K under self-field.     

Crystal structure and luminescence property of a single-phase white light emission phosphor Sr<Subscript>3</Subscript>YNa(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F:Dy<Superscript>3+</Superscript>

A series of single-phase Sr₃YNa(PO₄)₃F:Dy³⁺ phosphors were successfully synthesized via a conventional solid state reaction process. The powder X-ray diffraction patterns were utilized to confirm the phase composite and crystal structure. The phosphor could be excited by the ultraviolet visible light in the region from 300 to 420 nm, and it shown two dominant emission bands peaking at 484 nm (blue light) and 580 nm (yellow light) which originated from the transitions of ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 of Dy³⁺, respectively. The optimum dopant concentration of Dy³⁺ ions was confirmed to be 7 mol% in Sr₃YNa(PO₄)₃F:Dy³⁺ system and the concentration quenching mechanism is dipole–dipole interaction. The lifetime values of Dy³⁺ ions at different concentrations (x?=?0.03, 0.05, 0.07, 0.09 and 0.11) were determined to be about 0.855, 0.759, 0.686, 0.606 and 0.546 ms, respectively. The thermal stability of luminescence of Sr₃YNa(PO₄)₃F:0.07Dy³⁺ phosphor was also investigated and the activated energy was deduced to be 0.228 eV, which shows good thermal stability. The chromaticity coordinates fall in the white-light region calculated by the emission spectrum. These results show that Sr₃YNa(PO₄)₃F:Dy³⁺ phosphor can be a promising white emitting phosphor for white LEDs.     

Nano Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Induced Fluxoid Jumps and Low Field Enhanced Critical Current Density in MgB<Subscript>2</Subscript> Superconductor

Nano particle of Fe₃O₄ (nFe₃O₄) up to 6 at% were doped in the superconducting MgB₂ samples. Despite the strong ferromagnetic nature of Fe₃O₄, both the ac susceptibility and the resistivity measurements show that up to 4 at% of Fe₃O₄, T _c =38 K is not changed, whereas for 6% T _c decreases by 6 K. This indicates that a low concentration of Fe does not substitute either the Mg or B sites and probably occupies the intergrain spaces. For 0.5% doped Fe₃O₄, an increase in J _c with respect to the pure MgB₂ samples is observed in the lower field and temperature regions (H<2 T and 20 K) indicating an enhanced flux pinning and the magnetic activation, i.e., the interaction between the magnetic dipole of Fe ion and the vortices is weak in comparison to the effective pinning potential. Whereas, at H>2 T, J _c of the doped samples is always less than that of MgB₂, and the activation is dominant in comparison with the effective pinning potential provided by the doping. Flux jumps are observed in lower T and H regions for the samples doped up to 1% nFe₃O₄ only. Magnetization plots of higher Fe content samples exhibited clear paramagnetic background. Mossbauer measurements for the higher (4, 6 at%) nFe₃O₄ doped MgB₂ samples show that at RT, the hyperfine field for both samples is ∼100 kOe and ∼120 kOe at 90 K. This means that the nFe₃O₄ particles decompose and form possibly an intermetallic Fe-B phase in the matrix.     

X-ray diffraction studies of NbTe<Subscript>2</Subscript> single crystal

NbTe₂ is a member of transition metal dichalcogenide (TMDC) group. Single crystals of niobium ditelluride (NbTe₂) have been grown by a chemical vapour transport technique using iodine as transporting agent. The composition of the grown crystals was confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray diffraction (XRD) studies. Lattice parameters, volume and X-ray density have been carried out for the grown crystals. The particle size for a number of reflections has been calculated using Scherrer’s formula.