Spectroscopy and Structure of Nd<Superscript>3+</Superscript> Activator Centers in Stabilized Cubic ZrO<Subscript>2</Subscript>

The nonuniformly broadened spectra of Nd³⁺ in ZrO₂-Y₂O₃-Nd₂O₃ crystals are studied using selective excitation, different time delays, and measurements of the excited-state lifetime at 77 K. Three basic types of optical spectra are identified and are assigned to three basic configurations of the nearest neighbor environment of Nd³⁺: sevenfold coordination and eightfold coordination with and without an oxygen vacancy among its second neighbors.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 8, 2005, pp. 955–959.Original Russian Text Copyright © 2005 by Voron’ko, Lomonova, Popov, Sobol’, Ushakov.     

Morphology and luminescent properties of Al<Superscript>3+</Superscript>/Mg<Superscript>2+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor

Al³⁺/Mg²⁺ doped Y₂O₃:Eu phosphor was synthesized by the glycine-nitrate solution combustion method. In contrast to Y₂O₃:Eu which showed an irregular shape of agglomerated particles (the mean particle size >10 μm), the morphology of Al³⁺/Mg²⁺ doped Y₂O₃:Eu crystals was quite regular. Al³⁺/Mg²⁺ substituting Y³⁺ in Y₂O₃:Eu resulted in an obvious decrease of the particle size. Meanwhile, higher the Al³⁺/Mg²⁺ concentration, smaller the particle size. In particular, the introduction of Al³⁺ ion into Y₂O₃ lattice induced a remarkable increase of PL and CL intensity. While, for Mg²⁺ doped Y₂O₃:Eu samples, their PL and CL intensities decreased. The reason that causes the variation of PL and CL properties for Al³⁺ and Mg²⁺ doped Y₂O₃:Eu crystals was concluded to be related to sites of Al³⁺ and Mg²⁺ ions inclined to take and the difference of ion charge.     

Synthesis and properties of laser-active liquids POCl<Subscript>3</Subscript>-SbCl<Subscript>5</Subscript>-<Superscript>235</Superscript>UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack>-Nd<Superscript>3+</Superscript>

The effect of the synthesis conditions on the properties of inorganic laser-active liquids POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ -Nd³⁺ is considered. The kinetic dependences of the U(IV) content and decay time of the Nd³⁺ luminescence in POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions for various synthesis procedures at 380 K have been obtained. In POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions, nonradiative energy transfer Nd³⁺ → U⁴⁺ is observed, and quenching of the Nd³⁺ luminescence is described by the Stern-Volmer law: k _q = (6.4 ± 0.6) × 10⁵ l mol^?1 s^?1. Laser liquids POCl₃-SbCl₅-²³⁵UO ₂ ²⁺ -Nd³⁺ with neodymium concentration of up to 0.7 M, uranyl concentration of up to 0.1 M, and decay time of the Nd³⁺ luminescence of up to 220 μs have been prepared for the first time.     

Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> co-stabilized ZrO<Subscript>2</Subscript>-WC composites

Y₂O₃ + Nd₂O₃ co-stabilized ZrO₂-based composites with 40 vol% WC were fully densified by pulsed electric current sintering (PECS) at 1350 °C and 1450 °C. The influence of the PECS temperature and Nd₂O₃ co-stabilizer content on the densification, hardness, fracture toughness and bending strength of the composites was investigated. The best combination of properties was obtained for a 1 mol% Y₂O₃ and 0.75 mol% Nd₂O₃ co-stabilized composite densified for 2 min at 1450 °C under a pressure of 62 MPa, resulting in a hardness of 15.5 ± 0.2 GPa, an excellent toughness of 9.6 ± 0.4 MPa.m^0.5 and an impressive 3-point bending strength of 2.04 ± 0.08 GPa. The hydrothermal stability of the 1 mol% Y₂O₃ + 1 mol% Nd₂O₃ co-stabilized ZrO₂-WC (60/40) composites was compared with that of the equivalent 2 mol% Y₂O₃ stabilized ceramic. The double stabilized composite did not degrade in 1.5 MPa steam at 200 °C after 4000 min, whereas the yttria stabilized composite degraded after less than 2000 min. Moreover, the (1Y,1Nd) ZrO₂-WC composites have a substantially higher toughness (~9 MPa.m^0.5) than their 2Y stabilized equivalents (~7 MPa.m^0.5).     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.     

Roles of doping ions in persistent luminescence of SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, RE<Superscript>3+</Superscript> phosphors

The polycrystalline Eu²⁺ and RE³⁺ co-doped strontium aluminates SrAl₂O₄:Eu²⁺, RE³⁺ were prepared by solid state reactions. The UV-excited photoluminescence, persistent luminescence and thermo-luminescence of the SrAl₂O₄:Eu²⁺, RE³⁺ phosphors with different composition and doping ions were studied and compared. The results showed that the doped Eu²⁺ ion in SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors works as not only the UV-excited luminescent center but also the persistent luminescent center. The doped Dy³⁺ ion can hardly yield any luminescence under UV-excitation, but can form a electron trap with appropriate depth and greatly enhance the persistent luminescence and thermo-luminescence of SrAl₂O₄:Eu²⁺. Different co-doping RE³⁺ ions showed different effects on persistent luminescence. Only the RE³⁺ ion (e.g. Dy³⁺, Nd³⁺), which has a suitable optical electro-negativity, can form the appropriate electron trap and greatly improve the persistent luminescence of SrAl₂O₄:Eu²⁺. Based on above observations, a persistent luminescence mechanism, electron transfer model, was proposed and illustrated.     

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.     

Manifestation of Nd ions on the structure,Raman and IR spectra of (TeO<Subscript>2</Subscript>-MoO-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>) glasses

The structure of [80TeO₂ + (20–x)MoO + xNd₂O₃] glasses, with x = 0, 4, 6, 10 and 12 mol%, is studied in this work. Raman scattering in the spectral range (−2000 to 3500 cm⁻¹) and IR absorption spectra have been measured for crystalline TeO₂ and glasses, and their assignments were discussed and compared. Many vibrational modes were found active in both Raman and IR and their assignments for crystalline TeO₂ and for the glasses were discussed in relation to the tetragonal structure of crystalline α -TeO₂. Nd₂O₃ was found to completely eliminate diffuse scattering and enhance the Raman scattering intensity. Anti-stokes Raman bands in the range −1460 cm^{− 1} to −1975 cm^{− 1} were observed for both (30Li₂O + 70B₂O₃+ xNd₂O₃) glasses and [80TeO₂ + (20−x)MoO + xNd₂O₃] glasses and were attributed to some emission processes due to the doping of the glasses with Nd₂O₃.     

Relaxation of optical excitations in crystals of the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system with radiation defects

The photoluminescence and short-time persistence (afterglow) kinetics in pure and doped Y₂O₃-Al₂O₃ crystals excited with UV laser pulses (12 ns, 337 nm) were studied using samples irradiated with gamma quanta from a ⁶⁰Co source to a dose from 10⁴ to 10⁷ Gy. The relaxation time of the samples studied increases, with decreasing symmetry of the crystal lattice, in the following order: garnet—orthoaluminate—ruby—yttria. The afterglow duration and intensity significantly decrease in gamma-irradiated crystals, which is explained by the predominant recombination of close electron-hole pairs. Garnet-neodymium crystals are characterized by high radiation stability and fast relaxation kinetics.     

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     

Influence of Mg<Superscript>2+</Superscript>/Ga<Superscript>3+</Superscript> doping on luminescence of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphors

Mg²⁺/Ga³⁺ doped Y₃Al₅O₁₂:Ce³⁺ phosphors were synthesized through a solid state reaction. The phase and luminescent of the synthesized phosphors were investigated. For Ga³⁺ codoped Y_2.96Ce_0.04Al_(5?x)Ga_xO₁₂ phosphors, the emission intensity increases with the increase of Ga³⁺ concentration up to Y_2.96Ce_0.04Al_4.80Ga_0.20O₁₂ and then decreases with a further increase of Ga³⁺ concentration, but the emission peak shifts to shorter wavelength continuously in the Ga³⁺ doping concentration range of 0.05–0.25. For Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors, the emission intensity decreases and the emission peak shifts to longer wavelength continuously in the Mg²⁺ doping concentration range of 0.02–0.12. The emission spectra of Y_2.96Ce_0.04Al_(4.8?y)Ga_0.20Mg_yO₁₂ phosphors demonstrate that the codoped Mg²⁺/Ga³⁺ ions not only induce the enhancement of Y_2.96Ce_0.04Al₅O₁₂ emission intensity but also lead to the red shift of Y_2.96Ce_0.04Al₅O₁₂ emission peak. The decay lifetimes decrease in Mg²⁺/Ga³⁺ codoped Y_2.96Ce_0.04Al₅O₁₂ phosphors due to defects formed by substitutions of Y³⁺ by Mg²⁺/Ga³⁺.     

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.     

Magnetic properties of Nd-Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles

Nb³⁺-substituted garnet nanoparticles Y_3−xNd_xFe₅O₁₂ (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The XRD patterns of Y_3−xNd_xFe₅O₁₂ have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y_3−xNd_xFe₅O₁₂ increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y_3−xNd_xFe₅O₁₂, which leads to the decrease of the effective moment formed by Fe³⁺. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.     

Electrical Conductivity of Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> Crystals Doped with Ca<Superscript>2+</Superscript>, Pb<Superscript>2+</Superscript>, Sr<Superscript>2+</Superscript>, and Ba<Superscript>2+</Superscript>

Single crystals of Bi₂WO₆ (a layered perovskite-like compound) doped with Ca²⁺, Pb²⁺, Sr²⁺, and Ba²⁺ on the Bi³⁺ site are grown, and their oxygen ionic conductivity is measured along the polar axis. The intrinsic conductivity of the doped crystals differs insignificantly from the conductivity of undoped Bi₂WO₆, indicating that the oxygen ions in the Bi₂O₂ layers contribute little to the oxygen ionic conductivity of the crystals. The sharp change in the activation energy for conduction at 600°C attests to a transition from one conduction mechanism to another in going from low to high temperatures.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 863–865.Original Russian Text Copyright © 2005 by Kharitonova, Voronkova, Yanovskii.     

Oxidation of tungsten in the W-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system at temperatures from 2350 to 2500 K and pressures from 1 to 10<Superscript>5</Superscript> Pa

We examine chemical reactions that lead to the oxidation of tungsten in the W-Al₂O₃ system at T = 2350–2500 K and p = 1–10⁵ Pa. The results indicate that, for p ≥ 10 Pa, tungsten oxidizes through reactions with both Al₂O₃ vapor and dissociation products (Al₂O₂, Al₂O, AlO₂, and AlO). For p ≤ 10 Pa, oxidation is due to direct reaction of tungsten with O and/or O₂. For p ≤ 2 Pa, tungsten may react with molten Al₂O₃. A detailed analysis of tungsten oxidation processes is intended to optimize parameters of the melt growth of corundum crystals.     

Study of the effect of Li<Superscript>+</Superscript> concentration on the photoluminescence properties of Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphors

Y₂O₃:Eu³⁺ phosphors were prepared by hydrothermal method. Effect of the doping concentration of Eu³⁺ on the photoluminescence properties of Y₂O₃:Eu³⁺ phosphor was studied in details. It was found that the strongest emission intensity is achieved as atomic ratio of Y³⁺ to Eu³⁺ is 8. As concentration of Eu³⁺ exceeds the critical concentration, the emission intensity decreases dramatically due to the concentration quenching of Eu³⁺. Also, the effect of Li⁺ on the photoluminescence performance of the Y₂O₃:Eu³⁺ phosphor is studied in this work. According to the results, the doping of Li⁺ may greatly improve the PL performance of the Y₂O₃:Eu³⁺ phosphors due to the flux effect and improved crystallinity caused by the doping of Li⁺.     

Effect of Pr<Superscript>3+</Superscript> on the stokes luminescence of YPO<Subscript>4</Subscript>:Nd<Superscript>3+</Superscript> under IR excitation

We have identified general relationships between the spectral and kinetic properties of the IR Stokes luminescence bands of Y_{1 − x − y} Nd _x Pr _y PO₄ solid solutions in the spectral range 0.86–1.40 μm under 0.810-μm laser excitation. The results have been used to formulate technical requirements for the purity of rare-earth oxides for the fabrication of efficient YPO₄:Nd³⁺ IR phosphors and to develop a fast YPO₄:Nd³⁺, Pr³⁺ IR phosphor that allows the decay time of the Nd³⁺ IR Stokes luminescence bands in the range 0.86–1.40 μm to be tuned from 50 to 170 μs by varying the ratio of the Nd³⁺ and Pr³⁺ concentrations.     

Synthesis,tunable luminescence and thermal stability of Mg<Subscript>2</Subscript>Al<Subscript>4</Subscript>Si<Subscript>5</Subscript>O<Subscript>18</Subscript>:Ce<Superscript>3+</Superscript>/Mn<Superscript>2+</Superscript> phosphors

Ce³⁺/Mn²⁺ singly doped and codoped Mg₂Al₄Si₅O₁₈ phosphors were synthesized by a solid state reaction. The phase, luminescent properties and thermal stability of the synthesized phosphors were investigated. Ce³⁺ and Mn²⁺ singly doped Mg₂Al₄Si₅O₁₈ phosphors show emission bands locating in blue and yellow–red regions, respectively. In Ce³⁺ and Mn²⁺ codoped Mg₂Al₄Si₅O₁₈, tunable luminescence was obtained because of the energy transfer from Ce³⁺ to Mn²⁺. In Mg₂Al₄Si₅O₁₈:Ce³⁺/Mn²⁺ phosphors with a fixed Ce³⁺ concentration, energy transfer efficiency increases with the increasing Mn²⁺ concentration, which is confirmed by the continually decreasing intensity and shortening decay time of Ce³⁺ emission. Moreover, the luminescent properties and thermal stability provide a great significance on the applications in the field of light emitting diodes.     

Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> system

Polycrystalline samples of Ba₄Ln₂Fe₂Ta₈O₃₀ (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelectrics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stability, a relatively small temperature coefficient of dielectric constant (τ _ε ) of −25 and −58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 × 10⁻³ and 2.8 × 10⁻³ (at 1 MHz) for Ba₄La₂Fe₂Ta₈O₃₀ and Ba₄Nd₂Fe₂Ta₈O₃₀, respectively. The measured dielectric properties indicate that both materials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology.     

Comparative crystal field calculations of the Cr<Superscript>3+</Superscript> energy level schemes in ZnAl<Subscript>2</Subscript>S<Subscript>4</Subscript> and ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript>

The exchange charge model of crystal field (which includes the covalent effects) is used to analyze the energy level schemes of Cr³⁺ ion in ZnAl₂S₄ and ZnGa₂O₄ crystals with spinel structure. Calculations of the overlap integrals and crystal field parameters were performed before getting the Cr³⁺ energy levels. The calculated energy level schemes are compared with available experimental data; a new interpretation of the absorption peaks is suggested.