Growth and spectroscopic properties of Nd-doped Na2Gd4(MoO4)7 crystal

This paper reports the growth and spectral properties of Nd³⁺:Na₂Gd₄(MoO₄)₇ crystals. An Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal with dimensions of Ø20 × 25 mm³ has been grown by the Czochralski method. The spectroscopic properties of Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The polarized absorption cross-sections of Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal are 4.25 × 10⁻²⁰ cm² with full width at half maximum (FWHM) of 14.6 nm for the π-polarization and 2.87 × 10⁻²⁰ cm² with FWHM of 16.2 nm for the σ-polarization, respectively. The emission cross-sections are 10.0 × 10⁻²⁰ cm² at 1060 nm for π-polarization and 13.6 × 10⁻²⁰ cm² at 1067 nm for σ-polarization, respectively. The fluorescence quantum efficiency has been estimated to be 90.0%. Nd³⁺:Na₂Gd₄(MoO₄)₇ crystal may be considered as a potential laser gain medium for the diode laser pumping.     

Structural, dielectric and magnetic properties of Nd-doped Co2Z-type hexaferrites

Z-type hexaferrites doped with Nd³⁺, Ba_3−xNd_xCo₂Fe₂₄O₄₁ (x = 0, 0.05, 0.10, 0.15, and 0.25), were prepared by solid-state reaction. The effect of the Nd³⁺ ions substitution for Ba²⁺ ions on the microstructure and electromagnetic properties of the samples was investigated. The results reveal that an important modification of microstructure, complex permeability, complex permittivity, and static magnetic properties can be obtained by introducing a relatively small amount of Nd³⁺ instead of Ba²⁺. SEM image shows that the grains of the ferrites doped with Nd³⁺ were smaller, more perfect and homogeneous than that of the pure ferrite. The real part (?′) of complex permittivity and imaginary part (?″) increase at first, and then decrease with increasing Nd content. At low frequency, the imaginary part μ″ of complex permeability decreases with Nd content and then increases when frequency is above 7.0 GHz. The magnetization (M_s) and the coercivity (H_c) are 79.38 emu g⁻¹ and 36.94 Oe for Ba_2.75Nd_0.25Co₂Fe₂₄O₄₁. The data of magnetism show that the ferrite doped with Nd³⁺ ions is a better soft magnetic material due to the higher magnetization and lower coercivity.     

Preparation, structure and photoluminescence of nanoscaled-Nd: Lu3Al5O12

Nd:Lu₃Al₅O₁₂ (Nd:LuAG) nano-crystalline was synthesized by co-precipitation method. Its phase transformation, structure, absorption and photoluminescence properties were studied. The Nd:LuAG polycrystalline phase is formed above 900 °C and its particle sizes are in the range of 18-36 nm. The structure of Nd:LuAG was refined by Rietveld method. The lattice parameters and the distortion of Lu³⁺-O²⁻ polyhedron in Nd:LuAG are larger than that of in pure LuAG. Because the distortion of Lu³⁺-O²⁻ polyhedron is larger than that of Y³⁺-O²⁻ polyhedron in YAG and the distance of Lu³⁺-O²⁻ is smaller than that of Y³⁺-O²⁻ in YAG, Nd³⁺ in LuAG experiences a stronger crystal field effect, which is proved by the crystal field strength and the chemical environment parameter. The absorption spectrum shows that Nd:LuAG has a broad absorption band at 808 nm with FWHM above 6 nm, which is favorable for improving laser efficiency. The fluorescence lifetime from ⁴F_3/2 → ⁴I_11/2 transition is 320 μs and longer than that of Nd:YAG. The longer lifetime is propitious to energy storage. The emission cross section at 1064 nm is 2.89 × 10⁻¹⁹ cm², taking into account the Boltzmann distribution of the excited state. The emission cross section in Nd:LuAG is also larger than that of Nd:YAG, which is useful for laser operation. All results indicate that Nd:LuAG is a promising crystal material to apply in high energy lasers.     

Influence of the Nd3+ ions content on the FTIR and the visible up-conversion luminescence properties of nano-structure BaTiO3, prepared by sol–gel technique

The nano-structure BaTiO₃ (BT) powder doped with different concentrations of Nd³⁺ ions were annealed at 750 °C for 1 h to form nano-structure tetragonal phase of BT powder. The structure properties studied using XRD and FTIR methods. Sensitized up-conversion luminescence observed under excitation of 808 nm diode laser, suggesting that the Nd³⁺ ions-doped BT might be an ideal up-conversion material for infrared excitation. The influence of increasing the concentration of the Nd³⁺ ions on the luminescence intensity investigated using laser diode. The up-conversion mechanisms in the doped system will be discussed by analyzing the energy level structures of the Nd³⁺ ions.     

Effective segregation during Czochralski growth and spectral properties of Nd in GSAG crystal

GSAG and Nd:GSAG crystals were grown by standard Czochralski technique. The refractive index of GSAG in the wavelength range 500-3000 nm, effective segregation coefficient and absorption cross sections of Nd³⁺ in GSAG were determined by optical absorption method. The effective segregation coefficient was calculated to be 0.525. The spectroscopic and laser properties of Nd:GSAG crystal were studied by Judd-Ofelt analysis. The Judd-Ofelt parameters were calculated to be Ω₂ = 1.32 × 10⁻²¹ cm², Ω₄ = 2.93 × 10⁻²⁰ cm² and Ω₆ = 3.91 × 10⁻²⁰ cm². With these intensity parameters, the values of absorption and emission oscillator strengths, transition probabilities, fluorescence ratios and radiative lifetimes were obtained. The large fluorescence ratio of |[4F]3/2〉 is very favorable for laser operation at 942 nm. These results confirm that Nd:GSAG is a suitable laser material for water vapor detection by DIAL.     

Sorption of Hg<Superscript>2+</Superscript>, Nd<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>, and Uo<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> ions at polysiloxane xerogels functionalized with phosphonic acid derivatives

The sorption properties of silicas with mono- and bifunctional surface layers containing the complexing fragment ≡Si(CH₂)₃NHP(S)(OC₂H₅)₂ were studied. It was found that xerogels synthesized by the solgel method (like mesoporous silicas obtained by the template method) can extract mercury(II) ions from acidified solutions (SSC up to 450 mg/g). In a nonporous xerogel with a bifunctional surface layer (≡P=S/-SH), thiol groups proved to be primary sorption sites for Hg²⁺ ions; part of the ligand groups were inaccessible to metal ions. Xerogels containing the phosphonic acid residues ≡Si(CH₂)₂P(O)(OH)₂ sorbed uranyl and lanthanide ions from their nitrate solutions. The resulting surface complexes contained two (for the UO ₂ ²⁺ ion) or three innersphere ligand groups (for the Nd³⁺ and Dy³⁺ ions). The maximum SSCs were 340 mg/g for the uranyl ion and 120 mg/g for the lanthanide ions.     

Concentration-dependent luminescence and energy transfer of flower-like Y2(MoO4)3:Dy phosphor

Flower-like Y₂(MoO₄)₃:Dy³⁺ phosphors have been synthesized via a co-precipitation approach with the aid of β-cyclodextrin. The crystal structure and morphology of the phosphors were characterized by XRD (X-ray diffraction) and FE-SEM (field emission scanning electron microscopy), respectively. The excitation and emission properties of the phosphors were examined by fluorescence spectroscopy. The dependence of color coordinates on the Dy³⁺ doping concentration was analyzed. The energy transfer mechanism between Dy³⁺ ions was studied based on the Huang's theory, I-H and Van Uitert's models. It was concluded simultaneously from these three routes that the electric dipole-dipole interaction between Dy³⁺ ions is the main physical mechanism for the energy transfers between Dy³⁺.     

Structure,dielectric and optical properties of Nd3+-doped LiTaO3 transparent ferroelectric glass–ceramic nanocomposites

Here, we present the structural, dielectric and optical properties of neodymium ion (Nd³⁺) doped novel transparent glass-ceramics containing LiTaO₃ nanocrystals in the Li₂O–Ta₂O₅–SiO₂–Al₂O₃ (LTSA) glass system prepared by the melt-quenching technique. The precursor glasses were isothermally crystallized at 680 °C for 3–100 h, following the differential thermal analysis (DTA) data, to obtain nanostructured glass-ceramics. They were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Fourier transform infrared reflection spectra (FTIRRS), optical absorption and luminescence spectroscopy along with dielectric constant measurements. XRD, FESEM, TEM and FTIRRS confirm the nanocrystallization of LiTaO₃ (14–36 nm) in the LTSA glass matrix. A steep increase in dielectric constant (?_r) of glass-ceramics with heat-treatment time is observed due to high dielectric constant ferroelectric LiTaO₃ formation. The measured NIR photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 809 nm. It is observed that the photoluminescent intensity and excited state (⁴F_3/2) lifetime of Nd³⁺ ions decrease with increase in heat-treatment time due to concentration quenching effect. The absorption spectra and fluorescence measurements reveal that the incorporation of Nd³⁺ ions in the LiTaO₃ crystal lattice in the oxide glassy matrix is important for obtaining desirable fluorescence performance of the material.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Solubility of YAG:Nd in borate glass-luminescence and Raman investigation

YAG:Nd powders obtained by grinding a single crystal and synthesized by modified sol-gel and combustion methods were embedded at the stage of melting in a multicomponent borate glass to obtain luminescent glass-ceramic systems. Room temperature optical absorption spectra, luminescence spectra at room temperature and at 10 K and micro-Raman spectra were recorded to determine the location of Nd³⁺ ions in composite materials. It has been concluded that their luminescence characteristics depend critically on the preparation method hence the morphology of precursor crystalline YAG:Nd powders as a consequence of dissimilar solubility of crystallites in a host glass.     

Phase relations and optoelectronic characteristics in the NdVO4–BiVO4 system

Studies performed on the NdVO₄–BiVO₄ system showed the existence of the Bi_xNd_1?xVO₄ homogeneity range for x ? 0.49(1). Extended X-ray absorption fine structure and X-ray diffraction analyses confirmed that Bi³⁺ is incorporated onto the Nd site in the NdVO₄ crystal structure with some distortion of the local structure. Surprisingly, the unit cell volume decreases with the increase in the content of the larger Bi³⁺ ion. On the other side of the NdVO₄–BiVO₄ system, Nd³⁺ does not enter the BiVO₄ structure but forms the NdVO₄-based secondary phase. Ultraviolet–visible spectroscopy showed that the band gap of NdVO₄ can be reduced to below 3.1 eV by the Bi doping. New emissions that do not exist for NdVO₄ have been found in the 650–675 nm range of Bi_xNd_1?xVO₄ photoluminescence spectra. The observed chemical and optoelectronic properties were explained on the basis of the hybridization of Bi 6s² and O 2p orbitals.     

Sorption of Hg2+, Nd3+, Dy3+, and Uo 22+ ions at polysiloxane xerogels functionalized with phosphonic acid derivatives

The sorption properties of silicas with mono- and bifunctional surface layers containing the complexing fragment ≡Si(CH₂)₃NHP(S)(OC₂H₅)₂ were studied. It was found that xerogels synthesized by the solgel method (like mesoporous silicas obtained by the template method) can extract mercury(II) ions from acidified solutions (SSC up to 450 mg/g). In a nonporous xerogel with a bifunctional surface layer (≡P=S/-SH), thiol groups proved to be primary sorption sites for Hg²⁺ ions; part of the ligand groups were inaccessible to metal ions. Xerogels containing the phosphonic acid residues ≡Si(CH₂)₂P(O)(OH)₂ sorbed uranyl and lanthanide ions from their nitrate solutions. The resulting surface complexes contained two (for the UO₂²⁺ ion) or three innersphere ligand groups (for the Nd³⁺ and Dy³⁺ ions). The maximum SSCs were 340 mg/g for the uranyl ion and 120 mg/g for the lanthanide ions. Original Russian Text ? O.A. Dudarko, V.P. Goncharik, V.Ya. Semenii, Yu.L. Zub, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 2, pp. 207–212.     

Part II. Large scale applications of NixMn0.8−xMg0.2Fe2O4; 0.1 ≤ x ≤ 0.35 using laser irradiation

Ni_xMn_0.8−xMg_0.2Fe₂O₄; 0.1 ≤ x ≤ 0.35 was prepared by standard ceramic technique at sintering temperature 1200 °C using heating / cooling rate 4 °C/min. The samples were irradiated by Nd YAG pulsed laser with energy of the pulse 250 mJ. X-ray diffractograms reveal cubic spinel structure for all the samples before and after laser irradiation. After laser irradiation, better crystallinity was obtained in a form of an increase in the calculated crystal size. This increase was discussed as due to the change in the valence of some ions like Fe³⁺, Ni²⁺ and Mn²⁺. The conductivity of all the investigated samples decreases after laser irradiation and becomes temperature independent for a wider range than that before irradiation. This was ascribed to electron rearrangement after laser irradiation. Accordingly, these ferrites are recommended to be useful in electronic devices.     

Spectroscopic studies of KGd(WO4)2:Ho single crystals

Single crystals of KGd(WO₄)₂ doped with Ho³⁺ ions were grown by the top seeded solution growth method. Polarized room temperature absorption spectra were analyzed by means of the conventional Judd-Ofelt theory taking into account strong dependence of the host refractive index on the wavelength. In addition to the intensity parameters Ω₂, Ω₄, Ω₆, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. The transitions predicted by the phenomenological model as potential transitions for laser applications are discussed. Emission spectra in the green, red, and near-infrared spectral regions were recorded for different excitation wavelengths. Comparison with spectroscopic properties of Ho³⁺ ion in other crystals is discussed.     

Magnetomechanical properties of epoxy-bonded Sm1−xNdxFe1.55 (0 ≤ x ≤ 0.56) pseudo-1-3 magnetostrictive particulate composites

Pseudo-1-3 magnetostrictive particulate composites consisting of light rare earth (Sm and Nd)-based magnetostrictive Sm_1−xNd_xFe_1.55 particles with the Nd content x of 0-0.56 and randomly distributed sizes of 10-180 μm embedded and aligned in a passive epoxy matrix are fabricated using the particulate volume fraction of 0.5. The quasistatic magnetomechanical properties of the composites are investigated and the results are compared with their monolithic alloys for various x. The composites exhibit similar qualitative trends in properties with the alloys for all x. The Sm_0.92Nd_0.08Fe_1.55 composite shows a large unsaturated magnetostriction λ of −530 ppm at 500 kA/m and a high piezomagnetic coefficient d₃₃ of −2.0 nm/A at 100 kA/m as a result of the magnetocrystalline anisotropy compensation between Sm³⁺ and Nd³⁺ ions in the Sm_0.92Nd_0.08Fe_1.55 alloy.     

Influence of La and Dy on the properties of the long afterglow phosphor CaAl2O4: Eu, Nd

The long afterglow phosphor CaAl₂O₄:Eu²⁺,Nd³⁺ was prepared by the high temperature solid-state reaction method, and the influence of La³⁺ and Dy³⁺ on the properties of the long afterglow phosphor was studied by X-ray diffraction (XRD), photoluminescence (PL), and thermoluminescence (TL). The XRD pattern shows the host phase of CaAl₂O₄ is produced and no impurity phase appears. The peak wavelength of the phosphor does not vary with La³⁺ and Dy³⁺ doping. It implies that the crystal field, which affects the 5d electron states of Eu²⁺, is not changed dramatically after doping of La³⁺ and Dy³⁺. The TL spectra indicate that the phosphor doped with La³⁺ or Dy³⁺ produces different depths of trap energy level. In the mechanism of long afterglow luminescence, it is considered that La³⁺ or Dy³⁺ works as trap energy level. The decay time lies on the number of electrons in the trap energy level and the rate of the electrons returning to the excitation level.     

Fluorescence and Judd–Ofelt analysis of Nd doped P2O5–Na2O–K2O glass

Sodium potassium phosphate glass consisting different Nd₂O₃ concentrations have been prepared to study the effect of Nd³⁺ concentration on optical absorption and fluorescence properties. From the absorption spectra, Racah (E¹, E², E³), spin-orbit (ξ_4f) and configuration interaction (α) parameters are calculated and reported for all the Nd³⁺ doped glasses. Judd–Ofelt intensity parameters (Ω₂, Ω₄, Ω₆) are evaluated and these parameters are used to study the covalency as a function of Nd³⁺ concentration. Results show that covalency decreases with the increase of Nd³⁺ concentration. By using these three intensity parameters, total radiative transition probabilities (A_T), radiative lifetimes (τ_R), branching ratios (β) and integrated absorption cross-sections (Σ) have been computed for certain excited states of Nd³⁺ in these mixed alkali phosphate glasses for all the concentrations. From the fluorescence spectra, peak stimulated emission cross-sections (σ_p) have been calculated for the two transitions, ⁴G_7/2 → ⁴I_13/2 and ⁴G_7/2 → ⁴I_11/2 of Nd³⁺ in all these glass matrices. From the absorption spectra, the optical band gaps (E_opt) for both direct and indirect transitions have been obtained. All these spectroscopic parameters are compared for different Nd³⁺ concentrations. From these studies, a few transitions are identified for laser excitation among various transitions.     

Effect of Nd2O3 addition on the surface phase of TiO2 and photocatalytic activity studied by UV Raman spectroscopy

TiO₂ modified with Nd₂O₃ (Nd-TiO₂) nanoparticles were prepared by a co-precipitation method and utilized as the photocatalysts for the degradation of Rhodamine B (RhB). The influence of Nd₂O₃ on the bulk and surface phase, surface area, particle size, and optical response of TiO₂ was investigated by X-ray diffraction (XRD), UV Raman spectroscopy, transmission electron microscopy (TEM), BET, and UV-visible diffuse reflectance spectra. It is found that the crystalline phase and phase composition in the bulk and surface region of Nd-TiO₂ calcined at high temperatures can be tuned by changing the amount of Nd₂O₃. Based on the results from XPS, EDX, XRD, and UV Raman spectra, it is assumed that Nd³⁺ ions do not enter the TiO₂ lattice, but highly disperse onto the Nd-TiO₂ particle surface in the form of Nd₂O₃ crystallites. These crystallites inhibit the agglomeration, growth in crystal size, and anatase-to-rutile phase transformation of TiO₂. In the photocatalytic degradation of RhB reaction, Nd-TiO₂ nanoparticles with higher surface area and wider optical response are more reactive in case of the same surface anatase phase. When the mixed phases of anatase and rutile exist in the surface region of Nd-TiO₂, the synergetic effect over surface area and optical response is the important parameter which determines optimal photocatalytic activity.     

Luminescence properties of red-emitting Ca<Subscript>2</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles prepared by sol-gel method

A series of red-emitting Ca2-xAl2SiO7:xEu3+(x = 1 mol.%-10 mol.%) phosphors were synthesized by the sol-gel method.The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2Al2SiO7:Eu3+ phosphors were investigated.X-ray diffraction(XRD) profiles showed that all peaks could be attributed to the tetragonal Ca2Al2SiO7 phase when the sample was annealed at 1000℃.Scanning electron microscopy(SEM) micrographs indicate that the phosphors have an irregularly rounded morphology with particles of about 200 nm.Excitation spectra showed that the strong broad band at around 258 nm and weak sharp lines in 350-490 nm were attributed to the charge transfer band of Eu3+-O2-and f-f transitions within the 4f6 configuration of Eu3+ ions,respectively.Emission spectra implied that the red luminescence could be attributed to the transitions from the 5D0 excited level to the 7FJ(J = 0,1,2,3,4) levels of Eu3+ ions with the main electric dipole transition 5D0→7F2(618 and 620 nm),and Eu3+ ions prefer to occupy a lower symmetry site in the crystal lattice.Moreover,the photoluminescence(PL) intensity was strongly dependent on both the sintering temperature and doping concentration,and the highest PL intensity was observed at an Eu3+ concentration x = 7 mol.% after annealing at 1100℃.The obtained Ca2Al2SiO7:Eu3+ phosphor may have potential application for the red lamp phosphor.     

Spectroscopic analysis of Nd:Ca3Gd2(BO3)4 crystal and laser operating at 1.06 μm

Laser crystal Ca₃Gd₂(BO₃)₄ of high quality activated with Nd³⁺ has been grown successfully by Czochralski technique. The product was characterized by means of X-ray diffraction (XRD) powder investigation. The absorption spectra along a-, b- and c-axes were measured and investigated according to the Judd-Ofelt theory. The fluorescence properties were pursued and the factors influencing the fluorescence quantum efficiency were indicated. Xe lamp-pumped pulsed laser results were also obtained and the highest output power was up to 62 mJ.