Growth and characterization of Nd,Yb – yttrium oxide nanopowders obtained by sol‐gel method

Nanopowders of Y₂O₃ pure, doped and codoped by Nd³⁺, Yb³⁺ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y₂O₃ doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y₂O₃ doped 0.5 at% Nd and 2 at% Yb are presented. Y₂O₃ containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Luminescence characteristics of undoped and Eu‐doped GdCa4O(BO3)3 single crystals and nanopowders

Single crystals of GdCa₄O(BO₃)₃ (GdCOB) pure and doped with Eu concentration of 1 and 4 at% were grown by the Czochralski and micropulling‐down methods. The distribution of Eu ions in GdCOB crystals was uniform. The substitutions of Eu³⁺ in Gd, Ca(1) and Ca(2) cation sites and eventually formation Eu²⁺ have been investigated. The spectroscopic properties of crystals are compared with the properties of nanopowders obtained by sol‐gel method. Radioluminescence spectra of undoped GdCOB crystal show the characteristic emission of Gd³⁺ at about 312 nm, whereas this emission dramatically decreases in Eu‐doped crystals upon X‐ray excitation, as well as in Eu‐doped nanopowders excited in vacuum ultraviolet (VUV) region. The VUV excitation in the range 125‐333 nm for Eu‐doped samples leads to strong emission in red coming from the ⁵D₀ multiplet of Eu³⁺, only. In the photoluminescence decay kinetics of 312 nm emissions substantial shortening and departure for single exponential decay in Eu‐doped samples is clearly observed. Higher Eu doping results in further acceleration of the decay. In undoped GdCOB crystal, the lifetime of the Gd^{3+ 6}P_7/2 multiplet is 2.79 ms. The Eu^{3+ 5}D₀ decay kinetics monitored at 613 nm are rather constant. Numerical fitting of fully exponential curves, reveals lifetimes 2.7 ms for nanopowder and 2.5 ms for single crystal. The results suggest that this material may be used as a red phosphor in plasma display panels in nanopowder form because of strong excitation band of Eu³⁺ luminescence in the 160‐200 nm regions. Contrary to nanopowder sample, such an excitation band, attributed to the Gd³⁺–O^2– charge transfer was not observed in crystal obtained by the micropulling‐down method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect structure and light‐induced scattering of Zr‐doped near‐stoichiometric Mn:Fe:LiNbO3 crystals grown by TSSG method

Near‐stoichiometric Mn:Fe:LiNbO₃ crystals doped with various concentration of ZrO₂ were grown by top seed solution growth (TSSG) method in the air atmosphere. The Zr concentration in the crystal was determined by inductively coupled plasma optical emission spectrometer. The defect structures were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of vibration peak at 3466 cm^‐1 in infrared spectra manifested that Li/Nb ratio in crystals approached to stoichiometric proportion. The fundamental absorption edge represented continuous red‐shift which was discrepancy with congruent doped LiNbO₃ crystals showed that doping ions possessed different location mechanism. The light‐induced scattering of the doped stoichiometric LiNbO₃crystals were quantitatively scaled via incident exposure energy. The results demonstrated that Zr(2 mol%):Mn:Fe:LiNbO₃ crystal had the weakest light‐induced scattering and the mechanism related to their defect structures was discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of pure and doped nonlinear optical l‐arginine acetate single crystals

Single crystals of organic nonlinear optical material of pure, Cu²⁺ and Mg²⁺ doped L‐arginine acetate (LAA) were successfully grown by slow evaporation method at room temperature. The UV‐Vis‐NIR spectra of pure and doped LAA indicate that these crystals possess a wide optical transmission window from 240‐1600 nm. Non‐linear optical studies reveal that the SHG efficiency of LAA is nearly three times that of KDP. The dielectric response of the samples was studied in the frequency region 100 Hz to 2 MHz and the influence of Cu²⁺ and Mg²⁺ substitution on the dielectric behaviour had been investigated. Photoconductivity study proves that both pure and Cu²⁺ and Mg²⁺ doped LAA crystal exhibit positive photoconductivity. It is evident from the Vickers hardness study that the hardness of the crystal decreases with increasing load both for pure and doped samples. ESR studies confirmed the incorporation of Cu²⁺ into LAA and the value of g‐factor was found to be 2.1654. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Homoepitaxial growth and photoluminescence of self‐assembled In‐doped ZnS nanowire bundles

Self‐assembled In (Indium)‐doped ZnS nanowire bundles were synthesized via a thermal evaporation method without using any template. Vapor ‐ solid homoepitaxial growth was found to be the key reason for the formation of close‐packed nanowire bundles grown on the surface of microscale sphere‐shaped ZnS crystal. X‐ray diffraction (XRD), selected area electron diffraction (SAED), and transmission electron microscopy (TEM) analysis demonstrate that the In‐doped ZnS nanowires have the cubic structure, and there are numerous stacking faults along the <111> direction. Photoluminescence (PL) spectrum shows that the spectrum mainly includes two parts: a weak violet emission band centering at about 380 nm and a strong green emission band centering at about 510 nm. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improved blue photorefractive properties of near‐stoichiometric LiNbO3:Mn:Fe:Zr crystal

Near‐stoichiometric LiNbO₃ single crystal tri‐doped with ZrO₂, MnO and Fe₂O₃ was grown from Li‐riched melt by Czochralski method. The defect structures and composition of these crystals were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of 3466 cm^‐1 peak in infrared spectra showed that the crystal grown from Li‐riched melt was near stoichiometric. The photorefractive properties at the wavelength of 488 nm and 633 nm were investigated with two‐beam coupling experiment, respectively. The experimental results showed that the response speed and sensitivity were enhanced significantly and the high diffraction efficiency was obtained at 488 nm wavelength. This manifested that near‐stoichiometric LiNbO₃:Mn:Fe:Zr crystal was an excellent candidate for holographic storage. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Micro‐Pulling Down Growth of Co‐doped Lithium Niobate Single Crystal Fibers According Er and Mg Contents and Photolumenescence Properties

The Er³⁺doped Mg:LiNbO₃single crystal fibers employed in our experiment were grown in air by a micro‐pulling down (μ‐PD) method from host materials of a congruent Li/Nb (0.945) ratio which were melt‐doped with a nominal molar concentration of 1, 3, 5% MgO and 0.6% Er₂O₃. The X‐ray diffraction analysis results indicated that the co‐doped crystals main tained the same structural characteristics as the undoped LiNbO₃, however the lattice parameters with Mg differed; c (Å) value decreased, and a (Å) increased than of pure LiNbO₃. The influence of dopants on the photoluminescence (PL) properties of the Er:Mg:LiNbO₃ single crystal fibers excited by laser lines of 514 nm was reported. Also, the PL properties according to temperature and the excitation power of Er:Mg:LiNbO₃ crystal fibers were analyzed.     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

Structural and optical response of 2‐Mercaptoethonal capped CdS nanocrystals to Fe3+ ions

Cadmium sulfide (CdS) semiconductor nanocrystals (NCs) doped with Fe³⁺ have been synthesized via a solution‐based method utilizing dopant concentrations of (0–5%) and employing 2‐mercaptoehonal as a capping agent. X‐ray diffraction (XRD) results showed that the undoped CdS NCs are in mixed phase of cubic and hexagonal, where as the doped CdS NCs are in hexagonal phase. The crystallite size was increased from ∼1.2 nm to ∼2 nm. Diffuse reflectance spectroscopy studies (DRS) reveals that the band gap energy was decreased with Fe doping and it lies in the range of 2.58 ‐ 2.88 eV. Photoluminescence (PL) spectra of undoped CdS NCs show a strong green emission peak centered at 530 nm and a weak red emission shoulder positioned at 580 nm. After doping all the luminescence intensity was highly quenched and the green emission peak was shifted to orange region (580 nm), but the position of weak red emission shoulder was unaltered with doping. FTIR studies revealed that the NCs were sterically stabilized by 2‐mercaptoethanol. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Properties of Sm‐doped CaNb2O6 thin films deposited by radio‐frequency magnetron sputtering

Sm‐doped CaNb₂O₆ (CaNb₂O₆:Sm) phosphor thin films were prepared by radio‐frequency magnetron sputtering on sapphire substrates. The thin films were grown at several growth temperatures and subsequently annealed at 800 °C in air. The crystallinity, surface morphology, optical transmittance, and photoluminescence of the thin films were investigated by X‐ray diffraction, scanning electron microscopy, ultraviolet‐visible spectrophotometry, and fluorescence spectrophotometry, respectively. All of the thin films showed a main red emission radiated by the transition from the ⁴G_5/2 excited state to the ⁶H_9/2 ground state of the Sm³⁺ ions and several weak bands under ultraviolet excitation with a 279 nm wavelength. The optimum growth temperature for depositing the high‐quality CaNb₂O₆:Sm thin films, which was determined from the luminescence intensity, was found to be 400 °C, where the thin film exhibited an orthorhombic structure with a thickness of 370 nm, an average grain size of 220 nm, a band gap energy of 3.99 eV, and an average optical transmittance of 85.9%. These results indicate that the growth temperature plays an important role in controlling the emission intensity and optical band gap energy of CaNb₂O₆:Sm thin films.     

Optical Parameters of Nd‐Doped Gadolinium Aluminium Tetraborate Crystals

Nd‐doped gadolinium aluminium tetraborate, Nd_xGd_1‐xAl₃(BO₃)₄ (NGAB), crystallizes with x = 0.1 in the trigonal system with point group 32, conforming space group R32. They were grown using flux method, of large sizes and good optical quality. The unit cell constants were a = 0.93057 (6) and c = 0.72481 (3) nm, and z = 1. The measured absorption of the NGAB is compared to Judd‐Ofelt (JO) theory. When applied, the JO theory of parity‐forbidden electric‐dipole transitions of rare earth ions on noncentrosymmetric sites demonstrates good agreement. A measured band gap of the eigentransition was about 4.00 eV. The fitted intensity parameters Ot (t = 2, 4, and 6) were 2.446 × 10^‐20, 2.266 × 10^‐20 and 2.598 × 10^‐20 cm². Both the emission properties of the sub‐stable ⁴F_3/2 state with the level lifetime of 506.20 μs and a fluorescence spectrum corresponding to the transition ⁴F_3/2 → ⁴I_11/2 were studied. The results indicate the pass band of laser for potential applications in practice.     

Growth and magneto‐optical characteristics of cerium‐doped terbium gallium garnet by the floating zone method

Cerium‐doped terbium gallium garnet single crystal having a large Verdet constant was grown by floating zone (FZ) method, which was suitable for the use in optical devices. The lattice parameters and the X‐ray rocking curve measurement of the crystal was determined by X‐ray diffraction analysis. The Verdet constant of the crystal (B = 0.55 T) at the wavelength of 632.8 nm was −165.8 rad m⁻¹ T⁻¹ at room temperature, 23.7% larger than that of pure TGG (−134.0 rad m⁻¹ T⁻¹). The performance of the high optical quality and excellent magneto‐optical properties of the crystal shows the great potential of using this new method to meet the increasing demand of VI‐NIR Faraday rotators.     

Preparation and characterization of Nd doped gadolinium gallium garnet nanopowders and crystals

The structural and optical features of gallium gadolinium garnet (GGG) nanopowders doped with neodymium were investigated. Nanopowders of GGG:Nd were prepared by modified sol‐gel method using acetic acid as complexing agent. This way permitted to incorporate large amounts of dopant (up to 10 %) without destroying garnet structure. Small single crystals of Nd:GGG were grown by a μ‐pulling down method and spectroscopic features of nanopowders and their single crystal counterparts were compared. It has concluded that the Nd³⁺ ions are located preferentially in the same type of sites in crystal lattices of GGG:Nd nanopowders and their single crystal counterparts. In addition, it follows from the perfect agreement of emission wavelengths and line width recorded for nanopowders and single crystal samples that the crystal lattice of GGG in nanopowders is not distorted. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Flux growth and characterization of Ti‐ and Ni‐doped forsterite single crystals

Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO₃, V₂O₅, Li₂CO₃) and nutrient was slowly cooled down to 750 °C from 1250 °C or 1350 °C. The crystals were then characterized by powder and single‐crystal X‐ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h^‐1. These synthetic, well‐characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and morphological studies on Mn substituted ZnO nanometer‐sized crystals

Mn substituted ZnO nanocrystals synthesized by a co‐precipitation method. X‐ray diffraction (XRD) studies confirms the presence of wurtzite (hexagonal) crystal structure similar to un doped ZnO, suggesting that doped Mn ions go at the regular Zn sites. The lattice parameters a and c are increasing with increasing Mn content. The unit cell volume increases with increasing Mn concentration, indicating the homogeneous substitution of Mn²⁺ for the Zn²⁺. The lattice distortion parameter (ε_v) is evaluated from XRD data and found that it enhances as Mn content increases. Transmission electron microscopy photographs show that the size of the ZnO crystals is in the range of 20‐50 nm. The SAED pattern confirms the hexagonal and crystalline nature of the samples which are in agreement with X‐ray analysis. The chemical groups of the samples have been identified by FTIR studies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and spectroscopic investigation of Yb/Nd co‐doped KLu(WO4)2 laser crystals

Single crystals of Yb, Nd: KLu(WO₄)₂ (Yb, Nd: KLW) of dimensions up to 40mm× 40mm×5mm have been grown by top‐seeded solution growth (TSSG) method. X‐ray powder diffraction pattern was measured and compared with that of Nd: KLuW and Yb: KLuW. Absorption and fluorescence spectra were measured at room temperature. The Judd‐Ofelt theory was applied to analyze the spectrum of Nd, Yb: KLuW crystal. The intensity parameters Ω_t (t=2, 4 and 6) were calculated as Ω₂=20.68×10^‐20cm², Ω₄=11.04×10^‐20cm², Ω₆=6.74×10^‐20cm² respectively, with a root mean square deviation of 0.58×10^‐20 cm². (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and downconversion luminescence of Ho3+/Yb3+ codoped α‐NaYF4 single crystals by the Bridgman method using a KF flux

Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448‐nm light in Ho³⁺/Yb³⁺ codoped α‐NaYF₄ single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF‐YF₃ system. The energy‐transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy‐transfer processes of first‐ and second‐order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first‐order cooperative DC that is dominant for the DC process. When the Ho³⁺ concentration is fixed at about 0.8 mol%, the optimal concentration for ∼1000 nm emission is 3.02 mol% Yb³⁺ in the current research. The energy‐transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in α‐NaYF₄ single crystals of 0.799 mol% Ho³⁺ and 15.15 mol% Yb³⁺. However, the emission intensity at 1000 nm decreases while the energy‐transfer efficiency from Ho³⁺ to Yb³⁺ increases, which may result from the fluorescence quenching between Ho³⁺ and Yb³⁺ ions, Yb³⁺ and Yb³⁺ ions.     

Studies on the growth and optical characterization of Tm3+‐doped BaY2F8 single crystals

The BaY₂F₈ crystals doped with different concentrations of Tm³⁺ ions were prepared by the temperature gradient technique (TGT). X‐ray powder diffraction was applied to analyze the phase. The cracking phenomenon along (010) and (100) planes of the crystals grown by temperature gradient technique was studied on the basis of the structure of BaY₂F₈ crystals. The absorption spectra were measured and investigated in the ultraviolet‐visible and near‐infrared ranges at room temperature. Several characteristic absorption bands of Tm³⁺‐doped BaY₂F₈ crystal were observed. The emission and excitation spectra were obtained and investigated at room temperature and 12 K, showing the characteristic emission peaks of Tm³⁺ ions. The temperature dependence of Photoluminescence curve was also investigated in the range of 12–296 K. The luminescence intensity of emission bands decreased with increasing temperature, while the effective bandwidth increased. The up‐conversion spectrum excited at 650 nm was recorded and up‐conversion mechanism was analyzed in detail. The result showed the purple, green and yellow emissions corresponding to ³P₁→³F₃, ¹D₂→³H₅ and ³P₀→¹G₄ transitions, respectively.     

UV‐visible emission of (O2‐ ‐ F+) centres in KBr

Single crystals of KBr containing the (O^2‐ ‐ F⁺) color centres and elaborated in atmospheric air by the Czochralski method are studied. The measure of the UV‐visible emission spectra at 78 K present several emission bands situated between 340 and 800 nm. The photoluminescence excitation shows that these emissions are attributed to O^‐₂ and (O^2‐ ‐ F⁺) centres. This study show the new emission bands of (O^2‐ ‐ F⁺) centres which are situated in the UV‐visible spectral domain. The comparison between the emission spectra before and after the thermal treatment of samples shows clearly the transformation of O^‐₂ centers at high temperature to (O^2‐ ‐ F⁺) centres. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and spectral properties of Nd:Ca5(BO3)3F

A neodymium doped Ca₅(BO₃)₃F single crystal with size up to 51×48×8 mm³ has been grown by the top seeded solution growth (TSSG) technique with a Li₂O‐B₂O₃‐LiF flux. The spectra of absorption and fluorescence were measured at room temperature. According to Judd‐Ofelt (J‐O) theory, the spectroscopic parameters were calculated and the J‐O parameters Ω₂, Ω₄, Ω₆ were obtained as follows: Ω₂ = 1.41×10⁻²⁰cm², Ω₄ = 3.18×10⁻²⁰cm², Ω₆ = 2.11×10⁻²⁰cm². The room temperature fluorescence lifetime of NCBF was measured to be 51.8 μs. According to the J‐O paramenters, the emission probabilities of transitions, branching ratios, the radiative lifetime and the quantum efficiency from the Nd^{3+ 4}F_3/2 metastable state to lower lying J manifolds were also obtained. In comparasion with other Nd‐doped borate crystals, the calculated and experimental parameters show that NCBF is a promising SFD crystal.