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.     

Growth and characterization of Mn2+ doped calcium l‐tartrate crystals

Single crystals of Mn²⁺ doped calcium levo‐ tartrate tetrahydrate (CLTT) were grown by single diffusion gel growth technique in silica hydro‐gel media. The doping of Mn²⁺ was varied by mixing 0.001M, 0.005M, 0.01M, 0.05M, and 0.1M solutions of MnCl₂ with 1M CaCl₂ solution in equal volumes in the supernatant solutions. The actual amount of Mn²⁺ doping in CLTT crystals was estimated by ICP (Inductively Coupled Plasma) technique. The powder XRD of the samples suggested no significant change in the unit cell dimensions and the presence of any extra phase. The FT‐IR spectra indicated the presence of water molecule, O‐H bond, C‐O bond and carbonyl C=O bond. The EPR spectra confirmed the presence of Mn²⁺ ions in the crystals. The variation of the dielectric constant with temperature confirmed the earlier results of pure calcium tartrate crystals and indicated the ferroelectric nature of the doped crystals. As the amount of doping of Mn²⁺ increased the value of dielectric constant increased. The results are discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase formation in molten system (Na/K)2O‐TiO2‐P2O5. Crystal structures of NASICON and langbeinite‐related phosphates (K/Na)1+xTi2(PO4)3 (x = 0 and 0.357)

Crystallization of high temperature self‐flux of system Na₂O‐K₂O‐TiO₂‐P₂O₅ was investigated at different molar ratios (Na+K)/P = 0.9; 1.0 or 1.2 and Na/K = 1.0 or 2.0 over the temperature range 1000–650°C. The conditions of formation of complex phosphates K_0.10Na_0.90Ti₂(PO₄)₃ (NASICON‐related) and K_0.877Na_0.48Ti^ІІІ_0.357Ti^ІV_1.643(PO₄)₃ (langbeinite‐related) have been established. The new obtained compounds were investigated using FTIR‐spectroscopy, powder and single crystal X‐ray diffraction and optical microscopy methods. The influence of alkaline metal nature on the structure formation of complex phosphates in the high temperature self‐fluxes is discussed.     

Effects of Er3+ doping concentration and calcination on fluorescence properties of La3Ga5.5Nb0.5O14 nanocrystals

The effects of Er³⁺ doping concentration and calcination were examined on the fluorescence properties of La₃Ga_5.5Nb_0.5O₁₄ (Er:LGN) nanoparticles for the first time. High quality Er:LGN nanoparticles were synthesized by sol‐gel method. The room temperature fluorescence spectra showed a green emission, which can be attributed to ²H_11/2‐⁴I_15/2 and ⁴S_3/2‐⁴I_15/2 transition. The relationship between the relative emission intensity and the doping concentration was investigated. The maximum of the Er³⁺ doping concentration in LGN nanopowders is 2.0%. The fluorescent lifetime of 2.0% Er:LGN nanoparticles is 1.45ns. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of lattice parameters and thermal expansion of CuGe2P3 + 0.2 Ge3P4 at elevated temperatures

CuGe₂P₃ is a p‐type semiconductor with zincblende structure. Ge₃P₄ is soluble up to 35 mole% in CuGe₂P₃. Lattice parameters of CuGe₂P₃ + 0.2 Ge₃P₄ have been determined at elevated temperatures from room temperature to 873 K using the x‐ray diffraction profiles (111), (200), (220), (311), (222), (400), (331), (420), (422) and (511) obtained from high temperature diffractometer. It is found that the lattice parameter increases linearly from 0.53856 nm at RT to 0.54025 nm at 873 K. The data on lattice parameter is used and coefficient of lattice thermal expansion of CuGe₂P₃ +0.2 Ge₃P₄ was determined at different temperatures. It is found that the coefficient of thermal expansion of CuGe₂P₃ +0.2 Ge₃P₄ is 5.48 x 10^‐6 K^‐1 and is independent of temperature. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elastic properties of KGd(WO4)2:Ho3+ single crystals studied by Brillouin spectroscopy

The analysis some of the acoustic phonons propagating in pure and Ho³⁺‐doped KGd(WO₄)₂ single crystals in the GHz frequency range by Brillouin scattering method has been presented. For investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101], [101] and [110] have been determined. Moreover, the value of elastic constants C₂₂, C₄₄ and C₆₆ of pure and Ho³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Ho³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% and 8 at%, does not influence their elastic properties. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mild hydrothermal synthesis and structures of mixed‐valence iron phosphates: SrFe3(PO4)3 and the interesting Mg2+‐doped AFe3 (PO4)3 (A = Ba,Pb) in Fe2+ site

Series of mixed valence monophosphates AFe_3‐xMg_x(PO₄)₃ [A = Sr(x = 0), Ba(x = 0.6), Pb(x = 0.6)] were synthesized by mild hydrothermal treatment at 210 °C. Refinements of single crystal X‐ray diffraction datas show all these compounds are isostructural. The attempts to make AFe₃(PO₄)₃ (A = Ba, Pb) hydrothermally in the experiment were unsuccessful. However, the Mg‐doped homologues AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb) were synthesized with the addition of MgCO₃ in the reactants as mineralizer. EDS and single crystal X‐ray data refinement indicated that the Mg²⁺ cations were doped in the Fe²⁺ sites of AFe_2.4Mg_0.6(PO₄)₃ (A = Ba, Pb). The influence of the Mg‐doping on the structure and the reason why the Mg doped in the Fe(II) site instead of A site was discussed from the point of view of the bond valence model.     

Contribution to the study of elastic properties of KGd(WO4)2:Er3+ single crystals by Brillouin spectroscopy

In this paper we present the study of the acoustic phonons propagating in Er³⁺‐doped KGd(WO₄)₂ single crystals by Brillouin spectroscopy. For the investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101] and [110] have been determined. Moreover, the values of the elastic constants: C₂₂, C₄₄ and C₆₆ of Er³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Er³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% does not influence their elastic properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of undoped,Sr2+‐, and Mn2+‐doped ammonium tetrachlorozincate

Crystals of ammonium tetrachlorozincate (AZC) undoped and doped with Sr²⁺ or Mn²⁺ in different concentrations were grown by the slow evaporation method from an aqueous solution. The crystal morphology changed considerably by doping. The dopant concentration in the crystals was measured by the atomic absorption technique. Slight changes in the unit cell parameters of AZC after doping with Sr²⁺‐ or Mn²⁺ have been detected. Optical absorption measurements indicated strong influence of Sr²⁺ and Mn²⁺ doping. The optical energy gap at room temperature decreased continuously with increasing Sr²⁺ and Mn²⁺ concentration but with two different rates. The dc conductivity was also measured as a function of temperature for the undoped and two samples doped with 0.144 Sr²⁺ and 0.191 Mn²⁺ and the results were compared. Positions possibly occupied by Sr²⁺ and Mn²⁺ cations in AZC lattice have been identified. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric constant,loss factor and ac conductivity of Ni2+‐doped K2ZnCl4 crystals in the ferroelectric‐commensurate,incommensurate and normal phases

The dielectric constant (ϵ), dielectric loss (tanδ) and ac conductivity (σ_ac) of virgin and thermally cycled undoped and Ni²⁺‐doped K₂ZnCl₄ (KZC) crystals in the ferroelectric‐commensurate (FC), incommensurate (IC) and normal phases (N) have been studied. Anomalous behaviour at the two‐phase transition points was observed while measuring ϵ along the polar a‐axis for the undoped sample. With increasing Ni²⁺concentration a systematic shift of the phase transition temperature towards lower values and a continuous inhibition of the peak height were detected. ϵ changed linearly with lnf up to f =10⁵ Hz. tanδ along the a‐axis declared the phase transitions by peak changes. After Ni²⁺‐doping this behaviour was preserved at the FC‐IC phase transition point while the IC‐N phase transition was manifested by a change in the slope of the straight line representing the tanδ‐T dependence. The ac conductivity changed lineally with frequency according to a relation of the form σ_ac = σ_o f ^β where 0>β>1.9. σ_ac increased monotonically with increasing temperature and doping concentration in the low‐temperature phases tending to merge in one straight‐line with high activation energy that might be due to superionic dc conduction in the high temperature N‐phase. Doping with Ni²⁺ pinned stripples, decreased the soliton‐soliton interaction, weakened discommensuration effects, shortened the IC‐phase and strongly affected the ‘chaotic' behaviour at the T_C‐IC. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of Yb3+ concentration on Yb:YAl3(BO3)4

The Yb:YAl₃(BO₃) ₄ crystals with different Yb³⁺ doping concentration have been grown by the flux method. The lattice parameters and decomposition of the Yb:YAl₃(BO₃)₄ crystal with different Yb³⁺ doping concentration were measured by X‐ray and DTA method. The transmission and fluorescence spectra of Yb³⁺:YAl₃(BO₃)₄ crystal have been measured. The growth defects of Yb_xY_1‐xAl₃(BO₃)₄ crystals were also detected by using the chemical etching method. The results show that the ytterbium concentration influences these properties of Yb:YAl₃(BO₃)₄. As the Yb³⁺ concentration increased, the crystal lattice parameter was decreased. At high doping level, the absorption peak concerned at about 980 nm shift to short wavelength. It is also found that the perfection of Yb:YAl₃(BO₃) ₄ crystal with low Yb³⁺ doping concentration is better than that with high Yb³⁺ concentration. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Powder study of propanthioamide dervative C8H6N2S2

The crystal structure of 2‐cyano‐3‐(2‐thienyl)prop‐2‐enethioamide (C₈H₆N₂S₂), a propanethioamide derivative was solved from high resolution laboratory X‐ray powder diffraction data collected at ambient conditions. Structure determination was performed by means of the global optimization method of simulated annealing at a resolution of 1.5 Å. Rietveld refinement yielded an R_WP value of 4.02% (P2₁/a, a = 15.8174(2) Å, b = 5.6502(1) Å, c = 11.0952(1) Å, β = 116.9923(7)°, V = 883.6(5) ų, Z = 4). The molecules are stacked in parallel layers and are stabilized by hydrogen bonds. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and spectral analysis of Dy3+ and Er3+ doped KPb2Cl5 as a mid‐infrared laser crystal

This paper reports crystal growth and optical characteristics of dysprosium (Dy³⁺) and erbium (Er³⁺) doped mid‐infrared laser crystal ternary‐potassium‐lead‐chloride (KPb₂Cl₅). Two transparent crystals with good optical quality have been grown successfully by using the Bridgman technique,the largest crystal size reaches up to ∅︁10×60mm². Measurements of X‐ray diffraction(XRD) and absorption spectra were carried out. Based on Judd‐Ofelt theory, the intensity parameters Ω_t(t=2,4,6), the experimental and theoretical oscillator strengths have been obtained.The intensity parameters Ω_t(t=2,4,6) of Er³⁺:KPb₂Cl₅ were calculated to be Ω₂=5.10×10^‐20 cm², Ω₄=1.25×10^‐20 cm², Ω₆=0.83×10^‐20 cm², and the values for Dy³⁺:KPb₂Cl₅ were calculated to be Ω₂=6.26×10^‐20 cm², Ω₄=2.45×10^‐20 cm², Ω₆=0.04×10^‐20 cm² respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Zn2+ ions concentration on the optical properties of Zn/Er:LiNbO3 crystals

Congruent Er³⁺(3 mol%):LiNbO₃ crystals codoped with ZnO (X mol %, X=0, 3, 6 and 7) were grown by the Czochralski technique. The Er contents in the crystals were measured by an inductively coupled plasma atomic emission spectrometer (ICP‐AES). Under 800 nm excitation, the upconversion emission spectra reveal an enhancement of the green emission with respect to the red emission when the Zn²⁺ ions are introduced into Er:LiNbO₃ crystal. The effect of Zn²⁺ ions concentration on the intensity ratio of the green to red emission has been investigated. Two cross‐relaxation processes (²H_11/2 + ⁴I_13/2 → ⁴I_11/2 + ⁴F_9/2 and ⁴F_7/2 + ⁴I_11/2 → ⁴F_9/2 + ⁴F_9/2) are involved in populating the ⁴F_9/2 state, which bypass the green‐emitting states. The OH^‐ absorption spectra indicate that the Zn²⁺ codoping leads to a decreased concentration of Er³⁺ cluster sites contributing to the enhancement of the green emission. The studies on UV‐vis absorption spectra show that the heavily codoped with Zn²⁺ results in the reformation of the Er³⁺ cluster sites in Er:LiNbO₃. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth of the CdGa2(1‐x)Cr2xSe4 compounds by chemical transport method

Single crystals of CdGa_2(1‐x)Cr_2xSe₄ compounds for 0 ≤ x ≤ 1 have been grown by using the chemical vapor transport technique in a closed system. The transporting agent was CdCl₂ in a proportion of 0.75 mg/cc of capsule. The starting material was previously synthetized. The structural characterization on the crystals were done by powder x‐ray diffraction studies. The results show three different phases for various Cr concentration ranges: spinel structure for x ≥ 0.7, rombohedral for 0.6 ≥ x ≥ 0.5 and tetragonal for 0.4 ≥ x ≥ 0. That is, the chromium dilution in the CdCr₂Se₄ compound by Ga atoms produces very significant changes in the structural atomic arrangement. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The color of langatate crystals and its relationship with composition and optical properties

Langatate crystals grown by the Czochralski method in 〈0001〉 and 〈01 1〉 directions both without subsequent annealing (from colorless to orange crystals) and with vacuum (colorless and pale‐green crystals) and air (orange crystal) annealing have been investigated by neutron diffraction, X‐ray diffraction and optical spectroscopy. The main types of point defects were compared with absorption bands: oxygen vacancies ‐ V_O^•• (0.35‐0.36 µm), the vacancies in the lanthanum position ‐ V_La‴ (0.29‐0.30 µm); the absorption band at 0.48‐0.49 µm is typical for the colored samples. The relationship between the X color coordinate (red component) and the oxygen contents has been obtained. The green color of the sample annealed in vacuum is due to the presence of Ta⁺³ ions in the La(Ta³⁺,Ga)O₃ phase that has the structural and geometric agreement with langatate structure. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of CuInS2 single crystals from Sb2S3 and Bi2S3 solutions

The phase diagrams of the CuInS₂‐Sb₂S₃ and CuInS₂‐Bi₂S₃ systems were investigated using X‐ray powder diffraction and differential thermal analysis. Based on these results, the compositions for the growth of the CuInS₂ single crystals from CuInS₂‐Sb₂S₃ and CuInS₂‐Bi₂S₃ melts were selected and Bridgman crystal growth process was performed. The investigation of the obtained single crystals using X‐ray powder diffraction and optical absorption spectra indicates that the incorporation of the solvent atoms into the crystal lattice is absent. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of a new potential second harmonic generation material from the amino acid family: L‐Valinium picrate

L‐Valinium picrate (C₅H₁₂NO₂)⁺. (C₆H₂N₃O₇)^–, a non‐linear optical material from the amino acid family which has large second harmonic generation (SHG) efficiency, was grown by slow evaporation method. Characterization of the crystals was made using single crystal X‐ray diffraction. The functional groups and the modes of vibrations were found by using the Fourier transform infrared (FTIR) spectroscopy. The second harmonic generation (SHG) conversion efficiency was investigated using the Kurtz and Perry method. The SHG conversion efficiency is 60 times higher than that of the standard KDP and 8 times higher than that of the standard Urea and the optical transparency was analyzed using UV‐visible‐NIR absorption spectrum. The structural features of the material leading to the large SHG efficiency are discussed. Microhardness and dielectric studies were also carried out. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Recharging processes of Cr ions in Mg2SiO4 and Y3Al5O12 crystals under influence of annealing and γ ‐ irradiation

Recharging processes of chromium ions were investigated for Mg₂SiO₄:Mg, Cr single crystals using annealing in O₂ and in air and γ‐irradiation, as compare to YAG :Ca, Cr single crystals. The formation of tetravalent Cr ions in the Mg₂SiO₄ :Mg, Cr is related not only to the initial Cr content in the melt, oxygen partial pressure and O₂‐ vacancy existing in the crystal, but also to the external field such as γ‐irradiation. The additional absorption after γ‐irradiation shows the decrease in intensity of the absorption of Cr³⁺ and Cr⁴⁺ ions in some part of the spectrum and increase in the other giving evidence on recharging effects between Cr³⁺ and Cr⁴⁺. There arises also color centers observed between 380 nm and 570 nm that may participate in energy transfer of any excitation to Cr⁴⁺ giving rise to Cr⁴⁺ emission. Opposite to forsterite crystal, absorption spectrum of YAG:Ca, Cr crystal after γ‐irradiation reveals only increase in the absorption of the Cr bands. The observed behavior of the absorption spectrum of YAG:Ca, Cr crystal under influence of γ‐irradiation suggests that γ‐irradiation ionizes only Cr ions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)