New garnet crystal potentially suited for mini-laser devices of 1.5-μm spectral range

In Er:doped crystals, the 1.5-μm (⁴I_13/2–⁴I_15/2) transition is of negligibly small intensity. To intensify this transition, the (Gd,Y)₃(Ga,Sc)₅O₁₂ host crystal has been chosen as a basic medium. The single crystal garnet films with thickness up to 18-μm were grown using the method of liquid-phase epitaxy on Gd₃Ga₅O₁₂ substrates. The 20-at.% maximal concentration of Er³⁺-ions was achieved without luminescence quenching. The up-conversion processes were neutralized by the addition of an Fe-ions sensitizer. At the same level of absorbed pumping power, the luminescence intensity at the 1.5-μm band for the Er:Fe:doped crystal was approximately one to two orders of magnitude higher than that for traditional content. Heavily doped crystals demonstrated broadening of the luminescence band up to 300 nm.     

Unusual Glassy Smectic-G Liquid Crystal: Heat Capacity of N-p-n-Pentyloxybenzylidene-p'-n-butylaniline between 11 and 393 K

Abstract

The heat capacities of the title compound (C₃H₁₁,O—C₆H₄,- CH=N—C₆H₄,—C₄H₉, abbreviation 5O ? 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → S_G, S_G → N and N → isotropic liquid were T _c = 299.69 K/ΔH = 22.68 kJ mol^?1/ΔS = 75.70 JK^?1 mol^?1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The S_A phase hitherto reported in between S_G and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy S_G state at 0 K was by (10.1±0.1) kJ mol^?1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK^?1 mol^?1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the S_G state of 6O?4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy S_G states. Two possible origins responsible for the double glass transitions have been discussed.     

Relationship between defects and optical properties in Er-doped GaN

The density of the vacancy-type defect in Er doped GaN was measured by positron annihilation spectrometry (PAS) and the correlation between the intensity of the Er-related luminescence was studied. A luminescence peak at 558 nm originating from ⁴S_3/2 to ⁴I_15/2 transition of Er³⁺ was observed in Er-doped GaN. The intensity of the luminescence increased with increasing Er concentration and showed the maximum with the Er concentration of around 4.0 at%. The PAS measurements showed that the vacancy-type defect density increased with increasing Er concentration up to 4 at%, and around 4 at% of Er, the formation of defect complex such as V_Ga–V_N was suggested. The contribution of the defect to the radiative recombination of intra-4f transition of Er is discussed.     

Phase transitions from density and order parameter from polarisabilities in symmetric dimeric liquid crystals

As a part of our systematic studies on liquid crystal dimers, we present in this article the nature of phase transitions across isotropic–nematic and nematic–smectic-A exhibited by DLCs, α,ω-bis-(4-n-alkylaniline benzylidene-4?-oxy) alkanes. Further, the orientational order parameter in the nematic phase of these DLCs are estimated from the molecular polarisabilities calculated using the experimental refractive indices and density results. The molecular polarisabilities α_e and α_o are obtained for the compounds using the above results for both Vuks and Neugebauer local field models applicable to nematic liquid crystal. α_e and α_o calculated in this way are used to obtain Δα. The polarisability anisotropy in the perfect order (absolute K) is calculated semi-empirically using the δ-function model developed by Lippincott et al. and molecular vibration method. The values of polarisability anisotropy for both local electric field models differ significantly. No criterion is known to decide which value is correct. To avoid the determination of uncertain α and Δα values considering different local field models, a simple procedure developed by Kuczynski et al. was used for evaluation of S, based solely on birefringence δn = (n_e-n_o) and this value of S is compared with those obtained from field models.     

Growth of bulk zinc chalcogenide single crystals from the vapour phase and their use for laser screens of projection colour television

Results on ZnSe, ZnSe_xS_1−x and ZnS crystal growing from the vapour phase up to 7.5 cm³ in volume are described. Crystals were grown on sapphire, ZnS, ZnSe_xS_1−x and quartz glass substrates without a contact of the growing crystal with a growth ampoule and using the molten tin as a heating medium. Large high-purity crystals with a density of etch pits of 10³ cm⁻² were obtained They exhibited an effective exciton luminescence and rather high radiation efficiency (30 ± 10% for ZnSe at T = 77 K). This made it possible to use these crystals for fabricating laser screens for a cathode ray tube. The main laser parameters obtained on a ZnSe screen at T = 80 and 300 K using a 75 keV electron beam excitation are presented. The light power output reached 0.8 W at T = 80 K; this allowed to obtain a 10 cd · m⁻² TV image of 1.5 × 2 m² in area.     

Structure and optical properties of chalcohalide glasses doped with Pr and Yb ions

Glasses of systems 100-y((GeS₂)₈₀(Sb₂S₃)_20−x(PbI₂)_x)yPr₂S₃, x = 0; 2; 5, 8; y = 0; 0.01; 0.1; 0.5 and 99.9-z((GeS₂)₈₀(Sb₂S₃)₁₈(PbI₂)₂)0.1Pr₂S₃zYb₂S₃, z = 0.05; 0.1; 0.15) were synthesized in high purity. Optically well transparent glasses were obtained for x  5 mol.% PbI₂, for y  0.1 mol.% Pr₂S₃ and for z  0.15 mol.% Yb₂S₃. The glasses were stable and homogeneous, as confirmed by X-ray diffraction and electron microscopy, with high optical transmittivity from visible (red) region up to infrared region (900 cm⁻¹). The density of the glasses was 3.26–3.33 gcm⁻³ for PbI₂ containing glasses. The glass transition temperature, T_g, was 320–336 °C. The optical absorption bands in rare-earth doped glasses corresponded to ³H₄–³F₄, ³H₄–³F₃, ³H₄–(³F₂ + ³H₆) f–f electron transitions of Pr³⁺ ions and to ²F_7/2–²F_5/2 f–f electron transitions of Yb³⁺ ions. Strong luminescence band with maximum near 1340 nm (electron transition ¹G₄–³H₅) was found in Pr₂S₃ doped glasses. The intensity of this band was rising with doping by Yb³⁺ ions. The possible mechanism of the luminescence enhancement is suggested.     

Liquid Crystalline and Luminescent Behavior of Lanthanide Complexes Composed of Terbium or Europium and Dendritic Amphiphile

Luminescent lanthanide (Tb³⁺, Eu³⁺) complexes were prepared by reaction of Tb³⁺ or Eu³⁺ with dendritic amphiphile (3,4,5-tris(dodecyloxy)benzoate), then their liquid crystalline and luminescent behavior were studied. The complexes exhibited thermotropic liquid crystalline mesophases with columnar hexagonal structure. The complexes emitted the characteristic luminescence of the core metals. Additionally, in the Eu³⁺ complex, the ratio of the intensity of 614 nm to the intensity of 585 nm (I₆₁₄/I₅₈₅) remarkably decreased around the transition temperature from crystal to mesophase, suggesting that the coordination environment of Eu³⁺ gets more symmetrical due to the phase transition.     

Crystal and molecular structure of 3,6-dihydro-4,5-dimethyl-2-[2-(methoxymethyl)pyrrolydinesulfonyl]-2-phenyl-2H-thiapyran-1-oxide,C19H27NO4S2

The crystal structure of a dihydrothiapyranS-oxide was determined from single-crystal diffractometer data, C₁₉H₂₇NO₄S₂, MoK radiation: orthorhombic, space groupP2₁2₁2₁, usinga=8.9604(10),b=13.5928(15),c=16.5621(19) Å,z=4. The molecule has theE-geometry, and the absolute configuration isR at C₁ andS at S₁.     

Synthesis and Liquid Crystal Behaviour of Further 4,4″-Disubstituted 2'-Fluoro-1,1':4',1”-Terphenyls

Further to earlier work on the liquid crystal properties of fluoro-1,1':4',1”-terphenyls¹ we have now extended this series to include terminally fluoro-and cyano-substituted 2'-fluoro-1,1':4',1″-terphenyls, chiral 2'-fluoro-1,1':4',1″-terphenyls, and esters derived from 2'-fluoro-1,1':4',1”-terphenyls and incorporating the alkylcyclobutyl group. The preparations and transition temperatures for these series of compounds are presented and their transition temperatures and mesophase types are discussed. An interesting result from this work was the appearance of an S^* _C phase for one chiral homologue and of S _c phases for the esters incorporating the alkylcyclobutyl group. The S _c formation is attributed to the presence of the fluoro-substituent.

Keywords: terphenyls, fluoroterphenyls, smectic C phases, cyclobutyl esters     

1540 nm fiber laser excited upconversion luminescence in erbium-doped lead-fluoride nanocrystals

Upconversion luminescence in erbium-doped PbGeO₃-PbF₂-CdF₂-based vitroceramic under 1540 nm infrared excitation is investigated. Luminescence signals around 410, 525, 550, 660 and 850 nm were generated and attributed to the ²H_9/2, ²H_11/2, ⁴S_3/2 and ⁴F_9/2 transitions to the ⁴I_15/2 ground-state, and ⁴S_3/2-⁴I_13/2, respectively. The erbium ions excited-state emitting levels were populated through a combination of stepwise ground-state absorption, phonon-assisted excited-state absorption and cross-relaxation processes. The results also disclosed that all emission signals obtained with vitroceramic samples presented intensities three times higher when compared to the precursor glass samples. In addition, the red emission signal at 660 nm for 1540 nm pumping exhibited an expressively high intensity when compared to the green signal.     

The crystal structure of the molecular complex of camphoramic acid with mandelic acid: A partial separation of a racemic mixture of mandelic acid by (1R,3S)-camphoramic acid

From an ethanol/water solution containing (1R,3S)-camphoramic acid and a racemic mixture of mandelic acid, the title complex crystallizes in the space group P2₁2₁2₁ with a = 8.015(2), b = 11.041(2), c = 21.781(4) Å. Both molecular complexes, the (1R,3S)-camphoramic acid (S)-mandelic acid complex and the (1R,3S)-camphoramic acid (R)-mandelic acid complex, randomly distribute in a disordered crystal structure with an approximate molar ratio of 3:1, thus a 3:1 separation of the mandelic acid enantiomers was achieved. Molecules of (S)-mandelic and (R)-mandelic acid form very similar intermolecular interactions with adjacent camphoramic acid and water molecules in the structure. This results in the formation of a cocrystal containing two diastereomers. The crystal structure consists of camphoramic acid layers and mandelic acid layers. An extensive H-bonding network occurs within and between the layers.     

Calorimetric Study of Crystalline and Liquid-Crystalline Polymorphism in the Homologues of Terephthal-bis-n-alkylaniline

The phase sequences of the homologues with n (the number of carbon atoms in the terminal alkyl chains) from 2 to 8 are obtained. At low temperatures, i) several crystalline modifications are found in each of the members with n = 4, 5, and 6 and ii) the monotropic transitions between crystal and smectic phase are observed in almost all the members. At intermediate temperature, iii) between the smectic H and C phases, the smectic F phase is found in the homologues with n ≥ = 5 by morphological observation or by a rheological method. The constancy of the temperature of the S_H(or S_F) – S_c transition with respect to “and broadening of the temperature range of S_H with increasing n in the expense of nematic phase are worthy of note. The even-odd effect of the end chain length n is observed very distinctively on the crystal melting and clearing point. Proton NMR measurement reveals a large mobility in the terminal alkyl chains in the crystal of the member with n = 6.     

Crystal and molecular structure of 1-phenyl-6-(phenylthio)-3H-2,1,3-benzoxathiazolium-3-olate

The crystal structure of 1-phenyl-6-(phenylthio)-3H-2,1,3-benzoxathiazolium-3-olate, C₁₈H₁₃NO₂S₂, has been determined by X-ray single crystal diffraction. The crystals are monoclinic, space groupP2₁,Z = 2, witha = 8.757(2),b = 8.428(2),c = 11.332(3) Å, and = 101.34(2) °. All intensity measurements were made at room temperature on an Enraf-Nonius CAD-4 automatic diffractometer using monochromatized, MoK radiation. The final agreement factorR was 0.029 for 1465 contributing reflections. The nitrophenyl moiety is essentially planar, and the two phenylthio rings are canted at 74 ° and 87 ° to it. There is a possible nonbonded attraction between the nitro group and theortho-sulfur.     

Synthesis and Crystal Structure of Chiral ( S , R Fc )- N -1-(2-Diphenylphosphino)ferrocenylethyl-2-hydroxyl-3,5-di- tert -butylbenzalimine

Abstract The title compound, (S, R _Fc )-N-1-(2-diphenylphosphino)ferrocenylethyl-2-hydroxyl-3,5-di-tert-butylbenzalimine was synthesized by the treatment of (S, R _Fc )-1-(2-diphenylphosphino)ferrocenylamine with 3,5-di-tert-butyl salicylaldehyde and its crystal structure determined. Single crystal X-ray diffraction analysis reveals that the molecular structure of the title compound is enantiomerically pure. The crystal belongs to noncentrosymmetric, space group P2₁2₁2₁, with unit cell parameters a = 9.3792(8) ?, b = 12.6524(10) ?, c = 28.858(2) ?, V = 3424.6(5) ?³, D _x = 1.221 g cm⁻³, Z = 4, T = 293(2) K, F(000) = 1336, R ₁ = 0.0435 and wR ₂ = 0.1039. Index Abstract The title compound, (S, R _Fc )-N-1-(2-diphenylphosphino)ferrocenylethyl-2-hydroxyl-3,5-di-tert-butylbenzalimine was synthesized by the treatment of (S, R _Fc )-1-(2-diphenylphosphino)ferrocenylamine with 3,5-di-tert-butyl salicylaldehyde and its crystal structure determined. Single crystal X-ray diffraction analysis reveals that the molecular structure of the title compound is enantiomerically pure.      

The Internal Field Parameters for Liquid Crystals

This paper presents calculations of the internal field constants γ_e for four homologous liquid crystal materials in their nematic and crystalline phases. We find that for the nematic phase, the γ_e ～ S ₂ curve is nearly a straight line for each compound. When one extrapolates the straight line to S ₂ = 1, the corresponding γ_e value is nearly equal to γ∥, the crystalline internal field constant. The birefringence data used are those reported by Somashekar et al.⁴ The four compounds studied are:

(1) p(p'-ethoxyphenylazo)phenyl valerate;

(2) p(p'-ethoxyphenylazo)phenyl hexanote;

(3) p(p'-ethoxyphenylazo)phenyl heptanoate;

(4) p(p'-ethoxyphenylazo)phenyl undecylenate.     

Crystal structures of a pair of diastereomeric 3-(N,N-dimethylammonium)-1,1-diphenyl-1-butanol hydrogen tartrates

The crystal structures of a pair of diastereomeric salts of (2R, 3R)- (+)-tartaric acid and (–)-and (+)-3-N,N-dimethylamino-1,1-diphenyl-1-butanol have been determined. Crystal data: 1: (R)-(–)-C₁₈H₂₄NO⁺, , C2, a = 38.198(7), b = 5.841(2), c = 9.993(2)Å, = 102.63(1)°, V = 2175.6(1) ų, Z = 4, D _calc = 1.281 g cm^–3. 2: (S)-(+)-C₁₈H₂₄NO⁺, P2₁2₁2₁, a = 6.037(2), b = 8.5947(8), c = 39.74(1)Å, V = 2062.0(9) ų, Z = 4, D _calc = 1.351 g cm^–3. The conformations of the 3-(N,N-dimethylammonium)-1,1-diphenyl-1-butanol cations in the two salts are almost mirror images of each other, but the cation in 2 has an intramolecular hydrogen bond. The hydrogen tartrate ions adopt an extended conformation. The hydrogen bonding networks in the two salts are very different. The absolute configuration of (–)-3-(N,N-dimethylamino)-1,1-diphenyl-1-butanol (1) was established as R.     

Optical and laser properties of Nd:LuVO4 crystal

Polarized absorption spectra of Nd:LuVO₄ crystal were measured at room temperature. The optical parameters of π polarization and σ polarization were calculated by Judd‐Ofelt theory. Meanwhile, the phenomenological intensity parameters: Ω₂, Ω₄, and Ω₆ were obtained, then the parameters were used to calculate the luminescence parameters of Nd:LuVO₄ crystal, including oscillator strengths, fluorescence branching ratio, radiative lifetime and integrated emission cross‐sections. Experiments of a‐cut and c‐cut Nd:LuVO₄ lasers were also performed, and opt‐opt conversion efficiency and slope efficiency were 40.3%, 50.5% for a‐cut and 23.6%, 30.9% for c‐cut, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and absolute configuration of enhydrin bromohydrin

X-ray study of enhydrin bromohydrin, C₂₃H₂₉BrO₁₀, reveals that the crystal has space groupP2₁2₁2₁ with cell parametersa =10.08,b = 26.97, andc = 8.94 Å. There are four molecules in the unit cell. The structure was solved by direct methods, with three-dimensional CuK diffractometer data to = 75 °, and refined by block-diagonal least squares to anR index of 11.4% for 2254 reflections. The molecule is a germacronolide sesquiterpene having acis sterochemistry at the C(1), C(10) double bond and atrans configuration at the epoxide ring, C(4)-O-C(5). The absolute configuration established on the basis of the anomalous scattering of CuK. radiation by the bromine atom shows that the asymmetric atoms have the 4R, 5R, 6S, 7S, 8S, 9S, 20S, and 22S configurations.     

Cleavage Mechanoluminescence in Crystals

When a crystal is cleaved, initially the mechanoluminescence (ML) intensity increases linearly with time, attains an optimum-value I_m at a particular value of timet_m, and then decays exponentially with time. Cleavage ML provides a new tool to determine the velocity, v of cracks in crystals, and it may be given by v = H/t_m, where H is the thickness of the crystal. Both, the peak ML intensity I_m and total ML intensity I_T increase linearly with the area of newly created surfaces A as well as with the surface charge density γ. The ML intensity decreases with temperature primarily due to the decrease in the surface charge density. Beyond a particular temperature, the surface charge density may decrease to such a value where the breakdown of gases and solids may not be possible and thereby the ML may not appear. Depending on the prevailing conditions either the ML emission resembling gas discharge or other types of the luminescence of solids, or that having these two characters may be obtained. There exists a good correlation between the theoretical and experimental results obtained for cleavage ML in crystals.     

Stereospecific Ligands and Their Complexes. III. Oxalato and Malonato-(ethylenediamine- N , N ′-di- S , S -2-propionato)-Chromate(III) Complexes. Crystal Structure of the Δ-(–)589- s - cis -K[Cr( S , S -eddp)(ox)]?·?0.5H2O

Abstract  The s-cis-[Cr(S,S-eddp)L]⁻ complexes (S,S-eddp = S,S-ethylenediamine-N,N′-di-2-propionate ion; L = oxalate or malonate ions) were prepared. The complexes were purified by ion-exchange chromatography. The geometry of the complexes has been supposed on the basis of the electronic absorption spectra, and the absolute configurations of the isolated s-cis-[Cr(S,S-eddp)L]⁻ complexes have been predicted on the basis of their circular dichroism (CD) spectra and confirmed by X-ray analysis of the crystal structure of the Δ-(–)₅₈₉-s-cis-K[Cr(S,S-eddp)(ox)] 0.5H₂O complex. Index Abstract  The title compound, s-cis-potassium-(ethylenediamine-N,N’-di-S,S-2-propionato) (oxalato)chromate(III) semihydrate was synthesized by passing the corresponding sodium salt through cation exchange-resin Merck I in potassium form and its crystal structure determined. Single crystal X-ray diffraction analysis reveals s-cis geometry of the complex cation. For Part II see Glodjović VV, Trifunović SR (2008) J Serb Chem Soc 73:541.