Luminescence in some tantalate host lattices

The luminescence of the following systems are reported: ScTa_1−xNb_xO₄, Li₃Ta_1−xNb_xO₄, CaTa_2−2xNb_2xO₆ and Mg₄Ta_2−2xNb_2xO₉. The dependence of the luminescence properties on x becomes more pronounced if the distance between the pentavalent ions becomes shorter. In these systems the NbO₆ group gives an efficient blue emission at 300°K. The compound Mg₄Ta₂O₉ gives an efficient ultraviolet emission at 300°K. At 77°K both Mg₄Nb₂O₉ and Mg₄Ta₂O₉ show in addition a weaker emission peaking at wavelengths longer than the wavelength of the room temperature emission. This low-temperature emission can be excited by radiation with wavelengths longer than that of the absorption edge. The Mn²⁺ ion in Mg₄Ta₂O₉Mn acts as an efficient activator with a deep-red emission.     

Amidinoethylation—a new reaction—IV : The amidinoethylation of alcohols: a facile synthesis of 3-alkoxy-N,N'-substituted-propanamidines

The amidinoethylation of alcohols takes place by the addition of sodium alkoxides 2 (R¹ = Me, Et) to the CC double bond of a variety of N,N'-substituted-propenamidines 1 (Method A). This illustrates the activation of the CC double bond by the conjugated amidine function and provides a new class of Michael acceptors for alcohols. However, this activation is poorer than with other nucleophiles or Michael acceptors. The amidinoethylation makes available 3-alkoxy-N,N'-substituted-amidines not easily accessible by other classical methods. However, it is demonstrated that the general N,N'-substituted-amidine synthesis via the nitrilium salts can also apply to nitrile compounds having an alkoxygroup present on the molecule (method B). Since the cyanoethylation of alcohols (4) is a very fast and facile reaction the method B is the preferred strategy for the synthesis of 3-alkoxy-N,N'-substituted-propanamidines 3.     

The Michael Addition of Enamines to Propenamidines. A Convenient Synthesis of 2β-Amidinoethylcyclo-Alkanones by Amidinoethylation Reaction

A variety of propenamidines 3 have been reacted with enamines of cyclopentanone and cyclohexanone giving after hydrolysis of the Stork enamine 6, 2-β-amidinoethylcyclopentanones 8 and -hexanones 7. This reaction illustrates the electrophilic character of the C=C double bond due to the conjugated amidine function, thus providing with propenamidines 3 a new class of Michael acceptors for enamines.     

Luminescence of Eu2+-activated Cs(Ca,Mg)F3 and Rb(Ca,Mg)F3

In the system CsCa_0.95?xMg_xEu_0.05F₃ a new phase has been found with x ≈ 0.7, which gives efficient blue luminescence. For RbCa_0.95?xMg_xEu_0.05F₃ efficient green luminescence is obtained at x ≈ 0.5.     

Two photon luminescence with ultraviolet excitation of trivalent praseodymium

In the fluorides YF₃ and α-NaYF₄, the trivalent praseodymium ion shows a two photon luminescence in which one ultraviolet photon (?210 nm) is converted into two visible photons.     

Dosage de traces de silicium dans les métaux à l'aide des ions silicomolybdiques non réduits

Sans résumé     

Line emission of SrAl12O19: Eu2+

The luminescence of SrAl₁₂O₁₉: Eu²⁺ consists of a 5d—4f broad-band emission and of 4f—4f lines, their relative intensities being strongly dependent on temperature. At 77°K mainly line emission is observed.     

Method for Estimation of Hydroxyl Concentration Behind the Reflected Shock Wave Front Using Broadband Radiation Source and Detector

Journal of Applied Spectroscopy - An absorption spectroscopy method is proposed for estimating hydroxyl concentration behind the reflected shock wave front without lasers and high-resolution...     

Amidinoethylation—a new reaction—III : The amidinoethylation of amino-compounds: a facile synthesis of 3-aminosubstituted-N,N'-substituted-propanamidines

The amidinoethylation of amino compounds takes place by the addition of amines to the CC double bond of a variety of N,N'-substituted-propenamidines 1. The most nucleophilic amines such as piperidine, morpholine and pyrrolidine add under very smooth conditions. 1 hr reflux in acetonitrile as solvent and without catalyst. Aliphatic amines such as cyclohexylamine and diisopropylamine require more drastic conditions, higher heating temperature and longer reaction time. Aromatic amines add in the presence of acetic acid, however under these conditions transamidination side reactions are observed. These results illustrate the activation of the CC double bond of propenamidines by the conjugated amidine function thus providing a new class of Michael acceptors for amino compounds. Furthermore the amidinoethylation makes available 3-ammosubstituted-N,N'-substituted-propanamidines 3 not easily accessible by other classical synthetic methods.     

Détermination spectrophotométrique de l'aluminium et du fer dans les siliciums industriels

Résumé Le dosage colorimétrique de l'aluminium par le ferron a été précisé et les modalités de son application à l'analyse des siliciums et ferrosiliciums décrites. La précision est de l'ordre de celle de la gravimétrie de l'oxinate, et le procédé, qui permet en même temps la détermination du fer, est beaucoup plus rapide.

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Summary The colorimetric determination of aluminium by ferron has been made exact and the methods of applying it to the analysis of silicon and ferrosilicons are described. The accuracy is of the order of the gravimetric oxinate procedure and the method which permits the simultaneous determination of iron, is much faster.

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Zusammenfassung Die kolorimetrische Bestimmung des Aluminiums mittels Ferron wurde ausgearbeitet und ihre Anwendung auf die Analyse von Silicium und Ferrosilicium beschrieben. Die Genauigkeit des Verfahrens entspricht der Gravimetrie des Oxinats. Es ist aber rascher und gestattet gleichzeitig die Bestimmung des Eisens.

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Avec la collaboration deP. van de Leur