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Journal ArticleDOI

Zur kristallstruktur von CaAl2O4

01 Jan 1976-Journal of Inorganic and Nuclear Chemistry (Pergamon)-Vol. 38, Iss: 5, pp 983-984
TL;DR: In this article, a stuffed tridymite structure of CaAl 2 O 4 was re-examined by single crystal X-ray data and the orientation of the tetrahedrals in this tridyclic structure was discussed in comparison with other known compounds.
About: This article is published in Journal of Inorganic and Nuclear Chemistry.The article was published on 1976-01-01. It has received 203 citations till now. The article focuses on the topics: Tridymite.
Citations
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Journal ArticleDOI
TL;DR: The Cemdata18 database as mentioned in this paper contains thermodynamic data for common cement hydrates such as C-S-H, AFm and AFt phases, hydrogarnet, hydrotalcite, zeolites, and M-S -H that are valid over temperatures ranging from 0 to at least 100°C.

526 citations


Additional excerpts

  • ...t calculated 236 from XRD data: pdf 00-038-0237 [48]; u calculated from XRD data; pdf 00-039-1380 [49], : [50], w [51], x [52] 237 238 239...

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Journal ArticleDOI
TL;DR: In this paper, some of the factors involved with different defect centers and interactions between them and the emitting Eu2+ ion are discussed based on the results of systematic investigations carried out on the preparation, composition, structure and different luminescence properties.

440 citations

Journal ArticleDOI
TL;DR: In this article, the structure and properties of glasses and melts in the CaO-Al2O3-SiO2 (CAS) system were investigated using Raman spectroscopy and 27Al Nuclear Magnetic Resonance on CAS glasses obtained by classic and rapid quenching methods.

358 citations


Cites background from "Zur kristallstruktur von CaAl2O4"

  • ...50) (Hörkner and Müller-Buschbaum, 1976), Q and Q in C12A7 (CA0....

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Journal ArticleDOI
TL;DR: A new persistent luminescence mechanism presented is based on the photoionization of the electrons from Eu2+ to the conduction band followed by the electron trapping to an oxygen vacancy, which is aggregated with a calcium vacancy and a R3+ ion.
Abstract: Thermoluminescence properties of the Eu2+-, R3+-doped calcium aluminate materials, CaAl2O4:Eu2+,R3+, were studied above room temperature. The trap depths were estimated with the aid of the preheating and initial rise methods. The seemingly simple glow curve of CaAl2O4:Eu2+ peaking at ca. 80 degrees C was found to correspond to several traps. The Nd3+ and Tm3+ ions, which enhance most the intensity of the high-temperature TL peaks, form the most suitable traps for intense and long-lasting persistent luminescence, too. The location of the 4f and 5d ground levels of the R3+ and R2+ ions were deduced in relation to the band structure of CaAl2O4. No clear correlation was found between the trap depths and the R3+ or R2+ level locations. The traps may thus involve more complex mechanisms than the simple charge transfer to (or from) the R3+ ions. A new persistent luminescence mechanism presented is based on the photoionization of the electrons from Eu2+ to the conduction band followed by the electron trapping to an oxygen vacancy, which is aggregated with a calcium vacancy and a R3+ ion. The migration of the electron from one trap to another and also to the aggregated R3+ ion forming R2+ (or R3+-e-) is then occurring. The reverse process of a release of the electron from traps to Eu2+ will produce the persistent luminescence. The ability of the R3+ ions to trap electrons is probably based on the different reduction potentials and size of the R3+ ions. Hole trapping to a calcium vacancy and/or the R3+ ion may also occur. The mechanism presented can also explain why Na+, Sm3+, and Yb3+ suppress the persistent luminescence.

341 citations

Journal ArticleDOI
TL;DR: In this article, a Gaussian-shaped distribution of trap depths in the presence of a continuous distribution of energy levels is estimated for the violet persistent phosphor CaAl2O4:Eu,Nd.
Abstract: Persistent luminescence or afterglow is caused by a gradual release of charge carriers from trapping centers. The energy needed to release these charge carriers is determined by the trap depths. Knowledge of these trap depths is therefore crucial in the understanding of the persistent luminescence mechanism. Unfortunately, the trap depths in persistent phosphors are often difficult to evaluate in an accurate and reliable way. The existing analysis methods are mostly based on single experiments, or they ignore the possibility of a continuous distribution of trap depths. We present a procedure to accurately probe the activation energies, even in the presence of a continuous distribution of energy levels. By performing a series of thermoluminescence experiments with varying excitation duration and at varying excitation temperature, and employing the initial rise analysis method, the depth and shape of such a distribution can be estimated. As an example, we investigated the trap system in the violet persistent phosphor CaAl2O4:Eu,Nd, and show that it consists of a Gaussian-shaped distribution of trap depths. The maximal density of traps lies in the region around 0.9 eV, but the distribution extends to 0.7 eV on the shallow side and 1.2 eV on the deep side. The described procedure can be used to obtain a clear view of the trap system in other persistent phosphors as well. This can lead to a better understanding of the nature of these trapping centers, and the role they play in the persistent luminescent mechanism.

340 citations

References
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Journal ArticleDOI
10 Aug 1957-Nature
TL;DR: The crystal structure of CaAl2O4 was first examined by Heller as discussed by the authors in connexion with work on the cementing properties of aluminous cement, but due to the difficulty of preparing single crystals, a twinned crystal had to be used and the structure was only partially solved.
Abstract: THE crystal structure of calcium monoaluminate (CaAl2O4) was first examined by Heller1 in connexion with work on the cementing properties of aluminous cement. Owing to the difficulty of preparing single crystals, a twinned crystal had to be used and the structure was, in consequence, only partially solved. In the present investigation it was possible to cut single-crystal fragments from large crystals selected from a sample of phosphorus furnace-slag2.

48 citations

Journal ArticleDOI
TL;DR: In this article, the structure of CaGa2O4 was investigated by X-ray goniometer data and single crystals of the material were prepared and investigated by using a variety of tools.
Abstract: Einkristalle von CaGa2O4 wurden dargestellt und die Kristallstruktur mit Diffraktometer-Rontgendaten bestimmt: a = 10,189, b = 7,725, c = 9,032A, Raumgruppe CPna21. Ga3+ ist tetraedrisch von O2− koordiniert. Ca2+ besitzt unregelmasige Sauerstoffpolyeder. CaGa2O4 stellt einen weiteren Vertreter aufgefullter Silikatstrukturen dar. On Alkaline Earth Oxogallate. III. Investigation of the Structure of CaGa2O4 Single crystals of CaGa2O4 were prepared and investigated by X-ray goniometer data: a = 10.89, b = 7,725, c = 9,032 A. Space group CPna21. Ga3+ is tetrahedrally surrounded by oxygen. Ca2+ has an irregular oxygen coordination. CaGa2O4 is a new member of the stuffed silicate structures.

34 citations

Journal ArticleDOI
TL;DR: In this paper, the crystal structure of monoclinic CaGa2O4 was investigated by X-ray goniometer data: a = 7.992, b = 8.830, c = 10.585 A, β = 94.72°, space group C-P21/C.
Abstract: Von der monoklinen Modifikation der Verbindung CaGa2O4 wurden Einkristalle dargestellt und ihre Kristallstruktur mit Diffraktometer-Rontgendaten bestimmt; a = 7,992, b = 8,830, c = 10,585 A, β = 94,72°, Raumgruppe C—P21/C. Ebenso wie die orthorhombische stellt auch die monokline Modifikation einen weiteren Vertreter der aufgefullten Tridymitstrukturen dar. On Alkaline Earth Oxogallates. V. The Crystal Structure of Monoclinic CaGa2O4 Single crystals of monoclinic CaGa2O4 were prepared and investigated by X-ray goniometer data: a = 7.992, b = 8.830, c = 10.585 A, β = 94.72°, space group C—P21/C. The monoclinic modification represents like the orthorhombic a new member of the stuffed tridymite structure.

34 citations

Journal ArticleDOI
TL;DR: In this article, die Uber-struktur von BaGa2O4 wurde rontgenographisch an Einkristallen untersucht, and die gefundenen Abweichungen von der Sub-strategies betreffen die Verknupfung der GaO4-Tetraeder und Verzerrungen der Sauerstoffpolyeder um Ba.

29 citations