scholarly journals THE OPTICAL SPECTRA OF Co2+ IN MgAl2O4 SPINEL

1991 ◽  
Vol 01 (C7) ◽  
pp. C7-279-C7-283 ◽  
Author(s):  
P. J. DEREN ◽  
W. STREK ◽  
B . JEZOWSKA-TRZEBIATOWSKA ◽  
I. TRABJERG
Keyword(s):  
Optical Spectra ◽  
Mgal2o4 Spinel

Optical Spectra, EPR, and Spin–Lattice Relaxation of Yb3+ Ions in Crystals Having Perovskite-Type Structure

1977 ◽  
Vol 81 (1) ◽  
pp. 287-293 ◽  
Author(s):  
A. A. Antipin ◽  
A. V. Vinokurov ◽  
M. P. Davydova ◽  
S. L. Korableva ◽  
A. L. Stolov ◽  
...  
Keyword(s):  
Lattice Relaxation ◽  
Optical Spectra ◽  
Type Structure ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Perovskite Type ◽  
Perovskite Type Structure

scholarly journals Characterization of M dwarfs using optical mid-resolution spectra for exploration of small exoplanets

2020 ◽  
Author(s):  
Yohei Koizumi ◽  
Masayuki Kuzuhara ◽  
Masashi Omiya ◽  
Teruyuki Hirano ◽  
John Wisniewski ◽  
...  
Keyword(s):  
Sample Selection ◽  
Optical Spectra ◽  
Average Error ◽  
Spectral Energy ◽  
M Dwarfs ◽  
Energy Distributions ◽  
Fitting Procedures ◽  
Optical Region ◽  
Selection For

Abstract We present the optical spectra of 338 nearby M dwarfs, and compute their spectral types, effective temperatures (Teff), and radii. Our spectra were obtained using several optical spectrometers with spectral resolutions that range from 1200 to 10000. As many as 97% of the observed M-type dwarfs have a spectral type of M3–M6, with a typical error of 0.4 subtype, among which the spectral types M4–M5 are the most common. We infer the Teff of our sample by fitting our spectra with theoretical spectra from the PHOENIX model. Our inferred Teff is calibrated with the optical spectra of M dwarfs whose Teff have been well determined with the calibrations that are supported by previous interferometric observations. Our fitting procedures utilize the VO absorption band (7320–7570 Å) and the optical region (5000–8000 Å), yielding typical errors of 128 K (VO band) and 85 K (optical region). We also determine the radii of our sample from their spectral energy distributions. We find most of our sample stars have radii of <0.6 R⊙, with the average error being 3%. Our catalog enables efficient sample selection for exoplanet surveys around nearby M-type dwarfs.

scholarly journals Aggregates of polar dyes: beyond the exciton model

2021 ◽  
Vol 23 (14) ◽  
pp. 8282-8291
Author(s):  
Mattia Anzola ◽  
Anna Painelli
Keyword(s):  
Degrees Of Freedom ◽  
Optical Spectra ◽  
Exciton Model

Optical spectra of aggregates of polar dyes are discussed, fully accounting for polarizability of the dyes and for the coupling of electronic and vibrational degrees of freedom.

scholarly journals Thermodynamics of Mg–Al Order-Disorder Reaction in MgAl2O4-Spinel: Constrained by Prolonged Annealing Experiments at 773–1123 K

Molecules ◽  
2021 ◽  
Vol 26 (4) ◽  
pp. 872
Author(s):  
Yunlu Ma ◽  
Xinjian Bao ◽  
Xi Liu
Keyword(s):  
Spinel Structure ◽  
Structural Model ◽  
Molar Fraction ◽  
Thermodynamic Models ◽  
Mgal2o4 Spinel ◽  
Cation Order ◽  
Prolonged Annealing ◽  
Wide Range ◽  
History Of ◽  
Annealing Experiments

MgAl2O4-spinel has wide industrial and geological applications due to its special structural and physical–chemical features. It is presumably the most important endmember of complex natural spinel solid solutions, and therefore provides a structural model for a large group of minerals with the spinel structure. There exists a well known but still inadequately understood phenomenon in the structure of MgAl2O4-spinel, the Mg–Al cations readily exchanging their positions in response to variations of temperature, pressure, and composition. A large number of experiments were performed to investigate the Mg–Al cation order-disorder process usually quantified by the inversion parameter x (representing either the molar fraction of Al on the tetrahedral T-sites or the molar fraction of Mg on the octahedral M-sites in the spinel structure), and some thermodynamic models were thereby constructed to describe the x-T relation. However, experimental data at some key T were absent, so that the different performance of these thermodynamic models could not be carefully evaluated. This limited the interpolation and extrapolation of the thermodynamic models. By performing some prolonged annealing experiments with some almost pure natural MgAl2O4-spinel plates and quantifying the x values with single-crystal X-ray diffraction technique, we obtained some critical equilibrium x values at T down to 773 K. These new x-T data, along with those relatively reliable x values at relatively high T from early studies, clearly indicate that the CS94 Model (a model constructed by Carpenter and Salje in 1994) better describes the Mg–Al cation order-disorder reaction in MgAl2O4-spinel for a wide range of T. On the basis of the CS94 Model, a geothermometer was established, and its form is T-closure = 21362 × x3 − 12143 × x2 + 6401 × x − 10 (T-closure standing for the closure temperature of the Mg–Al cation exchange reaction). This geothermometer can be used to constrain the thermal history of the geological bodies containing MgAl2O4-spinel.

Optical spectra of lithium vapour zones produced by thermal evaporation in hydrogenating atmosphere

1999 ◽  
Vol 11 (6) ◽  
pp. 1621-1629 ◽  
Author(s):  
Shosuke Mochizuki ◽  
Mie Sasaki ◽  
Raphael Ruppin
Keyword(s):  
Thermal Evaporation ◽  
Optical Spectra

Discovery of five new Galactic symbiotic stars in the VPHAS+ survey

2021 ◽  
Vol 502 (2) ◽  
pp. 2513-2517
Author(s):  
Stavros Akras ◽  
Denise R Gonçalves ◽  
Alvaro Alvarez-Candal ◽  
Claudio B Pereira
Keyword(s):  
Spectroscopic Data ◽  
Selection Criterion ◽  
Optical Spectra ◽  
Emission Lines ◽  
High Rate ◽  
Symbiotic Stars ◽  
Selection Of

ABSTRACT We report the validation of a recently proposed infrared (IR) selection criterion for symbiotic stars (SySts). Spectroscopic data were obtained for seven candidates, selected from the SySt candidates of Akras et al. by employing the new supplementary IR selection criterion for SySts in the VST/OmegaCAM Photometric H-Alpha Survey. Five of them turned out to be genuine SySts after the detection of H α, He ii, and [O iii] emission lines as well as TiO molecular bands. The characteristic O vi Raman-scattered line is also detected in one of these SySts. According to their IR colours and optical spectra, all five newly discovered SySts are classified as S-type. The high rate of true SySts detections of this work demonstrates that the combination of the H α emission and the new IR criterion improves the selection of target lists for follow-up observations by minimizing the number of contaminants and optimizing the observing time.

Lattices selective occupation, optical spectra regulation, and photoluminescence properties of Eu2+ activated Ca9La(PO4)7 phosphor

2021 ◽  
pp. 118197
Author(s):  
Mingxue Xu ◽  
Chenli Fan ◽  
Chen Yang ◽  
Kaixin Song ◽  
Fayaz Hussain ◽  
...  
Keyword(s):  
Optical Spectra ◽  
Photoluminescence Properties
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