Search results for "Exciton"

<title>Electronic excitations and defects in fluoroperovskite LiBaF<formula><inf><roman>3</roman></inf></formu…

2003

A survey of the present situation with respect to knowledge of lattice defects, electronic excitations, such as excitons and localized excitons, as well as energy storage and transfer phenomena in LiBaF3 crystals is given. Both phenomenological models and experimental interpretations of optical absorption bands, tentatively associated with F-type (electron) centers created by X-ray or electron irradiation, is reviewed. Interpretation of three radiative processes (super-fast core-valence transitions, slow trapped exciton luminescence and luminescence of structure defects) observed in undoped LiBaF3 crystals is analyzed with respect to practical application. Attention is paid to the behavior …

<title>High-excitation-density luminescence as probe of mixed silver halides</title>

1992

Two kinds of intrinsic luminescence in mixed AgBr1-xClx (1 io. Dependence of the parameters of this process on crystal composition has been investigated in terms of spatially well correlated Frenkel defect recombinations. The main effect found was the linear increase of the Agio migration energy with the crystal composition x. The second kind of luminescence arising due to exciton molecules has been shown to be sensitive to the solid solution composition and the quality of a crystal. It is shown that this luminescence correlates with the optical losses of the fibers studied.

Photostimulated emission of KBr—In previously exposed to UV- or X-radiation

1995

Abstract We have performed a photostimulated luminescence (PSL) study of a KBr—In crystal previously irradiated in the exciton fundamental absorption band. It is shown that the PSL arises from three types of close defect pair. It is also shown that one of these three kinds of defect pairs is {F, In2+}, whereas the electron centre of the two other pairs has a more complex nature.

Transient Optical Absorption and Luminescence in Calcium Tungstate Crystal

2001

Single-Exciton Amplified Spontaneous Emission in CsPbX3 (X = Br, I) Perovskite Nanocrystals

2019

Exciton interactions in self-organised bacteriochlorophyll a - aggregates

2002

Exciton interactions of self-organised bacteriochlorophyll a - aggregates in non-polar solution linked via water and dioxane have been studied. Absorption and CD spectra of the aggregates show large red shifts typical of J-aggregates. Femtosecond excitation of the Qy band of the aggregates is followed by wavelength dependent non-exponential picosecond relaxation and anisotropy decay takes place in subpicosecond time scale. To explain these observations exciton theory and semi-empirical MO/CI calculations, that constitute the basis of the CIEM-approach developed by Linnanto et al. (J. Phys. Chem. B, 1999, 103B, 8739) was used. Structural models of aggregates were created by using the molecul…

Exciton Interactions and Femtosecond Relaxation in Chlorophyll a−Water and Chlorophyll a−Dioxane Aggregates

1998

Chlorophyll a (Chl a) in hydrocarbon solution with a small amount of dioxane or water shows red-shifted absorption bands at 686 nm and at 700 nm (dioxane) and at 745 nm (water), indicative of self-organized aggregate structures in solution. To study the relationship between the structure and spectral properties of the aggregates, several one-dimensional model structures of Chl a−dioxane and Chl a−water aggregates were computed by the molecular mechanics method. Three overall structures ranging from stick to a ring shape were energetically favored for the dioxane system. All these structures contain structural heterogeneity that consists of repeating dimers that further form tetramer substru…

Luminescence of intrinsic defects in YAG polycrystalline powder

1997

In the present work we have investigated luminescence properties of the fine, well-crystallized undoped YAG polycrystalline powders and thermochemically treated YAG polycrystalline powders. Presented work give evidence of significant role of 'antisite' defects (AD), i.e., where some portion of one type of cations (Y 3+ ) occupy another cations (Al 3+ Oh ) sites and vice versa in YAG structure, on the creation and structure of luminescence centers in complex multi-component oxides.

<title>Origin of visible photoluminescence in NiO and Ni<formula><inf><roman>c</roman></inf></formula>Mg&lt…

2003

A study of the visible photoluminescence in single-crystal NiO and NicMg1-cO (c = 0.99, 0.98 and 0.95) solid solutions is presented for the first time. Two wide luminescence bands, peaked at approximately 12000 cm-1 and approximately 18500 cm-1, were observed. The dependence of their intensity and position on the excitation energy, temperature, and composition were investigated. We attribute the origin of two photoluminescence bands to the impurity- or defect perturbed Ni2+ excitons.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

<title>Primary radiation defect formation in silver halides</title>

1998

Under irradiation the formation of primary intrinsic defects in silver halide solid solutions AgBr1-xClx take place via strong exciton-phonon interaction. Efficiency of these defects formation depend on solid solution composition and within 0 <EQ x <EQ 0.15 dependence on temperature was observed too. Estimation shows efficiency of defects creation is approximately 0.01 for AgCl and noticeably higher for AgBr.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.