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2D metal halide perovskites: a new fascinating playground for exciton fine structure investigations

Baranowski Michał, Dyksik Mateusz, Płochocka Paulina

Scientiae Radices

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2022

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Vol. 1, Iss. 1

3--25

EN

Two-dimensional (2D) metal halide perovskites are natural quantum wells which consist of low bandgap metal-halide slabs, surrounded by organic spacers barriers. The quantum and dielectric confinements provided by the organic part lead to the extreme exciton binding energy which results in a huge enhancement of exciton fine structure in this material system. This makes 2D perovskites a fascinating playground for fundamental excitonic physics studies. In this review, we summarize the current understanding and quantification of the exciton fine structure in 2D perovskites. We discuss what is the role of exciton fine structure in the optical response of 2D perovskites and how it challenges our understanding of this fundamental excitation. Finally, we highlight some controversy related to particularly large bright-dark exciton states splitting and high efficiency of light emission from these materials. This can result from the unique synergy of excitonic and mechanical properties of 2D perovskites crystals.

2

Comparison of the Properties of False Twist Textured Super Bright, Semi-dull, Grey and Black Dope Dyed Polyethylene Terephthalate Yarns

Tavanaie H., Ataeian A., Ghasemi L., Kargar Z.

Fibres & Textiles in Eastern Europe

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2007

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Vol. 15, no. 4 (63)

54--58

EN

Dope-dyed polyethylene terephthalate (PET) set yarns, which are usually used for the production of fabrics dedicated to manufacture car seats, have better light and washing fastnesses when compared with those dyed with conventional methods such as carrier or high temperature dyeing. It is the aim of this paper to compare the properties of false twist-textured super bright, semi-dull, grey and black dope-dyed PET yarns including titanium dioxideand black pigments, respectively. X-ray diffraction (XRD) and DSC showed that the above mentioned additives lead to a rather looser microstructure. The loose structure exerted less resistance against the torsional and bending forces acting during the heat-setting of twisted yarn in texturing. The highest degree of crystalinity was observed for the super bright yarn. Titanium dioxide and black pigments led to an increase in the coefficient of friction of the false twist textured yarns. As a result of the additives, bulk and stretch ability of the textured PET yarn improved and its twist liveliness increased. Both the effects of additives on the fine structure as well as the coefficient of friction were held responsible for the differences seen as a result of dispersing titanium dioxide and black pigments in PET.

PL

Barwione w masie włókna PET, stosowane zazwyczaj do produkcji tkanin na tapicerkę samochodową, wykazują lepszą trwałość przy praniu i odporność na działanie światła niż włókna barwione konwencjonalnie. Badania XRD i DSC wykazały, że te włókna, które zawierały dodatki, posiadały raczej luźniejszą mikrostrukturę, co prowadzi do mniejszej odporności na siły skręcające i gnące, działające podczas stabilizacji termicznej teksturowanych przędz. Najwyższy stopień krystaliczności zaobserwowano dla włókien z połyskiem. Dwutlenek tytanu i czarny pigment prowadzą do wzrostu współczynnika tarcia przy teksturowaniu. Jako wynik zastosowania dodatków, poprawia się puszystość i podatność na rozciąg przędz PET i wzrasta żywotność skrętu. Stwierdzono, że wszystkie obserwowane zmiany zostały wywołane dodatkiem tlenku tytanu i czarnego pigmentu do matrycy polimerowej PET.

3

The fine structure of marine hydrophysical fields and its influence on the behaviour of plankton : an overview of some experimental and theoretical investigations

Druet C.

Oceanologia

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2003

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No. 45 (4)

517-555

EN

This article is an overview which presents in brief some of the results of research done in the last 20 years on the structure and dynamics of intermittent fine structure in the euphotic zone of the sea and its effect on the behaviour of marine plankton. The introduction provides a general characterisation of this structure and its relations with the plankton concentration field. Chapter 2 covers turbulent mixing processes in layers of homogeneous fine structure, and discusses the dynamic interactions of these layers and how these affect the behaviour of marine phyto- and zooplankton. The principal conclusions, in brief, are that the current state of knowledge, not only of intermittent fine structure itself and its dynamic transformations, but also of the influence of these processes on the behaviour of marine plankton, is today still a long way from permitting an accurate description of reality. Moreover, both empirical investigations (in situ and in the laboratory) and mathematical modelling, despite the quite advanced stage that the latter has reached, need to be continued. For this reason the prime aim of this article is to show up the gaps in our knowledge which future research in this complex, interdisciplinary area of oceanography should attempt to fill.

4

Spin-orbit coupling effects in ozone depletion spectroscopy

Minaev B., Bilan E.

Bulletin of the Polish Academy of Sciences. Chemistry

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2001

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Vol. 49, No. 2

133-164

EN

The structure of halogen oxides, XO (X = Cl, Br, I), stability of their anions and the UV-visible absorption spectra of hypohalous acids, HOX, are studied by ab initio methods with account of spin-orbit coupling (SOC) effects. The unrestricted Hartree-Fock (UHF) method, multi-configuration self-consistent field (MCSCF) calculations with linear and quadratic response techniques and MRCI method have been implemented. The Breit-Pauli form of the SOC operator is used. NMR spectra of HOI, HOBr and IO~ species are predicted. Photodissociation of the HOX molecules, which is crucial for the catalytic ozone-destruction cycle, is critically reviewed and analyzed. The singlet-triplet (S-T) transition to the lowest triplet state T\(XlA1 —ť3 A") is responsible for the weak long-wavelength tail absorption which induces photodissociation of these molecules. These absorption bands (380, 450 and 460 nm for X = Cl, Br and I, respectively) have small cross section, about (4, 15 and 24)xlO cm , respectively, but still are important for dissociation process HOX —ť X + OH and ozone concentration, since the stratosphere is transparent for such radiation. The second, more intense band (305, 350 and 406 nm for X = Cl, Br and I, respectively) is produced by two overlapping S-S and S-T transitions. The first singlet-singlet transition, SQ — Si, is relatively weak; it is responsible for about 95% of the cross section in HOC1; in HOBr the SQ — T% transition to the second triplet state contributes to this absorption band much more (about 50%); in HOI this is mostly the So — TI absorption. This band is strongly enhanced in HOI molecule because of the T% - 84 SOC mixing and its wavelength is red-shifted. In order to check this assignment of very peculiar HOI spectrum, the ESR and UV spectral properties of IO radical have been calculated with the same approximation. A good agreement with the ESR spectrum for the calculated nuclear quadrupole coupling constant and SOC splitting makes credit to the accuracy of HOI spectral interpretation. The third, most intensive UV absorption band (242, 280 and 340 nm for X = Cl, Br and I, respectively) in hypohalous acids is determined by the O—X bond polarized S-S transition to the second singlet exited state (X A' —ť 2 A'). All excited states are dissociative. The SOC account is of crucial importance for the absorption cross section calculations of the HOX molecules in the UV-visible part of solar actinic flux and for their lifetime in lower stratosphere. Account of SOC effect is also very important for the lifetime prediction of the halogen oxides and their anions.