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Temperature Evolution of the Optical Absorption Edge in the A 2 BX 4 Type Compounds with Organic Cation
Author(s) -
Kapustianik V. B.
Publication year - 1997
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/1521-3951(199712)204:2<877::aid-pssb877>3.0.co;2-q
Subject(s) - absorption edge , raman spectroscopy , exciton , absorption (acoustics) , phase (matter) , absorption spectroscopy , analytical chemistry (journal) , chemistry , materials science , condensed matter physics , optics , band gap , physics , organic chemistry , optoelectronics , composite material
The temperature evolution of the optical absorption spectra of A 2 BX 4 type compounds with an organic cation have been analyzed. It was shown that the fundamental absorption edge in these materials possesses an exponential shape following the empirical Urbach rule due to the occurrence of the electron–(exciton–)phonon interaction. As an example, the parameters of the EPI have been determined for (NH 2 (CH 3 ) 2 ) 2 CuCl 4 crystals. Comparison of the obtained results with corresponding data for isomorphous compounds allowed to ascertain some total regularities characteristic of the EPI. Nonfulfilment of the Urbach rule in the incommensurate phase, particularly, was related to the considerable temperature dependence of the period and phase of the modulation. This conclusion is confirmed by data of Raman spectroscopy.