Physica B 403 (2008) 2561–2566 Specific features of absorption and DSC for the DEA-CuCl 4 nanoparticles incorporated into the PMMA polymer matrices K. Ozga a , M. Piasecki b , S. Tkaczyk b , B. Kapustianyk c , P. Bragiel b , A.H. Reshak d , M.G. Brik e , I.V. Kityk b,Ã a Institute of Biology and Biophysics, Technical University of Czestochowa, Czestochowa, Poland b Institute of Physics, J. Dlugosz University of Cz˛ estochowa, 42217 Cz˛ estochowa, Poland c Scientific Center of Low Temperature, Lviv, Ukraine d Institute of Physical Biology, South Bohemia University, Institute of System Biology and Ecology, Academy of Sciences, Nove Hrady 37333, Czech Republic e Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia Received 14 December 2007; received in revised form 18 January 2008; accepted 26 January 2008 Abstract Diethylammonium tetrachlorcuprate NH 2 (C 2 H 5 ) 2 CuCl 4 (DEA-CuCl 4 ) nanoparticles with sizes about 10 nm were synthesized and embedded into the PMMA polymer matrices. Using DSC temperature study a substantial influence of the polymer matrix on the phase transition temperatures was shown, reflecting a disturbing effect of principal 3d Cu–3p Cl metal–ligand charge transfer bands. Dependence of the absorption spectra on the nanocrystallites (NC) concentration was studied. It was established that an increase of the NC content results in spectral shift of CuCl 4 absorption bands. Explanation of this phenomenon has been suggested within a framework of first principle crystal field quantum chemical calculations. r 2008 Elsevier B.V. All rights reserved. Keywords: Nanocrystallites; Polymer nanocomposites; Optical materials 1. Introduction Single crystals of diethylammonium tetrachlorcuprate NH 2 (C 2 H 5 ) 2 CuCl 4 (DEA-CuCl 4 ) (space group P2 1 /n; lattice constants a ¼ 7.36 A ˚ ; b ¼ 15.025 A ˚ ; c ¼ 45.193 A ˚ [1]) and their derivatives attract considerable interest of researchers due to the substantial sensitivity of the CuCl 4 complexes to the surrounding environment, which allows for changing of optical properties of the DEA-CuCl 4 host. At room temperature these crystals are bright green and, since they possess a dozen of phase transitions [1], their color depends on temperature. Following Ref. [2], phase transitions observed at 311–330 K depend on the local environment of the Cu 2+ ions, which is manifested by about 50 nm spectral shift of the principal spectral bands. Their principal structure consists of the slightly deformed [CuCl 4 ] 2 tetrahedrons, the shape and size of which are very sensitive to the external field. As a consequence, slight variations of the corresponding local structure (induced by the external temperature) can produce significant changes in the soft mode condensation, responsible for phase transitions. Following the general consideration, one can expect the properties of the [CuCl 4 ] 2 units to be sensitive to the very low sizes (about 10 nm) of these nanocrystallites (NC), on the one hand, and to the surrounding matrices (in particular, polymers), into which these NC are embedded, on the other hand. In the present work, we focus on the DEA-CuCl 4 absorption spectra behavior depending on the content of the DEA-CuCl 4 NC. It is shown that changes of the effective nano-sheet surfaces (which occur when the NC concentration is varied) induce noticeable changes of the absorption spectra. ARTICLE IN PRESS www.elsevier.com/locate/physb 0921-4526/$ - see front matter r 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2008.01.027 Ã Corresponding author. E-mail address: i.kityk@ajd.czest.pl (I.V. Kityk).