Optical properties of organic semiconductors based on erbium phthalocyanine complexes in the mid- and near-infrared spec
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PHOUS, VITREOUS, POROUS, ORGANIC, AND MICROCRYSTALLINE SEMICONDUCTORS; SEMICONDUCTOR COMPOSITES
Optical Properties of Organic Semiconductors Based on Erbium Phthalocyanine Complexes in the Mid- and Near-Infrared Spectral Regions I. A. Belogorokhov^, E. V. Tikhonov, M. O. Breusova, V. E. Pushkarev, L. G. Tomilova, and D. R. Khokhlov Moscow State University, Moscow, 119899 Russia ^e-mail: [email protected] Submitted January 16, 2007; accepted for publication March 13, 2007
Abstract—The transmittance spectra of erbium phthalocyanine complexes in the mid- and near-infrared wavelength regions are studied. A detailed identification of the transmittance lines is presented for three types of phthalocyanine complexes. Data on the absorption of electromagnetic radiation at the wavelengths around 4I 1.5 µm due to the 4I13/2 15/2 intracenter transitions between the levels of the erbium ions incorporated into the samples are obtained. It is found that some of the mid-infrared absorption lines shift when the number of organic ligands is increased by a factor of 2 or 3. It is shown that the absorption coefficient at the wavelengths around 1.5 µm is equal to 27.5, 32.5, and 74 cm–1 for erbium monophthalocyanine, bisphthalocyanine, and triphthalocyanine, respectively. PACS numbers: 78.30.Jw DOI: 10.1134/S1063782607100156
1. INTRODUCTION Organic polycyclic compounds are promising materials for the production of semiconductor structures. One group of such structures is constituted by metal– phthalocyanine complexes (MPCs), heterocyclic compounds formed from phthalodinitrile derivatives. Phthalocyanines are interesting most of all due to the fact that, in contrast to polymers, such structures can be used to produce high-purity materials [1]. The purity of phthalocyanine structures may be so high that the concentration of impurity atoms is 1014–1016 cm–3. Semiconductor structures based on MPCs can easily be crystallized and sublimated and show high thermal and chemical stability: the materials are practically not destroyed in air at temperatures up to 400–500°C and most of them do not decompose in vacuum at temperatures up to 900°C. The MPC-based structures do not interact with strong acids (concentrated sulfuric acid) and strong bases. Only very strong oxidizers (bichromates or cerium salts) are capable of disintegrating the MPC molecules [2, 3]. Phthalocyanine complexes exhibit intrinsic photoluminescence in the region around 1000 nm; the photoluminescence is due to emission from the lowest singlet excitonic state [4]. In addition, it should be noted that phthalocyanines heavily absorb optical radiation in the visible spectral region. The ability of phthalocyanine rings to form compounds with every element from Group IA to Group VB of the Periodic Table offers a possibility of
controlling the optical and electrical properties of the molecules [1, 2]. It is the latter feature of phthalocyanine structures that has allowed the production of a broad class of synthesized organic semiconductor compounds containing rare-earth metal atoms
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