E. V. Tikhonov

Photoluminescence in semiconductor structures based on butyl-substituted erbium phthalocyanine complexes

The study is concerned with the luminescence properties of ensembles of semiconductor structures containing organic phthalocyanine molecules with erbium ions as complexing agents. The photoluminescence spectra of the structures of the type of erbium monophthalocyanine, bisphthalocyanine, and triphthalocyanine are recorded. The photoluminescence peaks are detected at the wavelengths 888, 760, and 708 nm (and photon energies 1.4, 1.6, and 1.75 eV) corresponding to electronic transitions within the organic complexes. It is found that, when a metal complexing agent is introduced into the molecular structure of the ligand, the 708 nm luminescence peak becomes unobservable. It is shown that, in the bisphthalocyanine samples, the photoluminescence signal corresponding to transitions from the 4F9/2 level of erbium ions is enhanced.

Features of the spectral dependences of transmittance of organic semiconductors based on tert-butyl substituted lutetium phthalocyanine molecules

Vibronic properties of organic semiconductors based on tert-butyl substituted phthalocyanine lutetium diphthalocyanine molecules are studied by IR and Raman spectroscopy. It is shown that substitution of several carbon atoms in initial phthalocyanine (Pc) ligands with 13C isotope atoms causes a spectral shift in the main absorption lines attributed to benzene, isoindol, and peripheral C-H groups. A comparison of spectral characteristics showed that the shift can vary from 3 to 1 cm−1.

Features in the electronic structure and photoemission spectra of organic molecular semiconductors: The molecules of metal-phthalocyanines and PTCDA

The role of many-electron effects in the formation of electronic quasiparticle spectra in organic molecular semiconductors (OMS) is analyzed. Many-body perturbation theory, ab initio calculations of metal phthalocyanines and PTCDA molecules, and experimental photoemission spectra are applied to this analysis. It is shown that density functional theory (DFT) poorly reproduces the electronic spectra of OMS. The use of a hybrid functional method (HFM) provides precise reproduction of both valence and conducting bands, while the HOMO-LUMO gap remains underestimated. The correct gap width is obtained in both DFT and HFM, when it is calculated through ionization and affinity energies. It is shown that such an approach gives a formula for gap correction due to electron correlations, which is close to an expression derived from the GW approximation.

Vibronic and electric properties of semiconductor structures based on butyl-substituted mono-and triphthalocyanine containing erbium ions

The Raman spectra have been obtained and the temperature dependence of the conductivity of organic semiconductor structures based on butyl-substituted erbium monophthalocyanine and erbium triphthalocyanine has been studied. It has been found experimentally that the activation energy decreases dramatically and the Raman spectra exhibits four new peaks in the region of large Raman shifts as the molecular structure of the samples becomes more complicated.

Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green’s function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H2Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

Electronic and Spin Structure of Metal Phthalocyanines

We present the first-principles calculations of MPc molecules having the magnetic moment. Some of these molecules contain the magnetic 3d-metal atom (MnPc, FePc, and CoPc), whereas others have the non-magnetic metal atom with an odd number of electrons (CuPc, AgPc, and GaPc). Calculations show that the density functional theory greatly decreases the HOMO-LUMO gap and the spin-splitting energy, comparing with hybrid functional results closely related to the many-electron theory. It is found that the HOMO-LUMO gap of MPc molecules shows moderate changes, while their spin-splitting energy is very sensitive to the localization of spin density and varies very significantly.

Vibronic states in organic semiconductors based on non-metal naphthalocyanine. Detection of heterocyclic phthalocyanine compounds in a flexible dielectric matrix

The vibronic properties of semiconductor structures based on non-metal naphthalocyanine molecules are studied using IR and Raman spectroscopy methods. New absorption lines in the transmission spectra of such materials are detected and identified. Three transmission lines are observed in the range 2830—3028 cm−1, which characterize carbon-hydrogen bonds of peripheral molecular groups. Their spectral positions are 2959, 2906, and 2866 cm−1. It is detected that the phthalocyanine ring can also exhibit its specific vibronic properties in the Raman spectra at 767, 717, and 679 cm−1. The naphthalocyanine molecule in the organic dielectric matrix of microfibers is described using IR spectroscopy. It is shown that the set of vibrations characterizing the isoindol group, pyrrole ring, naphtha group, and C-H bonds, allows an accurate enough description of the vibronic states of the naphthalocyanine complex in complex heterostructures to be made. The spectral range with fundamental modes, characterizing a naphthalocyanine semiconductor in a heterostructure, is 600–1600 cm−1. A comparison of the compositions of complex systems with a similar heterostructure containing lutetium diphthalocyanine demonstrated few errors.

Frequency dependences of the imaginary and real parts of the permittivity of organic semiconductors based on butyl-substituted erbium monophthalocyanine molecules

The frequency dependences of the imaginary and real parts of the permittivity of organic semiconductors based on butyl-substituted erbium monophthalocyanine have been obtained. The static permittivity and damping factor, which characterizes the relaxation processes in the ensemble of phthalocyanine complexes, have been determined by fitting these dependences in the dipole approximation.

Optical Properties of Organic Semiconductors Based on Erbium Phthalocyanine Complexes in the Mid- and Near-Infrared Spectral Regions

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 1.5 μm due to the 4I13/2 → 4I15/2 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.

Raman scattering in semiconductor structures based on monophthalocyanine and triphthalocyanine molecules incorporating erbium ions

Semiconductor structures of the type of butyl-substituted erbium monophthalocyanine and triphthalocyanine are studied by Raman spectroscopy. It is shown that, when the sandwich-like structure of the molecule incorporating two complexing atoms between the ligands is considered instead of the planar molecular structure with one ligand and one metal atom, a series of lines appears in the Raman spectrum. In this series, the wave numbers of the lines represent an arithmetic progression with the arithmetical ratio ∼80 cm−1. It is suggested that this feature is due to the larger number of organic molecules per metal atom in the triphthalocyanine complex, and the four Raman peaks at the frequencies 122, 208, 280, and 362 cm−1 are the manifestation of slight out-of-plane vibrations of the phthalocyanine ligands.