P. P. Pershukevich

Blue Photoluminescence of Oxidized Films of Porous Silicon

It is found that the films of n+-type porous silicon of low (10–50%) porosity exhibit photoluminescence in the region 400–500 nm after a 5-month storage in an air atmosphere. The spectrum of blue photoluminescence of the least porous but strongly oxidized films has maxima at 417, 435, and 465 nm. The same spectrum structure manifests itself upon the introduction of an Er3+- and Yb3+-containing complex. The mechanisms of blue photoluminesence are discussed.

The fluorescence and electronic structure of phenyl-substituted tetraazachlorin molecules

The effect of the addition of phenyl groups to pyrrole rings of tetraazachlorins, a new class of tetrapyrroles, on the photophysical properties and electronic structure of the molecules has been investigated by a complex of experimental and theoretical methods. Characteristics of fluorescence at 293 and 77 K have been determined for phenyl-substituted tetraazachlorins. The objects of this study include unsubstituted tetraazaporphine. The introduction of phenyl groups affords a marked increase in the fluorescence quantum yield. For tetraazaporphine and phenyl-substituted tetraazachlorins, fluorescence buildup occurs as the temperature is decreased from 293 to 77 K, but to a lesser extent than for tetraazachlorins having no phenyl groups, which were earlier studied by the authors. The fluorescence buildup mechanism is discussed. The singlet oxygen generation quantum yield has been determined for the tetrapyrroles examined. This characteristic increases upon tetrapyrrole is phenylation. The electronic structure and absorption spectra of unsubstituted porphine and chlorin, tetraazaporphine, tetraazachlorin, octaphenyltetraazaporphine, and tetramethylhexaphenyltetraazachlorin have been calculated by the INDO/Sm method (original modification of the INDO/S method) with molecular geometry optimization using DFT. The results of the quantum-chemical calculation of the absorption spectra are in good agreement with experimental data for transitions to the lowest excited electronic states Qx(S1) and Qy(S2).

SPECTRAL-LUMINESCENT PROPERTIES OF SUBSTITUTED TETRAAZACHLORIN AND OF ITS ZINC COMPLEX

The spectral, energy, kinetic, and polarization characteristics of fluorescence of di(tert-butylbenzo)barrelene-substituted tetraazachlorin and of its zinc complex in solutions are measured. The results are compared with similar data for tetraazaporphin and unsubstituted chlorin. Quenching of the fluorescence of the tetraazachlorins under investigation is noted.

Luminescence of an erbium- and ytterbium-containing complex in porous silicon films

Er3+ and Yb3+ ions are introduced into porous silicon films, stabilized by oxidation in an oxygen plasma, in the form of a gadolinium oxychloride-based luminophor by means of thermal diffusion. An investigation is made of the luminescence and photoexcitation spectra of samples with Er3+ (10 and 30 wt.%), Yb3+ (10 wt.%), and Er3, Yb3++ (10 wt.% each). It is shown that the intense IR luminescence (1.00 and 1.54 μm) is caused by cross-relaxation effects. The most effective excitation of the luminescence has been observed in the UV absorption band of the porous silicon.

Spectroscopic properties of polycrystals of supramolecular europium complexes with bathophenanthroline

Nanostructured supramolecular complex of europium(III) with bathophenanthroline (bphen), with detonation synthesis nanodiamonds (NDs) used as a structure-forming element, has been synthesized for the first time. The characteristics of the Eu(bphen)2(NO3)3 complex and the supramolecular complex with NDs, ND–Eu(bphen)2(NO3)2, are studied and compared using scanning electron microscopy (SEM), luminescence spectroscopy, IR spectroscopy, and electron-spin resonance (ESR) spectroscopy. The luminescence quantum yields of the complexes are estimated by the relative method using a β-diketonate complex of europium (III) with tris(thenoyltrifluoroacetone) and 1,10-phenanthroline (Eu(TTA)3phen) as a reference. It is found that the ND–Eu(bphen)2(NO3)2 supramolecular complex has a higher photoresistance than the complex without NDs and no worse thermal stability (up to a temperature of +150°C).

FLUORESCENCE OF SUBSTITUTED TETRAAZABACTERIOCHLORIN

The spectral, energy, and polarization characteristics of the fluorescence of substituted tetraazabacteriochlorin in solution have been obtained. On the basis of the polarization spectrum, the electronic absorption spectrum is interpreted. The quenching of the fluorescence of bacteriochlorin on substitution of methine bridges by aza bridges is noted.

The effect of annulation of benzene rings on the photophysics and electronic structure of tetraazachlorin molecules

The photophysics and electronic structure of tribenzotetraazachlorins (H2, Zn, and Mg), which are novel analogues of phtalocyanines, have been studied experimentally and theoretically. At 293 K, the electronic absorption, fluorescence, and fluorescence excitation spectra are recorded and the fluorescence quantum yield and lifetime, as well as the quantum yield of singlet oxygen generation, are measured; at 77 K, the fluorescence, fluorescence excitation, and fluorescence polarization spectra are recorded and the fluorescence lifetime values are measured. The dependences of the absorption spectra and photophysical parameters on the structure variation are analyzed in detail. Quantum-chemical calculations of the electronic structure and absorption spectra of tribenzotetraazachlorins (H2, Mg) are performed using the INDO/Sm method (modified INDO/S method) based on molecular-geometry optimization by the DFT PBE/TZVP method. The results of quantum-chemical calculations of the electronic absorption spectra are in very good agreement with the experimental data for the transitions to two lower electronic states.

Concentration Effects Manifesting Themselves in the Luminescence of Tm3+ Ions in an Oxychloride Matrix

We investigated the luminescence characteristics of Tm3+ ions depending on their concentration in an oxychloride matrix. We measured luminescence spectra, luminescence excitation spectra, concentration dependences of the intensity and kinetics of various luminescence bands of rare‐earth ions of the visible and IR ranges at different excitation wavelengths. We carried out calculations of the concentration dependences of the quantum yield of luminescence: total and individual spectral bands. The cross‐relaxational nature of concentration effects in the luminescence of rare‐earth ions is discussed.

Luminescence of Tm3+ Ions in Yttrium Oxide

The concentration and temperature dependences of the blue luminescence intensity of the Tm3+ ion in yttrium oxide under UV and IR excitation have been measured. We made a proposal that the main role in the formation of these dependences is played by the interionic cross relaxation of excited states of Tm3+; the presence of admixed secondary rare‐earth ions can strongly influence the shape of the temperature dependence of the anti‐Stokes luminescence intensity, displacing the position of its maximum. It is shown that the quenching action of admixtures under Stokes and anti‐Stokes excitation shows up differently because of the differences in the mechanisms of population of the luminescent level.

Luminescence of porous silicon films with an europium-containing complex

We obtained porous silicon films modified at room temperature by an Eu3+-containing polymer complex. The most intense photoluminescence of Eu3+ implanted in the porous silicon was observed at the wavelengths of 611, 618, 691, and 704 nm. In this case, the intensity of the intrinsic photoluminescence of strongly irradiated specimens of porous silicon decreased, while the intensity of weakly emitting films multiply increased. An investigation of the photoexcitation spectra made it possible to establish the effect of Eu3+-containing complexes on the mechanism underlying the excitation of photoluminescence of porous silicon.