Optical Properties of Nematic Liquid Crystal Composites with Semiconducting Quantum Dots

The synthetic route to obtain stable composites of liquid crystal ZhK-777 with semiconductor quantum dots CdSe/CdS and CdSe/CdS/ZnS has been proposed. The dependents of fluorescence intensity of the composites on size and concentration of used quantum dots has been established. The shift of the luminescence band and decrease of its intensity has been observed both for liquid crystal and quantum dots. This effect indicates that quantum dots interaction with liquid crystals caused by a nonradiative excitation energy transfer from liquid crystal molecules to quantum dots. The dielectric spectroscopy of ZhK-777 and composites revealed that doping with quantum dots results in change of molecular relaxation frequencies in composites.

Study on the optical properties for the F-type color center in BeO crystal with first-principles

In this paper, we calculated the defect formation energy of oxygen vacancies with different charge states (0, +1, +2) in beryllium oxide crystal by using density functional theory (DFT). Based on defect formation energy, the positions of charge transition levels are obtained. However, there is a well-known problem that DFT will underestimate the band gap, which leads to the positions of charge transition levels are arguable. To obtain more accurate charge transition levels, we employ the hybrid functionals (HSE) to relieve the band edge problem, as well as use the finite-size corrections (FNV) to correct the defect formation energy. After obtaining the location of the charge transition level, we obtain a reliable description of the optical line shape of the F/F[Formula: see text] center containing electron–phonon coupling. The absorption spectra of the F center and F[Formula: see text] center peak at 7.1 eV and 6.3 eV, respectively. The luminescence band of the F center peaks at 4.7 eV. Furthermore, we speculate that the luminescence band near 3.7 eV is assigned to the F[Formula: see text] center.

SPECTROSCOPIC PROPERTIES OF SOLIDIFIED MELTS OF THE EuF3-CeF3-NaCl-KCl SYSTEM

The nature of the interaction in the EuF3-CeF3 system in the process of high-temperature (1050 °C) oxidation - reduction reaction was established by the methods of IR transmission spectroscopy, diffuse reflection spectroscopy and fluorescence spectroscopy. Here is a significant bathochromic shift to 480-485 nm band of blue luminescence of Eu(II) - containing phases, due to the 5d–4f electronic transitions, as well as the manifestation of orange-red luminescence of Eu(III) - containing phases due to 4f–4f electronic transitions in the range of 590–690 nm. There is a bathochromic shift of the IR bandwidth in the spectrum of the solidified salt melt as a result of dissolution of the fluoride system. Diffuse reflection spectra reveal changes in the composition of the phases that dissolve in the salt melt due to exchange reactions. The wide absorption band in the UV range gives way to a negative absorption band consisting of two peaks due to luminescence. The almost complete disappearance of the band of 4f–4f transitions in Eu(III) in the near-IR range of the spectrum is evidence of its entire reduction in the chloride melt to Eu(II). The character of the luminescence spectra of solidified salt melts also changes in comparison with the initial sample of the EuF3-CeF3 system, namely, the luminescence band of Ce3+ ions disappears, and the luminescence band of Eu2+ ions at 430–440 nm becomes narrow and highly intensive. The luminescence band of Eu3+ ions in the orange-red region of the spectrum disappears completely. Thus, Eu2+ ions become dominant in the formation of the spectral picture of the solidified salt melt, which is evidence of the completion of the redox process in the system.

SOL-GEL PROCESSED SIO2-AL2O3 XEROGELS: SYNTHESIS AND LUMINESCENT PROPERTIES

SiO2-Al2O3 xerogels with various Si : Al ratios were synthesized via sol-gel method (two kinds of synthetic procedures were used) and characterized by means of elemental analysis, XRD, thermogravimetry and IR spectroscopy. No losses of precursors were found during the synthesis and the introduced components are quantitatively transferred from the initial mixture to the composition of the formed samples.The position of the luminescence band in the 300–500 nm region depends on the wavelength of the exciting light, time of gel maturation and the drying temperature, which is the manifestation of the influence of the structure of units in xerogels on the luminescent properties.