Vitalii Chornii

Electronic Structure and Luminescence Spectroscopy of M'Bi(MoO4)2 (M' = Li, Na, K), LiY(MoO4)2 and NaFe(MoO4)2 Molybdates

The mechanisms of intrinsic luminescence in the set of molybdate crystals of MIMIII(MoO4)2 (MI = Li, Na, K; MIII =Bi, Y, Fe) type are revealed in complex experimental and theoretical studies. The luminescence spectroscopy under vacuum ultraviolet (VUV) synchrotron excitations is applied together with the electronic structure calculations carried out by the FLAPW method. The energy gaps (Eg) values of the crystals are determined in simultaneous analysis of diffuse reflectance and luminescence excitation spectra. It is found that the molybdate groups MoO42- play a dominant role in the processes of intrinsic luminescence in studied molybdate compounds

Structural Modification of Single-Layer Graphene Under Laser Irradiation Featured by Micro-Raman Spectroscopy

Confocal micro-Raman spectroscopy is used as a sensitive tool to study the nature of laser-induced defects in single-layer graphene. Appearance and drastic intensity increase of D- and D′ modes in the Raman spectra at high power of laser irradiation is related to generation of structural defects. Time- and power-dependent evolution of Raman spectra is studied. The dependence of relative intensity of defective D- and D′ bands is analyzed to relate the certain types of structural defects. The surface density of structural defects is estimated from the intensity ratio of D- and G bands using the D-band activation model. Unusual broadening of the D band and splitting of the G band into G− and G+ components with redistribution of their intensities is observed at high laser power and exposition. Position of the G+ band is discussed in relation with nonuniform doping of graphene with charge impurities. Simultaneous presence in the Raman spectra of heavily irradiated graphene of rather narrow G band and broaden D band is explained by coexistence within the Raman probe of more and less damaged graphene areas. This assumption is additionally confirmed by confocal Raman mapping of the heavily irradiated area.

Synthesis, Crystal Structure, Luminescence and Electronic Band Structure of K2BiZr(PO4)3 Phosphate Compound

The single crystals of langbeinite-related K2BiZr(PO4)3 have been obtained for the first time by spontaneous crystallization method from K-Zr-P-O-F molten system. The compound crystallizes in a space group P213 with cell parameter a = 10.30360 Å. The framework is built up from isolated Bi/ZrO6 octahedra connected together by PO4 units. For the two K+ cations two types of oxygen coordination numbers 9 and 12 are observed. The photoluminescence (PL) spectroscopy studies of K2BiZr(PO4)3 are carried out under the VUV synchrotron excitations. The electronic structure of K2BiZr(PO4)3 crystal is calculated by the FLAPW method. The PL spectra reveal two main components in the UV and visible spectral regions (peaking near 3.6 and 2.7 eV respectively). It is assumed that the UV PL component of K2BiZr(PO4)3 originates from transitions in ZrO6 polyhedra, while the visible one is related to Bi3+ ions in oxygen coordination.

Synthesis, Luminescence and Electronic Band Structure of Al(PO3)3 Crystals

The crystals of aluminium metaphosphate Al(PO3)3 are synthesized by flux method. The photoluminescence properties of Al(PO3)3 are studied under the vacuum ultra violet (VUV) synchrotron excitations. The electronic structure of Al(PO3)3 crystal is calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. The photoluminescence (PL) emission spectra of of aluminium metaphosphate reveal emission bands in the ultraviolet-blue and in the yellow-red spectral regions. Obtained results point to an active role of the electronic states of phosphate groups in the processes of intrinsic luminescence in Al(PO3)3 crystals.

Crystal Structure and Luminescence of Layered Perovskites Sr3LnInSnO8

The Sr3LnInSnO8 (Ln = La, Pr, Nd) layered perovskites were synthesized and their structures have been determined by X-ray powder diffraction. Luminescence properties of the synthesized polycrystalline compounds Sr3PrInSnO8 and Sr3NdInSnO8 were investigated. Photoluminescence spectra of Sr3PrInSnO8 substantially depend on excitation wavelength unlike Sr3NdInSnO8 compound. The correlations between peculiarities of the crystal structures and photoluminescence properties have been discussed.

Synthesis and Luminescence Properties of KBi(MoO4)2:Eu3+

Polycrystalline KBi(MoO4)2 has been grown from molten system K-Bi-Mo-O. Solid solutions KBi1-xEux(MoO4)2 (x = 0.001 - 0.100) have been prepared by solid state synthesis and characterized by powder IR spectroscopy, DTA analysis, X-Ray powder diffraction and luminescence spectroscopy. It was found that all investigated Eu3+-containing molybdates reveal intensive photoluminescence lines related to f-f electronic transitions in Eu3+ ions. The KBi1-XEuX(MoO4)2 crystals with low Eu3+ concentration reveal also intrinsic host luminescence under excitation in the ultraviolet (UV) spectral region at T = 4.2 K.