Yu. Hizhnyi

Electronic structure and luminescence mechanisms in ZnMoO4 crystals.

Calculations of the band structure, partial densities of states and optical spectra of permittivity, reflectivity and absorption of perfect ZnMoO(4) crystal were performed using the full-potential linear-augmented-plane-wave method. It is shown that the calculated reflectivity spectra reproduce the main features of corresponding experimental spectra in the fundamental absorption region. The bandgap value of ZnMoO(4) is estimated as E(g) = 4.3 eV. Peculiarities of luminescence excitation spectra corrected for near-surface losses and losses on reflectivity are discussed, taking into account the results of the calculations. It is found that the energy structure of the lower part of conduction band is manifested in the excitation spectra of the intrinsic luminescence. The excitation spectra in the region 4.3-8.0 eV are formed by band-to-band electronic transitions mainly within the molybdate groups MoO(4)(2-), whereas electronic states of Zn(2+) cations are not directly involved into the excitation processes. It is shown that the structure of the intrinsic luminescence excitation spectrum depends on the temperature and mechanisms of the structure modification are discussed.

Investigation of the luminescent properties of pure and defect lead tungstate crystals by electronic structure calculations

Abstract Luminescence and scintillation properties of lead tungstate PbWO4 crystals have been investigated intensively in the recent years due to potential use of these crystals as scintillation materials in high-energy physics. However, up to now there is no generally accepted explanation of the origin of luminescence in PbWO4. The electronic structure of possible luminescent centers is ab initio calculated in order to elucidate the centers of intrinsic and defect luminescence in PbWO4 crystals. The influence of oxygen vacancies and praseodymium impurities on the luminescent properties of lead tungstate crystals is investigated and discussed. Possible channels of luminescence excitation and emission in perfect and defective PbWO4 crystals are obtained on the basis of the electronic structure calculations.

Electronic structure and VUV spectroscopy of bismuth-containing phosphate-tungstate crystals

The origin of intrinsic luminescence and mechanisms of excitation energy transfer in undoped K₂Bi(WO₄)(PO₄) and K_6.5Bi_2.5W₄P₆O₃₄ crystals are revealed in complex experimental and computational studies. The photoluminescence (PL) properties are studied under the VUV synchrotron excitations. The electronic structures of the crystals are calculated using the FLAPW method. Calculations indicate different character of the density of electronic states in the lower parts of the Conduction bands of K₂Bi(WO₄)(PO₄) and K_6.5Bi_2.5W₄P₆O₃₄. The PL emission spectra of K₂Bi(WO₄)(PO₄) and K_6.5Bi_2.5W₄P₆O₃₄ reveal wide bands peaking near 540 and 620 nm respectively. The PL in both compounds is effectively excited in 3.7 - 8 eV region of excitation energies.

Synthesis, electronic structure and VUV spectroscopy of K 2 BiZr(PO 4 ) 3 Crystals

The polycrystalline samples of K₂BiZr(PO₄)₃ were synthesized by spontaneous crystallization method. The photoluminescence (PL) spectroscopy studies of K₂BiZr(PO₄)₃ are carried out under the VUV synchrotron excitations. The electronic structure of K₂BiZr(PO₄)₃ is calculated by the FLAPW method. The PL spectra of K₂BiZr(PO₄)₃ reveal two main components in the UV and visible spectral regions (peaking near 3.6 and 2.6 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.

VUV spectroscopy and electronic structure of Al(PO 3 ) 3 crystals

The photoluminescence properties of undoped Al(PO₃)₃ crystals synthesized by flux method are studied under VUV synchrotron excitations. The electronic structure of Al(PO₃)₃ crystals is calculated by the FLAPW method. The PL emission spectra of Al(PO₃)₃ reveal emission bands in the violet 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.

Synthesis and luminescence of Cr(III)-doped aluminum oxide/molybdate composites

The conditions of synthesis and luminescence characteristics of composites Al₂O₃:Cr³⁺/NaAl(MoO₄)₂:Cr³⁺ obtained from molybdate high-temperature solutions have been studied. The influence of the impurity Cr³⁺ ions on crystallization regions in the molten system Na-Al-Mo-O has been detected as a key factor of composite formation. The luminescence emission spectra of the composite exhibit two narrow lines at 692 nm (Al₂O₃:Cr³⁺) and 740.5 nm (NaAl(MoO₄)₂:Cr³⁺), which indicates that both components of the composite are doped with chromium.

Synthesis, structure and luminescence properties of KBi(MoO 4 ) 2 :Eu 3+

Solid solutions KBi(MoO₄)₂:Eu³⁺ have been prepared by solid state synthesis and characterized by powder X-ray diffraction. The structure of KBi(MoO₄)₂ represents 3D framework built up from MoO₄ and BiO₈ species, while potassium cation has been found to share one position with bismuth.

Electronic structure and luminescence mechanisms in M I M III (MoO 4 ) 2 molybdates

The mechanisms of intrinsic luminescence in several molybdate crystals of M^IM^III(MoO<inf>4</inf>)<inf>2</inf> (M^I = Li, Na, K; M^III =Bi, Y, Fe) type are revealed in complex experimental and theoretical studies. The luminescence spectroscopy studies under VUV synchrotron excitations are applied together with the electronic structure calculations carried out by the FLAPW method. Simultaneous analysis of diffuse reflectance and luminescence excitation spectra is used for determination of the energy gap (Eg) values of the crystals. It is found that the molybdate groups MoO<inf>4</inf>2− play dominant role in the processes of intrinsic luminescence in studied molybdate compounds.