S. Nedilko

Comparable Structural and Luminescent Characterization of the La1-xEuxVO4 Solid Solutions Synthesized by Solid State and Co-Precipitation Methods

Luminescence properties of the two series of the La1-xEuxVO4 (x ranges from to 0.3) solid solutions synthesized by the solid state and co-precipitation methods were investigated.. Luminescence spectra of the investigated samples consist of narrow spectral lines caused by inner f - f electron transitions in the impurity Eu3+ ions. Excitation spectra consist of three main bands those correspond to different types of transitions in the investigated matrices. There are O - Eu3+ charge transfer transitions, band-to-band transitions in the matrix of the vanadate compounds and electron transitions in the VO43- vanadate anion. Dependences of the structure and luminescence properties on rate compositions and method of synthesis were studied. Origins of the observed differences between luminescence characteristics of the samples obtained by two different methods are discussed.

Study of Temperature Behavior of Luminescence Emission of LaVO4 and La1-xEuxVO4 Powders

The La1‑xEuxVO4 powders were synthesized by co-precipitation method. Emission spectra of the LaEuVO4 and La1‑xEuxVO4 powders consist of wide non-structural bands of the matrix emission and narrow spectral lines caused by inner f-f electron transitions in the Eu3+ ions, respectively. The both types of emission were studied within 8 – 300 K temperature range. Decomposition of spectra of the wide matrix emission on three bands has been carried out and temperature dependencies for each band were studied. Temperature behavior of the Eu3+ emission was investigated for lines assigned to different Eu3+ centres. Obtained dependencies are analyzed and discussed using proposed schemes of transitions in the VO43- groups and structure of the nearest surrounding of the Eu3+ emission centres.

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.

Effect of X-Rays and Power Laser Irradiation on the Complex Emission Centers in Dielectric Crystals

Irradiation effects on emission centers were studied with photo and X-ray luminescence investigations of alkali chromate crystals. The X-rays and powerful laser irradiations were used for this investigation. The irradiation effects were found to depend on a type and structure of emission centers. In the alkali Chromate crystals complex emission centers of a molecular type are formed by two weight centers: the Chromate oxyanion and the defect. The bond between weight centers can be broken under irradiation action. As established in our experiment, some types of the emission centers can decay or transform into other types under action of irradiation.

Synthesis and structure features of the Ca 1−2x Ce 2x Mo 1−x Ge x O 4 (0 ≤ x≤ 0.2) compounds

The Ca<inf>1−2x</inf>Ce<inf>2x</inf>Mo<inf>1−x</inf>Ge<inf>x</inf>O<inf>4</inf> (0 ≤ × ≤ 0.2) micro/nanosized powders were prepared by aqueous nitrate-tartrate sol-gel synthesis. The obtained samples were characterized by XRD analysis, SEM microscopy, and IR spectroscopy. It was shown, that increase of cerium concentration in the series of compounds does not lead to obvious changes in their crystal structure, but changes of unit cell lattice parameters was fixed. According to SEM analysis, particles of investigation molibdates have diameter 100–500 nm. Luminescence properties of the synthesized powders were studied. The photoluminescence spectra contain wide bands of matrix emission and narrow lines caused by f-f transitions in the RE³⁺ ions.

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.

Study of effects of rare earth impurities on structure of matrix emission of the lead tungstate crystals

The paper reports study of complex structure of matrix emission of undoped and RE-doped PbWO4 crystals. Decomposition of the spectra shows contributions of five components at 410, 485, 520, 565, 635 nm in emission of all the investigated samples. Their relative contributions depend on RE doping. Observed effects of RE doping are the same for the crystals with different RE impurities. Structures of luminescent centres are discussed taking into account studied effects of the impurity RE ions on spectral characteristics of the matrix emission.

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.

Crystal structure and luminescence of layered perovskites Sr 3 LnB III SnO 8 (B III = Sc, In)

The Sr₃LnInSnO₈ (Ln = La, Pr, Nd) and Sr₃LaScSnO₈ perovskites were synthesized and their structures have been determined by X-ray powder diffraction. The peculiarities of the structures and correlations composition - structure - luminescent properties have been discussed.