Triple molybdate NaCaLa(MoO):xEr,yYb (x = y = 0, x = 0.05 and y = 0.45, x = 0.1 and y = 0.2, x = 0.2 and y = 0) phosphors were successfully synthesized for the first time by the microwave sol-gel method. Well-crystallized particles formed after heat treatment at 900 °C for 16 h showed a fine and homogeneous morphology with particle sizes of 2-3 μm. The structures were refined by the Rietveld method in the space group I4/a. The optical properties were examined comparatively using photoluminescence emission and Raman spectroscopy. Under excitation at 980 nm, the NaCaLa(MoO):0.1Er,0.2Yb and NaCaLa(MoO):0.05Er,0.45Yb particles exhibited a strong 525 nm emission band, a weaker 550 nm emission band in the green region, and three weak 655 nm, 490 nm and 410 nm emission bands in the red, blue and violet regions. The pump power dependence and Commission Internationale de L'Eclairage chromaticity of the upconversion emission intensity were evaluated in detail.

We report on the experimental and theoretical study of the near-field diffraction of optical vortices (OVs) at a two-dimensional diffraction grating. The Talbot effect for the optical vortices in the visible range is experimentally observed and the respective Talbot carpets for the optical vortices are experimentally obtained for the first time. It is shown that the spatial configuration of the light field behind the grating represents a complex three-dimensional lattice of beamlet-like optical vortices. A unit cell of the OV lattice is reconstructed using the experimental data and the spatial evolution of the beamlet intensity and phase singularities of the optical vortices is demonstrated. In addition, the self-healing effect for the optical vortices, which consists in flattening of the central dip in the annular intensity distribution, i.e., restoring the image of the object plane predicted earlier is observed. The calculated results agree well with the experimental ones. The results obtained can be used to create and optimize the 3D OV lattices for a wide range of application areas.

Rare earth fluorides are mainly obtained from aqueous solutions of oxygen-containing precursors. Probably, this method is simple and efficient, however, oxygen may partially be retained in the fluoride structure. We offer an alternative method: obtaining fluorides and solid solutions based on them from an oxygen-free precursor. As starting materials, we choose sulfides of rare-earth elements and solid solutions based on them. The fluorination is carried out by exposure to hydrofluoric acid of various concentrations. The transmission electron microscopy images revealed the different morphologies of the products, * I. A. Razumkova Fax: +73452597559 E-Mail: razumkova@list.ru [a]

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A noniterative approach to generation of binary phase holograms is applied for synthesizing complex optical vortex arrays. This approach does not use inverse Fourier analysis and allows one to obtain arbitrary optical vortex arrays with specified topological charges, which cannot be obtained using conventional fork-shaped gratings. A topological charge of individual optical vortices generated using binary phase holograms can be specified at a given spatial frequency, so that the equidistant array of optical vortices can be generated via illuminating a hologram by a beam with the zero topological charge. The results of the calculation are consistent with the experimental data, including those of the interferometric measurements. The approach also makes it possible to synthesize superimposed optical vortices, where an optical field represents well-ordered circular arrays of optical singularities. An unusual behavior of phase dislocations in superimposed structures is found. For two optical vortices of same reciprocal lattice vectors, but different topological charges, spatial distribution of singularities are reconfigured in a such manner that a couple of concentric circular arrays of singularities appear. The proposed binary phase holograms offer new opportunities for synthesizing the complex optical vortex light fields, which can find light-matter interaction-based applications.