A complimentary combination of experimental work and first principle calculations, based on the Density Functional Theory (DFT) method, has been used to increase our limited understanding of the enhanced photocatalytic activity of PbMoO 4 powders with predominant (111), (100), (011), and (110) facets.In this work, PbMoO 4 powders were prepared by the co-precipitation method and processed on a hydrothermal reactor at 100 o C/10 minutes. The variation of different types of modifier such as acetylacetone (acac) or polyvinylpyrrolidone (PVP) is found to play a crucial role in controlling the particle size and morphology of products and their photocatalytic properties.The structure and morphology of these crystals were characterized by X-ray diffraction (XRD), micro-Raman (MR) spectroscopy, field-emission gun scanning electron microscopy (FEG-SEM), and ultraviolet visible (UV-vis) absorption spectroscopy. Furthermore, the assynthesized PbMoO 4 micro-octahedrons without presence of (001) surface exhibit enhanced activity for the photodegradation of rhodamine B (RhB) under ultraviolet-visible light irradiation.Based on the theoretical and experimental results, we provide a complete assignment of the micro-Raman spectra of PbMoO 4 , while a growth mechanism for the formation of PbMoO 4 micro-octahedrons was systematically discussed, and a schematic illustration of the probable formation of morphologies in the whole of the synthetic process was also proposed, which reveals that the high photocatalytic activity is attributed to the absence of (001) facet.

CaMoO 4 nanopowders were prepared by the complex polymerization method. The materials were characterized by x-ray diffraction ͑XRD͒ and by Fourier transform infrared, Raman, and optical reflectance spectroscopies. The data revealed the presence of crystalline scheelite-type phase CaMoO 4 and the absence of additional phases. The surface morphology was monitored by high-resolution scanning electron microscopy ͑HR-SEM͒. The HR-SEM and XRD characterizations both revealed a tendency for the particle size to increase with rising treatment temperatures. The disordered nanopowders showed strong emission of photoluminescence, which dropped to minimal levels in the ordered nanopowders. These differences in the photoluminescence of disordered and ordered nanopowders were attributed to complex cluster vacancies.

The preparation of nanometer-sized structures of zinc oxide (ZnO) from zinc acetate and urea as raw materials was performed using conventional water bath heating and a microwave hydrothermal (MH) method in an aqueous solution. The oxide formation is controlled by decomposition of the added urea in the sealed autoclave. The influence of urea and the synthesis method on the final product formation are discussed. Broadband photoluminescence (PL) behavior in visible-range spectra was observed with a maximum peak centered in the green region which was attributed to different defects and the structural changes involved with ZnO crystals which were produced during the nucleation process.

Ag 2 CrO 4 microcrystals were synthesized Q3 using the co-precipitation method. These microcrystals were characterized through X-ray diffraction (XRD) with Rietveld analysis, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) with energy-dispersive spectroscopy (EDS), micro-Raman (MR). XRD patterns and Rietveld refinement data showed that the material exhibits an orthorhombic structure without any deleterious phases. FE-SEM and TEM micrographs revealed the morphology and the growth of Ag nanoparticles on Ag 2 CrO 4 microcrystals during electron beam irradiation. These events were directly monitored in real-time. Their optical properties were investigated using ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy that allowed the calculation of the optical band gap energy. Theoretical analyses based on the density functional theory level indicate that the incorporation of electrons is responsible for structural modifications and formation of defects on the [AgO 6 ] and [AgO 4 ] clusters, generating ideal conditions for the growth of Ag nanoparticles.

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In this article, the synthesis by means spray pyrolysis method, of the CaMoO4 and rare earth cation (RE 3+)-doped CaMoO4:xRE 3+ (RE 3+ = Eu 3+ , Tb 3+ , and Tm 3+ ; and x= 1%, 2%, and 4% mol) compounds is presented. The as-synthesized samples were characterized using x-ray diffraction (XRD), Rietveld refinement, field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy. To complement and rationalize the experimental results, first principle calculation, at density functional theory level, have been performed to analyze the band structure and density of states. In addition, a theoretical method based on the calculations of surface energies and Wulff construction was applied to obtain the morphology transformation of the CaMoO4 and CaMoO4:RE 3+ microstructures. The experimental morphologies can be observed in the FE-SEM images. The PL behavior of the co-doped samples exhibited well-defined bands in the visible region. The samples with 2% and 4% of RE 3+ released white emission according to the chromaticity coordinates (0.34, 0.34) and (0.34, 0.33), respectively. Present results provide not only a deep understanding of the structure-property relationships of CaMoO4-based phosphor, but also can be employed as a guideline for the design of the electronic structure of the materials and the fabrication of photo-functional materials with optimal properties, which allows for the modeling of new phosphors for applications in solid-state lighting.

behavior and structural properties with various practical applications in different fields that involve chemical and biological applications, sensor and detector, display devices, light emitting diodes (LEDs), optical fibers, scintillator materials, catalysis and lithium ion batteries [1-3]. Among these compounds, calcium molybdate, CaMoO 4 , is one of the most attractive members of this family due to its very interesting physical and chemical properties as well as electronic structure, their high luminescence intensity, good thermal and chemical stability and high density. These properties allow it to be a good host material for luminescent materials under ultraviolet (UV) and X-ray excitation [2,[4][5][6][7][8][9][10][11][12][13][14][15].CaMoO 4 presents a body-centered scheelite structure, which belongs to the tetragonal I4 1 /a space group and contains two formula units per primitive cell. In this crystal, the building blocks of this structure are the (MoO 4 ) and (CaO 8 ) clusters corresponding to the local coordination in which Mo cation is linked to four equivalent O anions to construct (MoO 4 ) tetrahedral clusters while the Ca cation forms (CaO 8 ) octahedral clusters and it shares corners with eight adjacent O anions in (MoO 4 ) tetrahedrons. In turn, (CaO 8 ) octahedral connect via its edges and form a 3D framework [16,17]. In particular, the optical behavior of CaMoO 4 is associated to the stability and luminescent properties of (MoO 4 ) tetrahedron cluster with strong absorption in the UV region due to the charge transfer from oxygen to metal.A plethora of synthetic routes was successfully used to obtain CaMoO 4 including the flux method. It has also been employed the Czochralski technique, floating zone-like technique, microemulsion process, citrate complex method, co-precipitation method, electrospinning process, chemical deposition, hydrothermal/solvo thermal routines, and microwave assisted techniques [7,13,[18][19][20][21][22][23][24][25][26][27][28][29][30][31].

The PbMoO 4 co-doped with Tm 3þ , Tb 3þ Eu 3þ with scheelita structure was synthesized by the sonochemical method. The photoluminescent properties, structural and color coordinates emitted by phosphors were investigated. The structural analysis of the crystal and the changes in lattice parameters confirm that the rare earth ions (RE 3þ) were successfully introduced into the host of the PbMoO 4. The relationship between energy gap (Egap) and the concentration of RE 3þ ions was also discussed, the Egap is significantly influenced by the degree of structural order-disorder present in the crystal lattice. The PbMoO 4 :RE 3þ shows light emission in green. Under UV excitation, Photoluminescence (PL) shows a broad band centered at 520 nm and smaller bands belonging to transitions of RE 3þ :