Experimental and Theoretical Investigations of Electronic Structure and Photoluminescence Properties of β-Ag₂MoO₄ Microcrystals

Abstract

In this paper, we investigate a correlation between theoretical calculations and experimental data to explain the electronic structure and optical properties of silver molybdate (β-Ag 2 MoO 4 ) microcrystals synthesized by the microwave-assisted hydrothermal method. X-ray diffraction, Rietveld refinement, and micro-Raman spectroscopy confirmed that these microcrystals crystallize in a spinel-type cubic structure. Field-emission scanning electron microscopy images revealed that the processing temperatures influence in the final shape of microcrystals. Optical properties were analyzed by ultraviolet−visible diffuse reflectance spectroscopy; the increase in the optical band gap energy (E gap ) (from 3.24 to 3.31 eV) with processing temperature is associated with the reduction of intermediary energy levels. First-principles quantum mechanical calculations based on the density functional theory at the B3LYP level were conducted. The calculated band structure revealed an indirect E gap of approximately 4.00 and 3.34 eV for the β-Ag 2 MoO 4 without and with the formation of defects, respectively. Theoretical calculations based on density of states and electron density maps were employed to understand the polarization phenomenon induced by structural defects in the β-Ag 2 MoO 4 crystals. Finally, photoluminescence properties at room temperature of β-Ag 2 MoO 4 microcrystals were explained by the charge-transfer mechanism involving tetrahedral [MoO 4 ] clusters.

Understanding the Phosphorylation Mechanism by Using Quantum Chemical Calculations and Molecular Dynamics Simulations

“…It depends on all of the coordinates of the system, which provides a more efficient sampling method than a geometrical reaction coordinate to better reflect the activities of the compounds. 46 Table 1 lists the E gap values in the six compounds. It can be seen that E gap in the phosphorylated residues are lower than that of non-phosphorylated Ser, Thr, and Tyr, which indicates that the electron transfer may occur more easily in the phosphorylated residues than non-phosphorylated ones.…”

Phonon properties of β-Ag2MoO4: Raman spectroscopy and ab initio calculations

“…Molybdate compounds are important materials for a range of technological applications due to their chemical stability [1,2], which make them suitable to be used in electrochemical devices [3], microwave-based devices [4], optical fibers [5], light emitters [6,7], scintillators [8], sensors [9], and catalysts [10]. In particular, the silver molybdate compound (Ag2MoO4) belongs to the class of molybdates and tungstates with A2 + B 6+ O4 formula, where A is univalent metal and B is molybdenum or tungsten.…”

“…The silver molybdates can be obtained by different methods of synthesis [12][13][14][15][16][17][18][19][20][21][22][23][24][25] in various morphologies [26,15,27,28,7,29,20,30], which make this compound the subject of several investigations, including the study of structural transitions by means of differential thermal analysis (DTA) [2], X-ray diffraction (XRD) [27,6], Raman spectroscopy [1,27,6,31], surfaceenhanced Raman spectroscopy [27,28] and absorption and emission spectroscopy [6,28,32,7]. However, the room temperature structure of the Ag2MoO4 crystal exists in two different forms namely as α-Ag2MoO4 (tetragonal) and β-Ag2MoO4 (cubic) [33].…”

“…However, the room temperature structure of the Ag2MoO4 crystal exists in two different forms namely as α-Ag2MoO4 (tetragonal) and β-Ag2MoO4 (cubic) [33]. The structure of β-Ag2MoO4 was originally examined by the X-ray diffraction method [34], in a cubic spinel-like structure with lattice parameter a = 9.322 Å [6,35,34]. A ferroelastic phase transition in the spinel-like structure of the molybdate is expected to occur at high temperatures [31].…”

Structural refinement, Raman spectroscopy, optical and electrical properties of (Ba1−xSrx)MoO4 ceramics

“…Depending on the nature of the substituted ions into tetragonal lattice in the host matrix of scheelite materials enhances the intensity of PL spectra and shift towards the shorter wavelength region at room temperature [21,22]. The existence of localized energy levels in between conduction and valence band has a significant effect on the values of the band gap [23]. The thermodynamics and enthalpies of formation of tungstates and molybdate materials depends on the ionic radii, pH and alkaline earth metals which is highest in BaWO 4 and BaMoO 4 compounds compare to other alkaline metals followed by strontium molybdate SrMoO 4 (SMO), CaMoO 4 (CMO) etc., its kinetics of formation governs the transport of matter during heating process [24][25][26].…”