Effect of different strontium precursors on the growth process and optical properties of SrWO4 microcrystals

Abstract

In this paper, an experimental study was performed on the effect induced by different strontium precursors in the growth processes and optical properties of strontium tungstate (SrWO 4) microcrystals synthesized by the co-precipitation method. The structural behavior was analyzed by means of X-ray diffractions, Rietveld refinements, Fourier transform (FT)-Raman, and FT-infrared spectroscopies. X-ray absorption near-edge structure spectra performed at the W-L 1 and L 3 edges revealed the first coordination shell around the tungsten atoms is composed of four oxygens, i.e., existence of tetrahedral [WO 4 ] clusters inside the SrWO 4 structure. Field emission scanning electron microscopy (FE-SEM) images showed the presence of pitch and longleaf pine cone-like SrWO 4 microcrystals for most of the strontium precursors employed in the synthesis. Based on these FE-SEM images, a hypothetical crystal growth mechanism was proposed to explain the origin of these microcrystals. The optical properties were investigated by ultraviolet-visible spectroscopy and photoluminescence (PL) measurements at room temperature. The different optical band gap values found for this material, depending on the type of strontium precursor, were correlated with the existence of intermediary energy levels within the forbidden region. Finally, PL profiles were associated to the degree of distortions in tetrahedral [WO 4 ] clusters.

Hierarchical design and control of NaCe(WO4)2crystals: structural and optical properties

“…In addition to the abovementioned factors, other defects such as oxygen vacancies, pores and grain boundaries are also critical parameters that can change the band gap. An increased defect concentration can lead to the generation of many intermediary energy levels within the band gap 93 and consequently a decreased intensity of the absorption band. A theoretical approach and further calculations are necessary to fully elucidate exactly what factors determine in our case the energy level and define the intrinsic band structure of the materials.…”

Visible‐light‐driven photocatalytic degradation using Mn‐doped SrMoO4 nanoparticles

“…With Mn doping, E g greatly decreases from 3.90 to 2.90 eV. This is ascribed to strong hybrids among Mn, Mo and O when Mn substitutes at Mo sites …”

Synthesis and characterization of BaWO4:xTm3+,yPr3+ obtained by ultrasonic spray pyrolysis

“…The bandgap energy is estimated by αhv ∝ (hv−E gap ) 1/k [50][51][52], in which k is indicated for the different kinds of transitions, h is the Planck constant, α is the absorbance and v is the frequency. The k to tungstates have utilized a permitted direct electronic transition [53,54], so the results from BaWO 4 :xTm 3+ ,yPr 3+ samples were analyzed assuming k = 1/2, which is the expected value for such transitions and are shown in Fig. 5.…”