Evolution of photoluminescence as a function of the structural order or disorder in CaMoO4 nanopowders

Abstract

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.

Synthesis of CaMoO4 hierarchical structures via a simple slow-release co-precipitation method

“…All the Raman-active modes of CaMoO 4 crystals in this work are in good agreement with previously literature [23]. It is clear to note that the Raman spectrum shows sharp wellresolved bands, indicating that the as-prepared CaMoO 4 possess a good degree of crystallization with long-and short-range orders and few defects [22]. Based on the analysis of the above, there is no doubt that CaMoO 4 with tetragonal scheelite structure was successfully synthesized in our experiments.…”

“…The strong absorption band situated at 812 cm −1 is related to the antisymmetric stretching vibrations in the MoO 4 clusters, which correspond to the IR active v 3 E u modes [8,21]. The weak absorption band located at 430 cm −1 is due to A u mode of antisymmetric bending vibrations involved in the Mo O bonds [22]. The other wake absorption band centered at 408 cm −1 attribute to v 4 E u mode of Mo O bending vibration [23,24].…”

Photoluminescent Properties of CoMoO<sub>4</sub> Nanorods Quickly Synthesized and Annealed in a Domestic Microwave Oven

“…PL spectra observed for all powders show a maximum emission located at 450 nm (blue region of the electromagnetic spectrum). According to Wu et al [32,33], the emission band shape might be explained by considering the Jahn-Teller active vibration modes of T 2 symmetry that influence the [MoO 4 ] 2− complex anion of slightly distorted tetrahedral symmetry which leads to a strucured absorption band for the A 1 -T 1(2) transition. t clusters.…”

Effect of process parameters on photophysical properties and barium molybdate phosphors characteristics

“…More ordered structures are expected to have a higher gap energy than structures less ordered because defects promote intermediate stages between acceptor and donator bands which decreases gap energy values [26]. According to this theory, gap data calculated for BMO-2 (material is more ordered) and BMO-4 heat treated at 400 1C (material is more disordered), were 4.35 and 3.85 eV for BMO-2 and BMO-4 samples, respectively.…”

“…For a perfect crystal, the firstorder Raman phonon spectrum consists of narrow lines that correspond to Raman-allowed zone center (Γ-point) modes definite polarization selection rules. However, for disordered crystals, the following features are anticipated in the phonon spectrum: (1) a broadening of the first-order Raman lines; (2) the activation of forbidden Raman phonons; (3) the appearance of broad Raman bands reflecting the phonon density of states; (4) frequency shifting of some peaks proportional to the dopant element concentration (i.e., one-phonon-like behavior); and (5) the splitting of a number peaks involving different elements that share the same lattice site (i.e., two-phonon-like behavior) [25,26]. For ordered crystals analyzed by Raman spectrum with characteristic narrow lines, the maximum FWHM values from Bragg reflections and Raman bands were calculated and are listed in Table 4.…”