Unexpected formation of scheelite-structured Ca_1−xCd_xWO₄ (0 ≤ x ≤ 1) continuous solid solutions with tunable photoluminescent and electronic properties

Abstract

Design of a solid solution with tunable functionality is an attractive strategy toward realizing novel devices with multi-functionalities. In this work, a series of CaCdWO solid solutions in the entire range 0 ≤ x ≤ 1 with tetragonal scheelite structure have been successfully prepared for the first time. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopies indicated that all the nanocrystals have a tetragonal scheelite structure without wolframite phase. Structural refinement data revealed that the lattice volume decreased with the replacement of Ca by Cd ions. UV-Vis diffuse reflectance spectra indicated that optical band gap reduced with the replacement of Ca by Cd ions. Scanning electron microscopic (SEM) images showed that morphologies of the nanocrystals changed with the chemical compositions. The structure evolution of the solid solutions was further investigated by high-resolution transmission electron microscopy (HRTEM). Moreover, the influence of chemical compositions on the photoluminescent and electric performance has been performed and discussed. The reported synthetic approach and findings reported here are important to understand the structure and structure-property relation of scheelite-structured tungstate and molybdate compounds, which has potential applications in the design of other kinds of novel functional materials.

Structural and Optical Properties of Ca0.9Cu0.01WO4 Solid Solution Synthesized by Sonochemistry Method at Room Temperature

“…Well-defined 796, 837, and 911 cm −1 peaks observed in the Raman spectra for both samples are consistent with those reported in the literature. 11 Moreover, on the one hand, the 911 cm −1 peak has been also correlated with the symmetric stretching of ←O− W−O→ bonds of the tetrahedral clusters. 11 On the other hand, the 339 and 397 cm −1 peaks observed in the Raman spectra have been associated to the symmetric and nonsymmetric bending vibrations of the CaWO 4 structure, respectively.…”

“…11 Moreover, on the one hand, the 911 cm −1 peak has been also correlated with the symmetric stretching of ←O− W−O→ bonds of the tetrahedral clusters. 11 On the other hand, the 339 and 397 cm −1 peaks observed in the Raman spectra have been associated to the symmetric and nonsymmetric bending vibrations of the CaWO 4 structure, respectively. Contractions and bending of Ca−O groups from [CaO 8 ] clusters have been reported in the literature, 21 in the region from 80 to 280 cm −1 .…”

“…10 Consequently, some transition-metal-doped compounds have received excellent attention, especially copper-doped compounds, because copper ions (Cu 2+ ) can be distorted in structure by the Jahn-Teller effect, allowing O 2p → Cu 3d electronic transitions to be favored in the excitation/recombination process. 11,12 In the last decades, the optical, magnetic, and semiconductor properties of materials containing copper ions have been associated with many applications. 13−15 In this context, antimicrobial, 16 photoluminescent, 17 catalytic, 18 magnetic, 19 and solar cell applications 20 have been reported.…”

“…However, rare-earth elements are relatively costly in comparison with other elements of the periodic table, which are promising for applications, because they exhibit great optical properties and no toxic or genotoxic effects . Consequently, some transition-metal-doped compounds have received excellent attention, especially copper-doped compounds, because copper ions (Cu 2+ ) can be distorted in structure by the Jahn-Teller effect, allowing O 2p → Cu 3d electronic transitions to be favored in the excitation/recombination process. , …”

Structure, electronic properties, morphology evolution, and photocatalytic activity in PbMoO4 and Pb1−2xCaxSrxMoO4 (x = 0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions

“…Continuous series of substitutional solid solutions can provide a variation in crystal structure and changes in the band gap values and optical properties, and an opportunity to understand the structure property relationship can thus be achieved [24] [25]. The design of a solid solution based on molybdate compounds is a promising strategy for developing novel materials [26], with the aim of improving their properties, and consequently expansion wider range of applications [27][28] [29]. In particular, Hallaoui et al [30] have studied the structural and optical properties as a function of composition x for Sr(1-x)PbxMoO4 solid solutions, showing that the photocatalytic activity of PMO and SrMoO4 is different despite the similarity of the structures.…”