The Role of Short-Range Disorder in BaWO₄ Crystals in the Intense Green Photoluminescence

Abstract

An intense and broad visible photoluminescence (PL) band was observed at room temperature in short-range disordered BaWO 4 crystals. The scheelite crystalline BaWO 4 powders prepared by the polymeric precursor method and annealed at different temperatures were structurally characterized by means of X-ray diffraction and Fourier transform (FT) Raman spectroscopy measurements. Quantum-mechanical calculations indicated that the disorder at short range only of Ba atoms in the BaWO 4 lattice has a very important role in the charge transfer involved in the intense green PL emission. This indication was detected and confirmed by means of FT Raman spectroscopy measurements. The experimental and theoretical results are in good agreement, both showing the specific type of structural disorder that is the most favorable condition for generating the most intense green PL emission in the scheelite BaWO 4 lattice.

Synthesis, Characterization, and Low Temperature Sintering of Nanostructured BaWO4for Optical and LTCC Applications

“…Besides this strong band, a medium intense band can be seen in the region 632 cm −1 which can be attributed to W-O antisymmetric stretching vibrations. Our results match well with the early reported literatures [37,42].…”

“…The calculated optical band gap is also illustrated in Figure 6. The band gap of the sample is found to be 4.1 ev, which is exactly matching with the value reported by Cavalcante et al [9], Anicete-Santos et al [42], and Tyagi et al [44] for BaWO 4 . The present obtained value is lower than that reported by Lima et al [11] which is 5.67 eV.…”

“…All the observed Raman modes are the characteristics of a scheelite tetragonal [9,[40][41][42]. The internal modes ] 1 ( ), ] 2 ( ), ] 3 ( ), and ] 4 ( ) were observed at 924, 842, 790, 361, 345, and 326 cm −1 .…”

“…In order to reduce the structural disorder, the sample was annealed at 700 ∘ C for 1 hour, and again the PL spectrum was recorded as the fact that highly disordered and highly ordered structures at short range are not favorable to intense PL emission [42]. The emission spectrum of annealed sample is as in Figure 10(b).…”

Synthesis and morphological transformation of BaWO4 crystals: Experimental and theoretical insights

“…BaWO 4 is a semiconductor that belongs to the family of scheelites with crystallized tetragonal structures having the space group I4 1 / a and symmetry C 4h 6 , in which Ba atoms are coordinated to eight O atoms, while W atoms have tetragonal coordination of O atoms; thus, the building blocks of the BaWO 4 crystal are deltahedral [BaO 8 ] and tetrahedral [WO 4 ] clusters [14,[25][26][27][28][29][30]. Distortions of these clusters caused by the deformations of W-O and Ba-O bond distances as well as by tilting of O-W-O and O-Ba-O bond angles have a significant effect on their geometry, surface structure, and related properties [14].…”