An ab initio modelling for pristine and defect-induced emissions from NaCe(WO4)2: a potential material for solid-state lighting application

Tetragonal NaCe(WO4)(2) with oxygen vacancy has been successfully synthesised by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal technique. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, etc. have been employed for detailed structural analysis, whilst oxygen vacancies, explored by Raman, FTIR and X-ray photoelectron spectroscopies, lead to distorted CeO8 dodecahedra (c.a. CeO7 and CeO6). It has been observed from photoluminescence spectra that the synthesised samples exhibit intense emission at 435 nm due to 5d-4f transition of Ce3+ within CeO8 dodecahedra, whilst emission at 485 nm is assigned for same transition within CeO7. CeO6 provides two emissions at 451 and 520 nm. Herein, we have identified that CTAB plays an important role in the formation of CeO7 and CeO6. In contrast to earlier ethylene-diamine-tetra-acetic acid-assisted NaCe(WO4)(2) with predominant green emission, our samples exhibit strong violet emission indicating less formation of CeO7 and CeO6 by CTAB. Herein, our ab initio calculation using density functional theory reveals that valence and conduction bands comprise O 2p and O 2p-Ce 5d orbitals, respectively, whilst Ce 5d(z)(2) and 5d(yz), 5dxz orbitals mostly facilitate 5d-4f transition within CeO7 and CeO6. Commission Internationale de l'Elcairage coordinates are found in violet region with correlated colour temperature similar to 6491 K indicating that CTAB-assisted hydrothermally synthesised NaCe(WO4)2 can be a potential material for cold solid-state lighting application.