An ab initio modelling for pristine and defect-induced emissions from NaCe(WO 4 ) 2 : a potential material for solid-state lighting application

Tetragonal NaCe(WO 4 ) 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 CeO 8 dodecahedra (c.a. CeO 7 and CeO 6 ). It has been observed from photoluminescence spectra that the synthesised samples exhibit intense emission at 435 nm due to 5 d –4 f transition of Ce 3+ within CeO 8 dodecahedra, whilst emission at 485 nm is assigned for same transition within CeO 7 . CeO 6 provides two emissions at 451 and 520 nm. Herein, we have identified that CTAB plays an important role in the formation of CeO 7 and CeO 6 . In contrast to earlier ethylene-diamine–tetra-acetic acid-assisted NaCe(WO 4 ) 2 with predominant green emission, our samples exhibit strong violet emission indicating less formation of CeO 7 and CeO 6 by CTAB. Herein, our ab initio calculation using density functional theory reveals that valence and conduction bands comprise O 2 p and O 2 p –Ce 5 d orbitals, respectively, whilst Ce 5 d z 2 and 5 d yz , 5 d xz orbitals mostly facilitate 5 d –4 f transition within CeO 7 and CeO 6 . Commission Internationale de l'Elcairage coordinates are found in violet region with correlated colour temperature ~ 6491 K indicating that CTAB-assisted hydrothermally synthesised NaCe(WO 4 ) 2 can be a potential material for cold solid-state lighting application. Graphical abstract