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_z² and 5d_yz, 5d_xz 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 ~ 6491 K indicating that CTAB-assisted hydrothermally synthesised NaCe(WO₄)₂ can be a potential material for cold solid-state lighting application. [ABSTRACT FROM AUTHOR]