Synthesis, Neutron Diffraction, and DFT Studies of NaLa(WO₄)₂: Yb³⁺/Er³⁺; NIR Induced Green Fluorescent Bifunctional Probes for In Vitro Cell Imaging and Solid State Lighting

Abstract

We report the synthesis, systematic crystal structure, and upconversion (UC) emission in bulk and nanomaterials of NaLa(WO4)2: Yb3+/Er3+. The disordered NaLa(WO4)2 matrix has been considered as the UC host and host lattice dynamics were investigated using DFT, and neutron diffraction studies. The presence of phonons at the cut‐off frequency of ∼912 cm−1 is revealed by DFT analysis which is further confirmed by room temperature Raman studies. The optimized concentration of NaLa0.865Er0.035Yb0.1(WO4)2 is referred to as UCB and UCN with respect to particle size derived from a facile solvothermal method. Interestingly, high‐resolution microscopy studies uncovered the existence of high‐density edge dislocations in UCN nanomaterials leading to enhanced phonon scattering. Both UCB and UCN materials have shown pump power‐dependent intense UC green emission upon 980 nm laser irradiation. In addition, we have also demonstrated an excellent non‐toxicity of UCB and UCN towards Escherichia coli, Staphylococcus aureus, Candida albicans, and mammalian HeLa cell lines followed by the potential use of nanomaterials for in vitro cell imaging. Thus, the combined neutron diffraction, DFT, microscopy, and spectroscopic analysis collectively resulted in the right structure‐property relationship in these biocompatible UC green fluorescent bifunctional NaLa(WO4)2 materials.