Synthesis, optical properties and toxic potentiality of photoluminescent lanthanum oxide nanospheres

Spherical, luminescent La2O3:RE(RE = Pr and Eu) nanospheres (NSs) having an average grain size of 90-130 nm were prepared by homogeneous urea-based decomposition. Their toxic potentiality was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and neutral red uptake (NRU) assays. X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis, Brunauer-Emmett-Teller surface area analysis, Fourier-transform infrared spectroscopy, FT-Raman spectroscopy, and photoluminescence spectroscopy were conducted to characterize the chemical composition, crystallinity, morphology, surface chemistry, texture, optical properties, and luminescent properties of the prepared materials. SEM and TEM micrographs clearly revealed a spherical crystalline structure with a smooth surface and narrow size distribution. The emission spectrum of La2O3:Eu NSs revealed a dominant magnetic-dipole (D-5(0)-> F-7(1)) transition at 589 nm and an electric-dipole (D-5(0)-> F-7(2)) transition at 614 nm; NSs produced a strong orange-red color when irradiated with UV light. The remarkable luminescence efficiencies of these emission transitions suggested that the nanophosphor is highly crystalline. MTT and NRU assays were conducted to evaluate the concentration-dependent toxicity of NSs on MCF-7 and A-549 cell lines. Both assays indicated that cell viability decreases with increasing NS doses, owing to increased exposure to the metal oxide surface and increased crystalline size. Good cell viability was observed at low concentrations, but toxicity increased at higher NS doses. Because of their excellent luminescent and optical features, the as-prepared nanomaterials have potential applications in laser-based biological events.