Synthesis and cytotoxic effects of SrAl_2O_4 persistent luminescence nanoparticles co-doped with Eu^2+/Dy^3+ ions

Persistent luminescence strontium aluminate nanoparticles co-doped with Eu2+ and Dy3+ were prepared by urea-assisted combustion synthesis. Different percentages of co-dopants were evaluated in order to optimize luminescence of the nanophosphor. Luminescence measurements showed that excitation of this green-emitting phosphor occurred within a wide range of wavelengths (254 – 460 nm) while the half-life time of persistent luminescence laid within the seconds regime. Presence of Dy3+ as the co-dopant enhanced the green emission in this interval of time, and the entire decay time occurred in minutes. Crystallinity and morphology were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Strontium aluminate co-doped with 1%Eu, and 1%Dy, and 1%Eu, and 3%Dy emitted an intense green signal and long decay time. These crystal nanophosphors displayed sizes of 18 nm and 22 nm, respectively. The cytotoxic effect of nanoparticles was determined by a cell viability test where the tri-methyl-tetrazolium reagent (MTT) was reduced only by metabolically active cells. Different concentrations of bare nanoparticles were tested in a 96-well plate containing 10, 000 cells per well of a human cervix carcinoma cell line (HeLa). Evaluation of cell viability by this cytotoxic assay showed that in most of the cases cell viability was higher than 60% after incubation with bare nanoparticles. Since our bare nanoparticles were not cytotoxic, these results open a broad field of biomedical applications for phosphorescent materials as cell biolabels and imaging research area.