Stable Inks Containing Upconverting Nanoparticles Based on an Oil-in-Water Nanoemulsion.

An oil-in-water nanoemulsion capable of dispersing upconverting nanoparticles (UCNPs) for 7 months was investigated. Negative staining transmission electron microscopy shows that the UCNPs reside in the oil phase of the nanoemulsion. Dynamic light scattering measurements indicate that the majority of the oil volume is contained in droplets less than 1 μm in diameter. The system studied could be used to inkjet print UCNPs at least 7 months after the ink was first formulated. Nanoemulsion stability was tested in the short term, over 11 days, using an ink stability test developed for this research. It was found that after an initial loss of UCNPs, the majority of the UCNPs remained well-dispersed in solution. The UCNP dispersion was stable for longer periods under storage at 333 K compared to storage at 277 K.