Calcination-free liftoff photolithography of mixed dip-coated films consisting of rare-Earth-ion-doped nanoparticles on plastic sheets.

We discuss the calcination-free liftoff photolithography of inorganic phosphor films consisting of two kinds of rare-earth-ion-doped (RE) nanoparticles dip-coated onto plastic sheets. Green and red upconversion luminescence were emitted from the RE-nanoparticles prepared from Y2O3 nanoparticles doped with 1 mol% Er3+ and 0.75 mol% Yb3+ (RE-1-nanoparticles) and those doped with 3 mol% Er3+ and 7 mol% Yb3+ (RE-2-nanoparticles), respectively. Near-infrared (NIR) fluorescence was also observed in the RE-1- and RE-2-nanoparticles. The visible transmittance of the RE-nanoparticle films was more than 90%. The intensity ratio of the green to red upconversion luminescence was controlled by adjusting the mixing ratio of the RE-1- and RE-2-nanoparticles. These results indicate that the multicolor-emitting devices can be fabricated easily for applications of flexible inorganic phosphor films to displays, emitting devices, and sensors with long operating lifetimes and resistance to UV light, air, and water.