Calcination‐ and Etching‐Free Photolithography of Inorganic Phosphor Films Consisting of Rare Earth Ion Doped Nanoparticles on Plastic Sheets

It is demonstrated that patterned inorganic phosphor films consisting of rare earth ion doped nanoparticles (RE‐NPs) can be fabricated on plastic sheets using calcination‐ and etching‐free photolithography. Green up‐conversion luminescence and near‐infrared (NIR) fluorescence appears from the RE‐NPs that are prepared from Y₂O₃ doped with 1 mol% Er³⁺ and 0.85 mol% Yb³⁺. The diameter of the RE‐NPs is estimated to be about 300 nm using dynamic light scattering. Visible transmittance of the RE‐NP film fabricated by dip‐coating is more than 90%. Patterned RE‐NP films are obtained by dip‐coating the RE‐NPs on patterned photoresist films fabricated by UV exposure through a photomask, followed by selective removal of the photoresist. Optical, fluorescence, scanning electron, atomic force, and Kelvin probe force microscopies are used for the characterization of the patterned RE‐NP films. The present methodology enables fabrication of patterned RE‐NP films, not only on inorganic substrates but also on plastic sheets, with low cost and material consumption.