| Upconversion nanoparticles emit visible light when excited by near infrared radiation, making them suitable for many applications such as bioimaging, three-dimensional displays, solid-state lasers, etc. In this work, freestanding thin films, which can be fabricated by combining layer-by-layer (LbL) assembly and a sacrificial method, will be utilized to incorporate upconversion Yb 3+, Er3+ doped NaYF4 nanoparticles into multilayer thin films. LbL is a versatile method to prepare nanoscale multilayer thin films by alternately depositing positive and negative charged functional building blocks onto solid substrates. These lanthanide doped NaYF4 upconversion nanoparticles are capped with oleic acid and can be converted from hydrophobic to hydrophilic particles by extraction into a citric acid solution. The surface modified upconversion nanoparticles are uniformly deposited in the LbL thin films. A variety of techniques, e.g. atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-VIS spectroscopy, etc. was used for characterization of the nanocomposite multilayer thin films. |
