Upconversion Nanoparticle/Siloxane Hybrid Composite with Highly Stable Photoluminescence against Heat and Moisture

Abstract

Herein, we report a siloxane-encapsulated upconversion nanoparticle (NaYF4 : Yb, Er or Tm) hybrid composite (SE-UCNP) which exhibits excellent photoluminescence (PL) stability for over 40 days even at elevated temperature, in high humidity, and in harsh chemicals. The SE-UCNP is synthesized via UV-induced free-radical addition reaction of UCNP dispersed oligosiloxane (UCNP-Oligosiloxane) resin obtained from the in-situ sol-gel condensation reaction of silane precursors in the presence of UCNPs. The siloxane matrix with random network structure by Si-O-Si bonds successfully encapsulates the UCNPs with chemical linkages between the siloxane matrix and organic ligands on UCNPs. This encapsulation results in surface passivation retaining intrinsic fluorescent properties of UCNPs under severe conditions (e.g., 85°C, 85% relative humidity) and a wide range of pH (from 1 to 14). As an application example, we fabricate a two-color binary micro-barcode based on SE-UCNP via a low-cost transfer printing process. Under near-infrared irradiation, the binarysequences in our barcode are readable enough to identify objects using a mobile phone camera. The hybridization of UCNPs with a siloxane matrix provides the capacity for highly stable UCNP-based applications in real environments