Rare-earth activated SnO2 photoluminescent thin films on flexible glass: Synthesis, deposition and characterization

Flexible photonics is undoubtedly the next technological platform, capable to revolutionize current light-based technologies, thanks to their spatial freedom characteristics. Beyond polymer-based flexible photonics, the recent advent of ultrathin glasses with their mechanical flexibility has opened a new avenue for developing all-inorganic flexible photonic structures and devices. However, deposition and processing of functional coatings on such very thin glasses is an emerging challenge, in particular to obtain very good adhesion. Furthermore, to find proper management for maintaining the mechanical flexibility, investigation of impacts induced by processing and application of coatings on the ultrathin glasses is necessary. This work reports progress in obtaining rare-earth activated SnO2 photoluminescent thin films (SnO2:RE3+ with RE3+: Er3+ or Yb3+) on ultrathin AS 87 eco Schott glass (175 μm), valuable for development of flexible inorganic systems with efficient RE3+ luminescence. In such flexible photoluminescent thin films, SnO2 nanocrystals act as effective rare earth host-sensitizers, enhancing near-infrared emission of Er3+ or Yb3+. A sol-gel derived synthesis and fabrication protocol of SnO2:RE3+ coatings on the ultrathin glass was realized. A heat-treatment process at 500 °C for 4 h was defined to be suitable for obtaining crystallization of the coatings while avoiding thermally induced cracking of the AS 87 eco glass. The obtained SnO2:RE3+ thin films exhibit a wide transparency window with a transmittance of about 80% covering the 400 nm–3200 nm range. Three point bending test was carried out on the ultrathin glass and coated samples. Both thermal treatment and application of SnO2:RE3+ coatings connected with the thermal treatment (used for coating fabrication), resulted in a decrease of possible maximum elastic deformation of the final flexible structures.