Flexible composite film with enhanced upconversion emission for ultrasensitive gas detection

Lanthanide-doped upconversion nanoparticles (UCNPs) were found promising in photovoltaic devices and nanoscale sensing due to their excellent optical properties. However, the low quantum yields severely limit their practical applications. In this work, we reported the enhanced upconversion emission by near-field modulation on all dielectric interfaces. The flexible polystyrene (PS) sphere array @UCNPs composite was fabricated by selfassembly and the NIR excitation can be highly localized and amplified in the array with proper sphere size, thus promoting the upconversion process. Based on this efficient upconversion composite film, the sensing performance on acetic acid gas were discussed in detail. The good linear relationship between the upconversion luminescence intensity and acetic acid concentration can be achieved with a detection limit of 5.2 ppm at room temperature, which is comparable with the best level reported so far. In addition, such optical signal-based sensors possessed other unique advantages such as easy fabrication, high sensitivity, long-term stability, reusability and flexibility. And the fluorescence signal enhancement factor showed less dependence on the excitation power and can emit effectively at low pump power. This all dielectric fluorescent composite with high efficiency and sensing performance can be helpful in biosensor and flexible security label applications.