Over 1000-Fold Enhancement of the Unidirectional Photoluminescence from a Microsphere-Cavity-Array-Capped QD/PDMS Composite Film for Flexible Lighting and Displays

The development of quantum dot (QD) composite films for lighting and displays is of great importance because of their exceptional mechanical flexibility, chemical stability, and optical tunability. Generally, QDs are attached to plasmonic nanostructures to enhance their photoluminescence (PL) emission. However, plasmonic QD composite films suffer from deteriorated inherent quantum yields and lower enhancement ratios due to variations in the refractive index and dielectricity in the composites. Herein, the use of a dielectric microsphere cavity is reported to realize over 1000-fold enhancement of the PL in CdSe/ZnS QD/polydimethylsiloxane films with a highly unidirectional emission angle of approximate to 9 degrees. The field regulation by the optical whispering-gallery resonance and directional antenna effect at the microscale is revealed to interpret the PL enhancement mechanism. Additionally, the microsphere cavity allows for the enhancement of white-light emission in the RGB-QD hybrid composite film. The present work inspires a straightforward strategy for boosting the light efficiency in QD composite films, with promising applications in flexible lighting/display devices.