Ten-fold enhancement of ZnO thin film ultraviolet-luminescence by dielectric microsphere arrays.

Here we report strong enhancement in ultraviolet-photoluminescence (UV-PL) of ZnO thin films (grown on a SiC substrate) covered by monolayer dielectric fused silica or polystyrene microspheres with diameters ranging from 0.5 to 7.5 μm. The excited light scatted in the film is collected by the microspheres to stimulate whispering gallery modes, by which the internal quantum efficiency of spontaneous emission is enhanced. Meanwhile, the microsphere monolayer efficiently couples emitted light energy from the luminescent film to the far-field for PL detection. A UV-PL enhancement up to 10-fold via a 5-µm-diameter microsphere monolayer is experimentally demonstrated in this work. The unique optical property of microsphere in photoluminescence (PL) enhancement makes them promising for high-sensitivity PL measurements as well as design of photoelectric devices with low loss and high efficiency.