  We report on a template-stripping method for the direct surface patterning of
colloidal quantum-dot thin films to produce highly luminescent structures with
feature sizes less than 100 nm. Through the careful design of high quality
bulls-eye gratings we can produce strong directional beaming (10{\deg}
divergence) with up to six-fold out-coupling enhancement of spontaneous
emission in the surface-normal direction. A transition to narrow single-mode
lasing is observed in these same structures at thresholds as low as 120
{\mu}J/cm2. Furthermore, making use of the size-tunable character of colloidal
quantum dots, we demonstrate spectrally selective out-coupling of light from
mixed quantum-dot films. Our results provide a straightforward route towards
significantly improved optical properties of colloidal quantum-dot assemblies.

Mesoscale and Nanoscale Physics