Direct Patterning of Colloidal Quantum-Dot Thin Films for Enhanced and   Spectrally Selective Out-Coupling of Emission
  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. 
Ferry Prins, David K. Kim, Jian Cui, Eva De Leo, Kevin M. McPeak,   David J. Norris
cond-mat.mes-hall