escape function

Angular redistribution of near-infrared emission from quantum dots in 3D photonic crystals
B. H. Husken, A. F. Koenderink, and W. L. Vos
J. Phys. Chem. C 117, 3431-3439 (2013)

Light exiting from real photonic band gap crystals is diffuse and strongly directional
A. F. Koenderink, and W. L. Vos
Phys. Rev. Lett. 91, 213902: 1-4 (2003)