Nonimaging Optical Gain in Luminescent Concentration through Photonic Control of Emission Étendue

ABSTRACT: Luminescent and nonimaging optical concen-tration constitute two fundamentally different ways of collecting and intensifying light. Whereas nonimaging concentrators based on reflective, refractive, or diffractive optics operate most effectively for collimated light, lumines-cent concentrators (LCs) rely on absorption, re-emission, and waveguiding to concentrate diffuse light incident from any direction. LCs have been explored in many different shapes and sizes but have so far been unable to exploit the power of nonimaging optics to further increase their concentration ratio because their emission is angularly isotropic. Here, we use a luminescent thin film bilayer to create sharply directed conical emission in an LC and derive a nonimaging optical solution to leverage this directionality for secondary geometric gain ranging up to an order of magnitude or higher. We demonstrate this concept experimentally using a custom compound parabolic optical element index-matched to the LC surface and show that it delivers three times more luminescent power to an opposing GaAs photovoltaic cell when the emission profile is conically directed than when it is isotropic or the nonimaging optic is absent. These results open up a significant and general opportunity to improve LC performance for a variety of applications including photovoltaics, photobioreactors, and scintillator-based radiation detection