A light converting optical system employing a planar light trapping optical structure illuminated by a monochromatic light source. The light trapping optical structure includes a photoresponsive layer including semiconductor quantum dots. The photoresponsive layer is configured at a relatively low thickness and located between opposing broad-area surfaces that confine and redistribute light within the structure and cause multiple transverse propagation of unabsorbed light through the photoresponsive layer to enhance absorption. The light trapping optical structure further incorporates various microstructured surfaces including light-distributing surface relief features such as linear microlenses, prismatic surface relief features and/or linear grooves.