Damselflies Overcome Color Saturation Barriers of Photonic Glasses via Structural Dispersion and Pigment Loading

Abstract

Biologys strategies for manipulating light offer rich inspiration for the design of sustainable replacements to conventional pigments in paints, coatings, and displays. For these applications, where angle-independent color is required, photonic glasses, composed of random arrangements of dielectric spheres, offer a promising solution. However, their intrinsic disorder, particularly from particle polydispersity, fundamentally limits their color saturation and practical utility. In contrast, insects like damselflies and dragonflies exhibit surprisingly vivid, non-iridescent structural colors, despite relying on disordered photonic structures. Here, we show how damselflies combine compositional and structural dispersion to overcome color saturation limits of photonic glasses. Firstly, doping transparent particles with yellow pigments dramatically enhances blue-green structural resonances by the coupled effects of narrowband absorption and refractive index (material) dispersion. Secondly, the refractive index of the nanospheres varies with their size and crystallinity. This gives rise to a structural dispersion which maintains consistent optical path lengths in polydisperse assemblies, preserving high color purity. Finally, we show how damselflies tune their structural colors during maturation by precisely modulating the size of the nanospheres. Remarkably, the tuning of particle size, refractive index and pigment loading, arises naturally during the development of the pigment cells - where the pteridine nanospheres undergo a process of densification, crystallization and metabolic maturation.