Near-infrared graded-index antireflection coating from ZnSe hollow nanospheres

A double-layer broadband antireflective coating (ARC) with graded-index was prepared on ZnSe substrate by using ZnSe hollow nanoparticles (HNPs). The bottom high-refractive-index layer (HIL) was made by closed-packed ZnSe HNPs array, and the top low-refractive-index layer (LIL) was gained by a sacrificial template method. The refractive indices of both layers are close to the theoretical model. A high transmittance, up to 91.5%, is achieved in the near-infrared spectral range with incident angles ranging from 0° to 30°. It also exhibits excellent mechanical stability, and sustains high transmittance over a much wider optical band, compared to the single-index ARC, making it promising for further applications.