Elaborate Size-tuning of Silica Aerogel Building Blocks Enables Laser-driven Lighting.

Aerogels, a fascinating three-dimensional (3D) network structure composed of nano-scale building blocks as well as plenty of air in between these building blocks, have been applied in many emerging fields such as optics, energy, environment, aerospace, etc., yet a severe challenge remains in size-tuning of aerogel building blocks for particular optical applications (e.g., illumination). In this work, silica aerogels with accurate building block control were realized by adjusting surfactant concentration during synthetic process. The resulting silica aerogel monolith with spheric building blocks of ca. 24 - 40 nm, together with a deliberately created hole along the incident light direction, shows an incredibly promising application in monochromatic laser-driven lighting. The resulting coefficient of illuminance variation (CIV) is as low as 8.1%, significantly outperforms commercially available ground glass diffuser (139.0%) and polymer diffuser (249.1%), the speckle contrast is lower, as well as better, than that can be recognized by the human eye (4%), and the illuminance uniformity in the range of 0.770-0.862 is much better (higher) than that indoor workplace lighting required by the International Organization for Standardization (ISO). The lighting with any colors in the visible spectrum including white could be obtained by using three primary color lasers (450, 532, and 638 nm) with different powers simultaneously as the light source. The resulting silica aerogel with excellent thermal stability, high laser damage threshold, outstanding mechanical performance and super-hydrophobicity can be further applied to long-distance and non-contact laser-driven lighting in rain or under the water without any additional encapsulation components. Such laser-driven lighting was enabled for the first time by using silica aerogel as the diffuser, which not only broadens the application of various aerogel, but also promote lasers as a new generation of light sources. This article is protected by copyright. All rights reserved.