A lignin-enrichment approach for processing natural wood into highly NIR-selective optical filters

Transparent wood engineering enables the transformation of natural wood into various optical materials. However, typical top-down strategies rely on lignin removal, which significantly reduces the near-infrared (NIR) selectivity of the resulting materials, making it challenging to develop wood-based NIR optical filters. Herein, we present a lignin-enrichment approach to fabricate highly NIR-selective optical filters directly from natural wood. By enriching the lignin content from 19.81% to 35.19%, we amplify its dual functionality in ultraviolet-visible (UV-Vis) light absorption and binding ability, increasing the NIR selectivity of wood after densification. The resulting wooden filters completely block light below 600 nm while achieving an NIR transmittance exceeding 80%, enabling them to harness 77.90% of solar NIR for phototherapy. This lignin-enrichment approach not only establishes a transformative strategy for designing NIR optical filters but also promotes the efficient utilization of natural wood and solar NIR energy.