Photon upconversion crystals doped bacterial cellulose composite films as recyclable photonic bioplastics

Biopolymers used as substitutes for synthetic polymers in photonics have mostly provided linear optical color responses. This work expands their use to nonlinear optics by integrating triplet–triplet annihilation photon upconversion (TTA-UC) crystals with bacterial cellulose (BC). A biomaterial is prepared by crystallizing Pd(II) meso-tetraphenyl tetrabenzoporphine (PdTPBP, sensitizer) and 9,10-diphenylanthracene (DPA, annihilator) on BC hydrogel, with gelatin coating to improve optical transparency via refractive-index matching. The composite upconverts 633 nm red light to 443 nm blue light and shows a characteristic quadratic-to-linear dependence of emission on excitation power density. At end-of-life, physical disassembly enables recovery of 66 ± 1% of the annihilator; residual biomass is biodegradable, demonstrating a sustainable photonic material.