Enhanced Singlet Oxygen Generation via Near‐Infrared Photo‐Activated Upconversion: Application to Amyloid Fibril Degradation

Abstract In this study, we attempted to improve the quantum yield of upconversion nanoparticles to achieve high efficiency of amyloid fibril decomposition cascade induced by near‐infrared‐active upconversion nanoparticles complexed with photosensitizers. The effects of the solvothermal reaction time on the crystalline phase of polyethylenimine‐coated NaYF 4 : Yb 3+ /Er 3+ were studied, while maintaining constant reaction temperature and concentration of the dopants Yb 3+ and Er 3+ . We found that an increased reaction time resulted in the conversion of the crystalline phase from the cubic α‐ to hexagonal β‐forms with a higher upconversion quantum yield. In addition, the prolonged reaction time effectively increased the ratio of green ( 2 H 11/2 and 4 S 3/2 → 4 I 15/2 ) to red ( 4 F 9/2 → 4 I 15/2 ) emissions, increasing the 1 O 2 generation via photosensitization to approximately 10 times that of conventional ones. Consequently, the efficiency of the amyloid fibril decomposition cascade induced by upconversion nanoparticles complexed with photosensitizers was improved.