Citrobacter sp. R1, a highly efficient algicidal bacterium, undergoes a serious degeneration after long-term preservation. Here, we prepared a Li-doped up-conversion material ([Y2SiO5; Li (1%)]) to recover the degenerated Strain R1. As a result, the [Y2SiO5; Li (1%)] successfully enhanced the maximum algicidal activity of Strain R1 from 43.2 +/- 1.2 to 72.5 +/- 1.3%. In terms of recovery mechanisms, 1) the [Y2SiO5; Li (1%)] could convert visible light into UVC and UVA with unusual wavelengths, creating conditions for inducing reverse mutation in Strain R1, affecting the metabolism of Strain R1 and then recovering the bacterium; 2) the [Y2SiO5; Li (1%)] did not only enhance the secretion of 3-hydroxypropionic acid, the algicidal compoundwhich Strain R1 continues to produce even after degeneration, but also it recovered the ability of Strain R1 to secrete three new algicidal compounds. This study provides a new idea of employing up-conversion material [Y2SiO5; Li (1%)] in microbial degeneration recovery. (C) 2020 Elsevier B.V. All rights reserved.