NIR-Fluorescent Hybrid Materials of Tm³⁺ Complexes Carried by Nano-SiO₂ via Improved Sol-Gel Method

Tm³⁺ has obvious emission characteristics in the near-infrared band. Thulium ions combined with different organic ligands lead to different fluorescent properties. In the near-infrared region, Tm³⁺ is a down-conversion fluorescent material that is unstable under high temperature and acidic conditions. Moreover, in those complex environments, the fluorescence from Tm³⁺ complex is usually degraded. In this work, two kinds of near-infrared fluorescent complexes, Tm(TTA)₃phen and Tm(DBM)₃phen, were prepared, and the intensity of their fluorescence is compared. The fluorescence intensity at 802 nm is greatly improved compared with Tm(TTA)₃phen, and the intensity of the emission at 1235 nm and 1400-1500 nm is also enhanced. Moreover, the emission lifetime of SiO₂-Tm(TTA)₃phen is 50.38 μs. Tm(TTA)₃phen complex and SiO₂-Tm(TTA)₃phen hybrid materials have better fluorescence than Tm(DBM)₃phen and SiO₂-Tm(DBM)₃phen. Therefore, HTTA is a better choice of organic ligands for Tm³⁺. The NIR-fluorescent hybrid materials prepared have stronger fluorescence after combining with nano-SiO₂compared with pure Tm³⁺ complexes, and have stronger structural stability compared with pure nano-SiO₂.