Enhancement of NIR-triggered photocatalytic activity of Ln3+-doped NaYF4@SiO2/Ag@TiO2 nanospheres through synergistic upconversion and plasmonic effect

The multishell-structured NaYF4:Yb,Tm,[email protected]4:Yb,[email protected]2/[email protected]2 ([email protected]2/[email protected]2) nanospheres were prepared for the first time, which possessed the enhanced NIR-triggered photocatalytic activity under the synergistic effect of upconversion and plasmons. The design of [email protected] structure for NaYF4:Yb,Tm,[email protected]4:Yb,Nd upconversion nanophosphors (Yb/Tm/[email protected]/Nd UCNPs) significantly improved their upconversion luminescence (UCL) efficiency, which was increased by 12 times after coating a Yb/Nd shell on Yb/Tm/Nd seed crystals via epitaxial growth. After introduction of Ag nanoparticles, the UCL intensity of the obtained [email protected]2/Ag was further enhanced by 3.3 times compared with the bare UCNPs because the plasmon resonance frequency of Ag overlapped with the visible emission peaks of UCNPs, which permitted an effective surface plasmon-coupled emission, resulting in the increase of emission intensity for UCNPs. Therefore, the final [email protected]2/[email protected]2 could absorb the plasmon-enhanced NIR-to-UV/Vis lights from UCNPs to obtain its photocatalytic activity. Significantly, the photodegradation of Rhodamine B under the action of [email protected]2/[email protected]2 was 26.9 % higher than that under the action of [email protected]2@TiO2. [email protected]2/[email protected]2 also exhibited a better photocatalytic antibacterial activity against B. subtilis than [email protected]2@TiO2. In the presence of [email protected]2/[email protected]2, bacteria were completely killed after 15 min of 808 nm NIR illumination. Finally, the possible photocatalytic mechanism of [email protected]2/[email protected]2 was discussed based on the results of scavenger test.