Core–shell structured NaYF4:Yb,Tm@CdS composite for enhanced photocatalytic properties

Abstract

NaYF₄:Yb,Tm upconversion nanocrystals with hexagonal structure possess excellent photoluminescence emission characteristics. Under near infrared (NIR) light irradiation, the Yb³⁺ ions act as sensitizers to absorb the NIR light and transform NIR light into ultraviolet (UV) and visible (Vis) light continuously. Hybrid NIR-activated photocatalysts can be fabricated by combining upconversion nanocrystals with various semiconductor nanocrystals. In this paper, NaYF₄:Yb,Tm micro-rods were hydrothermally synthesized with oleic acid as capping ligand. The NaYF₄:Yb,Tm@CdS composite was fabricated by in situ generation of CdS nanoclusters on the surface of NaYF₄:Yb,Tm micro-rods. The morphologies and structures of NaY₄:Yb,Tm and NaYF₄:Yb,Tm@CdS were characterized by XRD, SEM, TEM, XPS, UV-Vis and PL spectroscopy. The results of photocatalytic experiments indicated that the NaYF₄:Yb,Tm@CdS composite displayed photocatalytic activity under NIR irradiation. In comparison with pure CdS, the photocatalytic ability of NaYF₄:Yb,Tm@CdS composite under Vis-NIR irradiation was obviously enhanced. 82% of RhB was degraded by NaYF₄:Yb,Tm@CdS catalyst within 75 min under Vis-NIR irradiation, which was more effective than pure CdS (65% degradation of RhB).