Indium tin oxide (ITO) nanoparticles were coupled with NaYF4:(Gd, Si) using a TiO₂-solution impregnation method. Scanning electron microscopy confirmed that TiO₂ and ITO nanoparticles were loaded on the surface of the NaYF4:(Gd, Si) upconversion phosphor. The ultraviolet/visible spectra of the 20 wt.% ITO-NaYF4:(Gd, Si)/TiO₂ composites were extended at the absorption edges towards the UV-visible region. The 20 wt.% ITO-coupled NaYF4:(Gd, Si)/TiO₂ composites exhibited superior photocatalytic efficiency compared to only NaYF4:(Gd, Si)/TiO₂ under near-infrared (NIR) irradiation. Multi-wavelength NIR photons of γ > 760 nm from a Xe solar simulator source induced photo-activation through the NaYF4:(Gd, Si) activator centers. The three-cycle photocatalytic reusability performance of the 20 wt.% ITO-impregnated NaYF4:(Gd, Si)/TiO₂ composite was positively enhanced by up to 20% more than that of NaYF4:(Gd, Si)/TiO₂.