Enhanced visible/NIR driven catalytic activity in presence of neodymium (Nd³⁺), for Yb³⁺ and Tm³⁺ doped NaYF₄ nanoparticles

Removal of organic dye-based impurities from water has been achieved traditionally by the use of photocatalysts. ZnO is a commonly used photocatalyst that works when irradiated by UV irradiation. Since the UV fraction in a solar spectrum is very small, there is a scope of utilizing the near-infrared and visible spectrum for the process of dye degradation. We synthesized a novel tri-dopant upconversion nanoparticle (NaYF₄:Yb,Tm,Nd) system using a simplified microwave-assisted technique and combined it with ZnO particles for methylene blue dye degradation studies. We examined the role of neodymium (Nd³⁺⁾ dopant on the efficiency of dye degradation when illuminated under an inexpensive tungsten halogen lamp source. X-ray diffraction studies revealed that the presence of Nd³⁺ in the crystal lattice leads to a reduction in the particle size due to shrinkage in the crystallite size. The presence of Nd³⁺ in upconversion nanoparticles revealed several characteristic absorption bands from 520 nm to 870 nm along with the characteristic 980 nm corresponding to (ytterbium) Yb³⁺. The power-dependent study at 980 nm confirmed the multi-photon process of upconversion. The degradation efficiency revealed up to 92% degradation for 5 mg L⁻¹ of dye. The degradation efficiency of upconversion nanoparticles and ZnO system in the presence of Nd³⁺ was 72% and in the absence of Nd³⁺ was 58%, for a dye concentration of 10 mg L⁻¹. The dye degradation rate constant was higher for NaYF₄:Yb,Tm,Nd and ZnO system (0.0041 min⁻¹) compared to NaYF₄:Yb,Tm, and ZnO set (0.0029 min⁻¹). Thus, the presence of Nd³⁺ widens the absorption spectra of UCNP in both the visible and near-infrared (NIR) range.