Conversion and quantum efficiency from ultraviolet light to near infrared emission in Yb³⁺-doped pyrovanadates MZnV₂O₇ (M = Ca, Sr, Ba)

Yb³⁺-doped CaZnV₂O₇, SrZnV₂O₇ and BaZnV₂O₇ were synthesized via the solid-state reaction. The polycrystalline samples were investigated by XRD and SEM measurements. The reflectance spectra, photoluminescence (PL) excitation and emission spectra, the absolute quantum efficiency (QE) of the IR emission (900-1100 nm) were measured. The efficient conversion from ultraviolet (UV) light to near-infrared (NIR) emission has been demonstrated in the Yb³⁺-doped pyrovanadates by the broadband down conversion from VO₄^3- to Yb³⁺ ions. Under UV light excitation, an intense NIR emission around 1000 nm ascribed to the ²F_5/2 → ²F_7/2 transition of Yb³⁺ ions has been observed, which just corresponds to the spectral response of Si solar cells. The NIR emission efficiency is observed to depend on the lattice of pyrovanadate. The mechanism of the NIR emission ascribed to energy transfer is discussed by taking into account the experimental results and the crystal structures.