Elucidating the role of metal-ion co-doping towards boosting upconversion luminescence in gadolinium vanadate

Abstract

Metal co-doping is a popular approach for boosting two-photon upconversion (UC) luminescence in phosphors. The underlying mechanisms of this enhancement are still debated, being attributed primarily to modification of lattice parameters and enlargement of grain size among other effects. However, little effort has been made to elucidate the role and relative contribution of such phenomena. Hence, this study aims to isolate the comparative effects of these factors on UC luminescence using GdVO₄:Yb³⁺/Er³⁺ phosphors as a model system. The nanoscale phosphors – co-doped with Zn²⁺ (5–30%) or Sc³⁺ (5–25%) – were prepared using a co-precipitation method. Zn²⁺ co-doping resulted in a photoluminescent quantum yield (PLQY) boost of ∼60 × under 980 nm excitation (15 W cm⁻²). This improvement was attributed largely to the simultaneous action of lattice shrinkage and particle size enlargement. Only ∼20 × enhancement was achieved via Sc³⁺ co-doping, attributed exclusively to reduction in the lattice. The results indicate that particle size is likely the largest contributor towards improved UC in inorganic phosphors. This trend was also confirmed through (Sc³⁺/Zn²⁺-free) larger microparticles–synthesized via a solid-oxide method – that exhibited ∼50 × improvement.