Optical processes in (Y,Bi)VO4 doped with Eu3+ or Pr3+.
Résumé
Zircon and fergusonite-type vanadates either undoped or doped with Eu3+ or Pr3+ are synthesized in the system (Y,Bi)2O3-V2O5 by solid state and coprecipitation procedures. Their optical properties are investigated at 300 and 77 K and the luminescence mechanisms are discussed on the basis of energy level schemes that combine the host and the dopant states. Fergusonite BiVO4 is shown to glow in the deep red region at 77 K upon excitation at 450 nm and shorter wavelengths. Host sensitization is demonstrated in Eu3+-doped fergusonite BiVO4 and zircon BiVO4 at 77 K, but lost as temperature is raised to 300 K. The origin of this effect is addressed by considering the nature of the host-band edge states and self-quenching processes. The near-UV excited luminescence in the system (Y, Bi)VO4:Pr3+ (zircon) consists of the yellow bandlike emission of the zircon host and of the characteristic red 1D2 → 3H4 emission lines of Pr3+ in vanadates. The relative contribution of these features can be fine-tuned at room temperature by adjusting the composition of the materials or the excitation wavelength.