Structural understanding of the spectral characteristics of SnO₂:Eu:Y₂O₃, using extended X-ray absorption fine structure

Abstract

SnO₂:Eu is a well-known luminescent material, emitting red and orange lines. The intensity ratio of red to orange emission, being sensitive to the deviation of Eu³⁺ ions from symmetric location, finds wide application as sensor. The luminescence intensity of such lanthanide-doped sensors is generally optimized by high temperature annealing. However, for the present system (SnO₂:Eu) it had been found that the red emission suddenly disappears while annealing beyond 900°C, which can however be recovered by dispersing the system in a secondary host matrix of Y₂O₃. Understanding the mechanism of this recovery has important implication for designing of phosphor. In this work, we structurally explain this spectral evolution, by employing X-ray absorption fine structure technique. The initial disappearance of the red line is realized to be due to the formation of Eu₂Sn₂O₇ and the recovery, to the intercalation of the Eu³⁺ ions from the SnO₂ surface into Y₂O₃. Oxygen vacancy in Y₂O₃ creates the asymmetric environment required for red line emission. The design implications of these findings are discussed.