Discovering new colors of luminescence in rare-earths doped CaTiO3 through co-doping

Abstract

The luminescence of CaTiO3:Pr3+ has been known since mid-90s [1] and its persistent luminescence has been explained via InterValence Charge Transfer transitions [2]. However, the trivalent dysprosium doped materials besides presenting white luminescence does not present any persistent luminescence. On the other hand, the expected red emission on materials doped with Eu3+ only occur when exciting in the forbidden 4f6-4f6 transitions. The objectives of this work are to show the synthesis and luminescence properties of CaTiO3:Dy3+ and CaTiO3:Dy3+,R3+ prepared with the sol-gel method [3, 4]. The excitation spectra of single Eu3+ or Dy3+ doped materials (Fig. left) show for Eu3+, only the 4f6-4f6 transitions while for Dy3+ both the 4f9-4f9 transitions as well as the O2-→TiIV charge transfer and the host absorption. The excitation spectrum for the Dy3+,Eu3+ co-doped material monitoring the Eu3+ emission at 610 nm exhibit both the Eu3+ intraconfigurational transitions as well as the O2-→TiIV charge transfer and the host absorption. This result indicates that there is no direct energy transfer from Dy3+ to Eu3+, but Dy3+ acts as a sensitizer for Eu3+ to be excited by host transitions. Based on experimental data the energy level diagram was constructed (Fig. right) showing that Eu3+ is deep inside the valence band.