Visible quantum cutting in green–emitting BaGdF 5:Tb 3+ phosphors via downconversion

Abstract

The visible quantum cutting (QC) under the excitation at 215 and 187 nm in a newly discovered BaGdF 5:Tb 3+ via downconversion mechanism has been observed and investigated. We have measured the vacuum ultraviolet (VUV) excitation and emission spectra and proposed possible mechanisms to rationalize the observed QC effect. In QC process, one short-wavelength UV or one VUV photon absorbed by Tb 3+ was found to split into more than one visible photon emitted by Tb 3+ through cross-relaxation and subsequent direct energy transfer between Tb 3+ and Tb 3+ and/or Gd 3+ ions, depending on the excitation wavelength. On the basis of the calculations from the emission spectra in the visible region obtained, we have obtained optimal quantum efficiency as high as 168% and 180% for green-emitting BaGdF 5:Tb 3+ under excitation at 215 and 187 nm, respectively.