Visible quantum cutting in green–emitting BaGdF5:Tb3+ phosphors via downconversion

The visible quantum cutting (QC) under the excitation at 215 and 187 nm in a newly discovered BaGdF5:Tb3+ 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 Tb3+ was found to split into more than one visible photon emitted by Tb3+ through cross-relaxation and subsequent direct energy transfer between Tb3+ and Tb3+ and/or Gd3+ 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 BaGdF5:Tb3+ under excitation at 215 and 187 nm, respectively.