Visible quantum cutting in green-emitting BaF2: Gd3+, Tb3+ phosphor: An approach toward mercury-free lamps

Visible quantum cutting (QC) has been observed in green emitting BaF2 co-doped with Gd3+, Tb3+ phosphor via down-conversion (DC) synthesized by wet chemical method. Powder X-ray diffraction (XRD) analysis shows structural purity of synthesized phosphors. The excitation (PLE) and PL spectra in the vacuum ultraviolet (VUV) or UV region were measured with the help of 4B8-VUV spectroscopy experimental station of the Beijing Synchrotron Radiation Facility (BSRF). In the QC process, one VUV-UV photon absorbed is cut into more than one visible photons emitted by Tb3+ through cross relaxation (CR) and direct energy transfer (DET) between Tb3+ and Tb3+ or Tb3+ and Gd3+, depending on the excitation wavelength. From the emission spectra monitored at different wavelength excitation, the two-step energy transfer process is investigated and theoretically calculated quantum efficiency observed 148% and 177% at the excitation wavelength of 174 nm and 219 nm respectively.