Pr→Mn Energy Transfer in SrB_4O_7∶Pr,Mn

The luminescence of Pr~(3+) or Mn~(2+) singly doped as well as Pr~(3+) and Mn~(2+) codoped SrB_4O_7 powder microcrystalline samples were investigated using synchrotron radiation.The photon cascade emission origi-(nating) from the ~1S_0 level was observed in the SrB_4O_7∶Pr~(3+)(0.1%,mol fraction) sample upon 206 nm excitation.There are desirable spectral overlaps in the region of 330~430 nm between the emission spectra of the SrB_4O_7∶Pr~(3+) sample and the excitation spectra of the SrB_4O_7∶Mn~(2+) sample monitoring the Mn~(2+) luminescence at 640 nm.The wavelengths corresponding to transitions ~1S_0→~1I_6,~3P_(2,1,0)(405 nm) and ~1S_0→~1D_2(340 nm) of Pr~(3+) coincide very well with those corresponding to transitions ~6A_(1g)→~4E_g-~4A_(1g)(410 nm) and ~6A_(1g)→~4T_(2g)(350 nm) of Mn~(2+),respectively.These spectral overlaps are in favor of the energy transfer from Pr~(3+) to Mn~(2+),converting the first step photon from Pr~(3+):~1S_0 in the unpractical ultraviolet or near-ultraviolet regions into the red Mn~(2+) emission.A comparison of the room temperature emission spectra of the SrB_4O_7∶Pr~(3+),Mn~(2+) sample with that of the SrB_4O_7∶Pr~(3+) sample revealed the existence of the proposed energy transfer between Pr~(3+) and Mn~(2+).This conclusion about Pr→Mn energy transfer was also supported by the evidences from the low temperature(10 K) spectra and decay curves of 405 nm emission from Pr~(3+) singly doped and Pr~(3+),Mn~(2+) codoped samples.The efficiency of the energy transfer was estimated to be 43% by a simple equation based on the comparison of the emission spectra of the SrB_4O_7∶Pr~(3+),Mn~(2+) sample with that of the SrB_4O_7∶Pr~(3+) sample,thus a 143% quantum efficiency was achieved,suggesting an promising VUV phosphor based on Pr~(3+) and Mn~(2+) combination.