Luminescence excitation study of the higher energy states of Pr3+ and Mn2+ in SrAlF5, CaAlF5, and NaMgF3

Abstract

The possibility to use Mn2+ co-doping to modify the emission properties of Pr3+-based quantum cutting phosphors—i.e., phosphors that emit one UV and one visible photon for each absorbed vacuum UV (VUV) photon—into phosphors that emit two visible photons, was studied experimentally. In this respect a luminescence excitation study, using synchrotron radiation, between 500 and 50 nm of Pr3+ and Mn2+ impurities in SrAlF5, CaAlF5, and NaMgF3 was performed. Excitation of Pr3+ into the 4f5d excited states results in emission of UV photons from the S01 state followed by visible photons from the P03 state with an internal quantum efficiency exceeding 100%. It was found that a favorable overlap between the S01→I61 Pr3+ emission and the A16→Eg4, A1g4 Mn2+ absorption exists that should promote energy transfer from Pr3+ to Mn2+. However no such energy transfer could be observed in SrAlF5. At higher excitation energies (>7 eV) intense structured Mn2+ excitation bands are found that are assigned to 3d5→3d44s transitions, Mn2+ related charge transfer transitions, and Mn2+ bound excitons. These bands have an unfavorable overlap with the Pr3+ 4f5d states, preventing efficient selective Pr3+ excitation, prerequisite for the quantum cutting process.