Luminescence excitation study of the higher energy states of Pr3+ and Mn2+ in SrAF5, CaAlF5, and NaMgF3

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 S-1(0) state followed by visible photons from the P-3(0) state with an internal quantum efficiency exceeding 100%. It was found that a favorable overlap between the S-1(0)-->I-1(6) Pr3+ emission and the (6)A(1)-->E-4(g), (4)A(1g) 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 3d(5)-->3d(4)4s 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. (C) 2004 American Institute of Physics.