Luminescence excitation study of the higher energy states of Pr3+ and Mn2+ in SrAlF5, CaAlF5, and NaMgF3
Résumé
The possibility to use Mn21 co-doping to modify the emission properties of Pr31-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 Pr31 and Mn21 impurities in SrAlF5 , CaAlF5 , and NaMgF3 was performed. Excitation of Pr31 into the 4 f 5d excited states results in emission of UV photons from the 1S0 state followed by visible photons from the 3P0 state with an internal quantum efficiency exceeding 100%. It was found that a favorable overlap between the 1S0→1I6 Pr31 emission and the 6A1→4Eg , 4A1g Mn21 absorption exists that should promote energy transfer from Pr31 to Mn21.
However no such energy transfer could be observed in SrAlF5 . At higher excitation energies ~.7 eV! intense structured Mn21 excitation bands are found that are assigned to 3d5→3d44s transitions, Mn21 related charge transfer transitions, and Mn21 bound excitons. These bands have an unfavorable overlap with the Pr31 4 f 5d states, preventing efficient selective Pr31 excitation, prerequisite for the quantum cutting process.
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