Direct identification of energy transfer mechanism in CeIII-MnII system by constructing molecular heteronuclear complexes

Sensitization of metal-centered forbidden transitions is of great significance. Solid MnII-based phosphors with d-d forbidden transition sensitized by CeIII with d-f allowed transition are promising light conversion materials, but the energy transfer mechanism in CeIII-MnII is still in dispute for the uncertainty of distances between metal centers. Herein, for the first time, we explored the energy transfer mechanism in two well-designed luminescent heteronuclear complexes with clear crystal structures, i.e. Ce-N8-Mn and Ce-N2O6-Mn (N8 = 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane; N2O6 = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane). Short distances between metal centers facilitate efficient energy transfer from CeIII to MnII in both complexes, resulting in high photoluminescence quantum yield up to unity. After systematic study of the two heteronuclear complexes as well as two reference complexes Ce(N8)Br3 and Ce(N2O6)Br3, we concluded that dipole-quadrupole interaction is the dominant energy transfer mechanism in the heteronuclear complexes.