Quenching mechanisms of the optical centers in Eu3+-doped nanophosphors under charge transfer excitation

As the size of Eu3+-doped phosphors decreases in nanoscale, the top of the valance band is elevated and the zero-phonon charge transfer (CT) energy is decreased; the rigidity of the lattice environment is decreased and the CT state (CTS) coordinate offset is enlarged. The decrease in zero-phonon CT energy and the enlargement of CTS coordinate offset mean the displacement of CTS in the configurational coordinate diagram (CCD). The CTS displacement in CCD results in the decrease in CTS feeding to the emitting D-5 states and the increase in transition probability from the CTS to the F-7 states, the excitation of the optical centers tends to be relaxed by sending phonons to the host lattice. Based on the quenching mechanisms of the optical centers progressively clarified in this paper, a feasible coating method is proposed to improve the luminescence efficiency for Eu3+-doped nanophosphors under CT excitation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3499665]