Photoluminescence properties and energy transfer of red phosphors Y2P4O13: Gd3+, Eu3+

The energy transfer diagram of Y2P4O13: Gd3+,Eu3+ phosphor is demonstrated by five main energy transfer processes. Under excitation at VUV light (140 nm), the electrons can transfer from an oxygen 2p orbital to an empty 4f orbital of Gd3+ (O2-→Gd3+ absorption), reaching the excited state of O-Gd CTB. Then the electrons will move to the excited state of host by nonradiative relaxation (Ⅰ). Some electrons will jump to the excited level 6GJ nearest Gd3+ ions (Ⅱ) by the phonon-aided non-radiative relaxation; after relaxing to state 6PJ, Gd3+ ions will be transited to 8S7/2 with corresponding emission (311 nm). Some other electrons will jump to the excited state of O-Eu CTB (Ⅲ). After relaxing to the excited state 5H5, 5D2, 5D1, and 5D0 (Ⅳ) of Eu3+, the transitions from the 5DJ (J = 0, 1, 2) to ground state 7F0, resulting in the characteristic emission of Eu3+. Moreover, the energy of 6PJ of Gd3+ is slightly higher than the Eu3+ 5DJ levels, which is possiblely due to the phonon-aided non-radiative relaxation from 6PJ level of Gd3+ to the 5DJ level of Eu3+(Ⅴ) and produces characteristic emissions of Eu3+. Under excitation at 162 nm, the electrons will jump from ground state to excited state of host (host absorption); then the four main energy transfer processes will occur (II~V).173