Enhanced energy transfer from Bi3+ to Eu3+ ions relying on the criss-cross cluster structure in MgMoO4 phosphor

The discovery of efficient red-emitting-phosphor materials is critical to the next-generation white light-emitting diodes (white LEDs). In this work, we prepared a promising red-phosphor candidate: MgMoO4:Eu3+,Bi3+,M (M=Li+, Na+, K+) with a standard solid-state reaction method. This material had high luminescence intensity upon ultraviolet light (UV), near ultraviolet light (near-UV), and blue excitation. We discovered that every four Mg sites formed a criss-cross unit site in the MgMoO4 structure. These sites were used to remotely control the relative distance between Bi3+ and Eu3+ ions through changing the doping concentrations and charge compensation. A distinct new excitation band from the MgMoO4:Eu3+,Bi3+,M (M=Li+, Na+, K+) phosphors coming from the 1S0→3P1 transition of Bi3+ ions was clearly observed at about 352nm. Moreover, the super energy transfer coming from Bi3+ to Eu3+ ions was designed and realized. Bi3+ and Eu3+ begin to sit in two adjacent Mg(1) sites when their total molar concentration is beyond 1/4. Thus, the new super energy-transfer emerges due to the adjacent Bi3+ and Eu3+ ions. The process and mechanism of the super energy transfer were further discussed. Our results indicated potential industrial applications of MgMoO4:Eu3+,Bi3+,M in white LEDs.