Investigation On Preparation And Upconversion Luminescence Of Eu/ Yb/ Tm Doped 12CaO·7Al₂O₃

Rare-earth ions doped 12 Ca O· 7Al2O3(C12A7) has been a promising new material for photo-electronic applications. In this paper, 12 Ca O· 7Al2O3 doped with Eu3+/Yb3+/Tm3+ is prepared via high temperature solid-state reaction method. The synthesis and property of upconversion are studied. In Addition, the effects of concentration and the interaction of Eu3+/Yb3+/Tm3+ are discussed to analyze the proposed upconversion emission mechanism.The series of Eu3+/Yb3+/12 Ca O· 7Al2O3 and Eu3+/Yb3+/Tm3+/12 Ca O· 7Al2O3 samples are synthesis by high temperature solid-state reaction method, and the optimal time and temperature are 6 h and 1200 ℃. The X-Ray powder diffraction, UV-Visible absorption spectrum and Raman spectrum illustrate the unchanged crystal structure of Ca O· 7Al2O3 and possibility of efficient upconversion emission when the concentration of doped ions is not high.The upconversion property of Eu3+/Yb3+/12 Ca O· 7Al2O3 is studied and the upconversion emissions are found at green, red and near-infrared range, including 504 nm(5D2â†'7F3), 548 nm(5D1â†'7F1), 578 nm(5D0â†'7F0), 588 nm(5D0â†'7F1), 616 nm(5D0â†'7F2), 651 nm(5D0â†'7F3), 704 nm(5D0â†'7F4) and 856 nm(5D0â†'7F6). The effects of Yb3+ ions on both intensity and chromaticity of upconversion emissions follow a concentration-dependent manner. The pump power dependence of upconversion emissions indicates the fact that it is a cooperative sensitized upconversion, and then the mechanism is analyzed.The upconversion property of Eu3+/Yb3+/Tm3+/12 Ca O· 7Al2O3 is studied, and emissions of Eu3+ ions are enhanced by doping Tm3+ ions. This effect becomes distinct while the concentration of Tm3+ ions is high, which indicates the energy transfer from Tm3+ to Eu3+. In return, the intensity of Tm3+ ions emissions becomes lower. Combined with the energy structure of doped ions and pump power dependence of upconversion, the energy transfer is analyzed, including ET1: 7F0(Eu3+) + 1G4(Tm3+) â†'5D2(Eu3+) + 3H6(Tm3+), ET2: 7F0(Eu3+) + 1D2(Tm3+) â†'5D2(Eu3+) + 3H5(Tm3+), in which Tm3+ ions absorb energy from Yb3+ ions and transfer to Eu3+ ions. It is concluded that the energy transfer is exist, and Tm3+ ions play a bridging role. Therefore, Eu3+ ions can realize more efficient upconversion emissions through the route of Yb3+â†'Eu3+ and Yb3+â†'Tm3+â†'Eu3+ by doping Tm3+ ions.