Structure, Long Persistent Luminescent Properties and Mechanism of a Novel Efficient Red Emitting Ca2Ga2GeO7:Pr3+Phosphor.

Abstract A novel red emitting long persistent luminescent phosphor Ca 2 Ga 2 GeO 7 :Pr 3+ (2217) was developed by solid state method at 1300 °C in air. The refined crystal structure of Ca 2 Ga 2 GeO 7 host was solved. The intense red long persistent luminescence originates from the f - f transitions of Pr 3+ centers at highly disordered Ca 2+ sites in CaO 8 polyhedrons. It can be properly recorded for 1.5 h by the definition of 0.32 mcd/m 2 and is actually visible for more than 5 h by dark-adapted vision in darkness. At least one type of intrinsic lattice defects of the Ca 2 Ga 2 GeO 7 host as proper shallow traps exists in Ca 2 Ga 2 GeO 7 :Pr 3+ material and the depth of the traps is calculated to be 0.59 eV, which is very suitable for long persistent luminescence. It reveals that the Pr 3+ dopants not only act as emitters but also increase the density of these significant intrinsic traps, resulting in the efficient persistent luminescence of Pr 3+ . The retrapping and tunneling effects are demonstrated to be responsible for the nonexponential and much slower decay behaviors in the late slow-decay stage ( t  > 300 s). A new parameter of threshold depth is firstly defined for the evaluation of the retrapping and tunneling effects and it is calculated to be 0.76 eV in this case by a classic multi-peak fitting method based on general-order kinetics. Finally, the long persistent luminescence mechanism of this Ca 2 Ga 2 GeO 7 :Pr 3+ phosphor is proposed according to these investigation results.