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UV excitation for several Eu 2þ -doped melilite crystals, Eu 2þ :Ca 2 Al 2 SiO 7 (CASM), Eu 2þ :CaSrAl 2 SiO 7 (CSASM), and Eu 2þ :Sr 2 Al 2 SiO 7 (SASM) produces long-lasting phosphorescence (1-10 2 s) from Eu 2þ ions besides the intrinsic Eu 2þ luminescence. The distribution of the radiative decay rates is due to the recombination of distant pairs of trapped electrons and holes in the crystals. The intensities of the phosphorescence for these crystals were measured as functions of temperature and time. The most intense phosphorescence was obtained from the Eu 2þ : SASM crystal. The decay curves measured for Eu 2þ :SASM below 400 K fit t Àn (n 1). This fact shows that the recombination of the distant pairs occurs through tunneling below 400 K. The temperature dependence of the intensities integrated in a time domain obeys the Arrhenius's equation with two thermal activation energies including radiative and non-radiative processes. These results suggest that holes and electrons recombine radiatively at Eu 2þ sites in the SASM crystal through thermal hopping and tunneling. On the other hand, Eu 2þ :CASM and Eu 2þ :CSASM show different behavior on the decay curves at low temperatures, satisfying t Àn (n > 1). This discrepancy may be removed by several electron and=or hole centers with different trapping energy levels.

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