Long-lasting phosphorescence of Eu2+ in melilite

UV excitation for several Eu2+-doped melilite crystals produces long-lasting phosphorescence (1–102 s) from Eu2+ ions besides the intrinsic Eu2+ 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 most intense phosphorescence was obtained from the CaSrAl2SiO7 (CSASM) crystal. The intensities of the phosphorescence at the peak wavelength of 520 nm in CSASM were measured as functions of temperature and time. The decay curves in various temperatures fit t−n (n∼0.9). This fact shows that the recombination of the pairs occurs through tunneling. The intensities of the phosphorescence integrated in a time domain increase with an increase of temperature from 10 to 200 K, reach a maximum at 200 K and decrease by non-radiative decay process above 200 K.