Fluorescence from CaYAl3O7 (CYAM) melilite crystal doped with Ce3+ excited at 266 or 355 nm has a broad band with a peak at 430 nm. The decay time of the Ce3+ fluorescence is 45 ns below 300 K. Persistent phosphorescence, of which the line shape is the same as that of the Ce3+ fluorescence, has fairly long decay times distributed in the range from 1 to 1000 s. After irradiating CYAM:Ce with the UV light at 300 K, ESR spectra measured at 77 K consist of a single resonance line with a g value of 2.002 and two sets of the sextet-hyperfine lines with a g value of 2.012 due to the hyperfine coupling with Al nuclear spin (I = 5/2). The g values of these ESR lines indicate that an electron is trapped at an oxygen vacancy and a hole is self-trapped around a single Al3+ ion. We have proposed a mechanism responsible for the persistent phosphorescence in CYAM: Ce, taking into account the crystal structure and the ESR results.

Keywords: Persistent phosphorescence; Electron-spin resonance; Photoconductivity; Cerium ions; Melilite crystal