Self-activated long persistent luminescence from different trapping centers of calcium germanate

Ca2Ge7O16 phosphor with a self-activated LPL was synthesized. The unique emission of Ca2Ge7O16 related to the creation of the oxygen vacancies was proved. With increasing concentration of Nd3+, the LPL peaks in these phosphors red-shift obviously, which results in the corresponding emitting color changing from purple to blue. The thermoluminescence spectra indicate that there are two different types of traps, which are attributed to oxygen and calcium vacancies, respectively. Both of them not only act as the trapping centers, but also as the exciton energy-level involved in the emission process. Accordingly, the mechanism of the LPL process was discussed briefly.