123 巻 (2015) 1444 号 p. 1059-1064
Ce3+-doped garnet materials have attracted a great deal of attention in w-LEDs and scintillators applications because of their various optical properties. In 2011, we reported intense photocurrent by blue light excitation in Y3Al5−xGaxO12 (Yttrium Aluminum Gallium Garnet, YAGG):Ce3+ phosphors with high Ga content. With increasing Ga content in YAGG:Ce, the energy gap between the lowest excited 5d level (5d1) and the conduction band (CB) decreases because the crystal filed splitting of Ce3+ becomes much smaller and the CB energy decreases. Based on the photoconductivity results, we concluded that Y3Al2Ga3O12:Ce3+ luminescence is quenched by thermal ionization. Utilizing the thermally assisted photoionization by blue light excitation, we tried to prepare a blue light chargeable persistent phosphor. In 2013, we found that Cr3+ ions act as suitable electron traps for persistent luminescence at room temperature in YAGG:Ce3+, and successfully developed the blue light chargeable persistent phosphors. In YAGG:Ce3+–Cr3+ persistent phosphors, the charging process (thermal ionization process) and detrapping process were controlled by CB energy engineering.